#### Sample records for porous dielectric thz

1. Dielectric THz waveguides

NASA Astrophysics Data System (ADS)

Dupuis, Alexandre

In this thesis we have explored a wide variety of dielectric waveguides that rely on many different waveguiding mechanisms to guide THz (far-infrared) radiation. We have explored both theoretically and experimentally a large number of waveguide designs with the aim of reducing propagation and bending losses. The different waveguides can be classified into two fundamentally different strategies for reducing the propagation loss: small-core single-mode evanescent-field fibers or large hollow-core multi-mode tubes. Our focus was first set on exploring the small-core evanescent-field fiber strategy for reducing propagation losses. Following initial theoretical work in our group, much effort was spent on the fabrication and measurement of evanescent porous subwavelength diameter plastic fibers, in an attempt to further reduce the propagation losses. The fabrication of such fibers is a challenge and many novel techniques were devised to enable fiber drawing without hole collapse. The first method sealed the holes of an assembly of polymer tubes and lead to fibers of relatively low porosity (˜25% air within the core) due to reduction in hole size during fiber drawing. The second method was a novel sacrificial polymer technique whereby drawing a completely solid fiber prevented any hole collapse and the subsequent dissolution of the sacrificial polymer revealed the holes in the fiber. The third method was a combination of preform casting using glass molds and drawing with pressurized air within the holes. This led to fibers of record porosity (86% air). The measurement of these porous fibers began with a collaboration with a group from the university of Sherbrooke. At the time, the only available detector was a frequency integrating liquid-helium-cooled bolometer (powermeter). A novel directional coupler method for measuring the losses of subwavelength fibers was developed whereby an evanescent coupler is formed by bringing a probe fiber in proximity to the sample fiber

2. Extremely sub-wavelength THz metal-dielectric wire microcavities.

PubMed

Feuillet-Palma, Cheryl; Todorov, Yanko; Steed, Robert; Vasanelli, Angela; Biasiol, Giorgio; Sorba, Lucia; Sirtori, Carlo

2012-12-17

We demonstrate minimal volume wire THz metal-dielectric micro-cavities, in which all but one dimension have been reduced to highly sub-wavelength values. The smallest cavity features an effective volume of 0.4 µm(3), which is ~5.10(-7) times the volume defined by the resonant vacuum wavelength (λ = 94 µm) to the cube. When combined with a doped multi-quantum well structure, such micro-cavities enter the ultra-strong light matter coupling regime, even if the total number of electrons participating to the coupling is only in the order of 10(4), thus much less than in previous studies.

3. Dielectric Study of Alcohols Using Broadband Terahertz Time Domain Spectroscopy (THz-TDS).

NASA Astrophysics Data System (ADS)

Sarkar, Sohini; Saha, Debasis; Banerjee, Sneha; Mukherjee, Arnab; Mandal, Pankaj

2016-06-01

Broadband Terahertz-Time Domain Spectroscopy (THz-TDS) (1-10 THz) has been utilized to study the complex dielectric properties of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and 1-octanol. Previous reports on dielectric study of alcohols were limited to 5 THz. At THz (1 THz = 33.33 wn = 4 meV) frequency range (0.1 to 15 THz), the molecular reorientation and several intermolecular vibrations (local oscillation of dipoles) may coexist and contribute to the overall liquid dynamics. We find that the Debye type relaxations barely contribute beyond 1 THz, rather three harmonic oscillators dominate the entire spectral range. To get insights on the modes responsible for the observed absorption in THz frequency range, we performed all atom molecular dynamics (MD) using OPLS force field and ab initio quantum calculations. Combined experimental and theoretical study reveal that the complex dielectric functions of alcohols have contribution from a) alkyl group oscillation within H-bonded network ( 1 THz), b) intermolecular H-bond stretching ( 5 THz) , and c) librational motions in alcohols. The present work, therefore, complements all previous studies on alcohols at lower frequencies and provides a clear picture on them in a broad spectral range from microwave to 10 THz.

4. Analysis of high voltage dielectric insulation materials of XLPE by THz-TDS system

NASA Astrophysics Data System (ADS)

Shi, Wei; Yan, Zhijin; Yang, Lei; Dai, Yang; Zhang, Like; Bian, Kangkang; Hou, Lei

2015-11-01

In this paper, cross-linked polyethylene (XLPE) was analyzed by THz time domain spectroscopy (TDS) system at room temperature. By recording time domain signal of terahertz radiation field, frequency spectrum can be obtained by Fourier transform. Then the refractive index and dielectric constant in THz band are calculated. This proves that the THz-TDS system has a potential application for detecting the aging characteristic of XLPE.

5. THz transmission characteristics of dielectric-filled parallel-plate waveguides

NASA Astrophysics Data System (ADS)

Mendis, Rajind

2007-04-01

THz transmission characteristics of dielectric-filled (DF) metallic parallel-plate waveguides (PPWGs) are experimentally and theoretically investigated via the propagation of sub-ps THz pulses. It is found that a PPWG having a high-resistivity (>10 kΩ cm) silicon filling can, in fact, exhibit a higher transmission loss compared to one having a polythene filling, despite the significantly lower THz absorption in the bulk silicon. Consequently, it is shown that the key to achieving low-loss transmission in DF-PPWGs is to use a dielectric filling having not only a low absorption, but also a low refractive index. The application of this guided-wave geometry for THz spectroscopy of minute (film) substances is also predicted.

6. THz - ToF Optical Layer Analysis (OLA) to determine optical properties of dielectric materials

NASA Astrophysics Data System (ADS)

Spranger, Holger; Beckmann, Jörg

2017-02-01

Electromagnetic waves with frequencies between 0.1 and 10 THz are described as THz-radiation (T-ray). The ability to penetrate dielectric materials makes T-rays attractive to reveal discontinuities in polymer and ceramic materials. THz-Time Domain Spectroscopy Systems (THz-TDS) are available on the market today which operates with THz-pulses transmitted and received by optically pumped semiconductor antennas. In THz-TDS the travelling time (ToF) and shape of the pulse is changed if it interacts with the dielectric material and its inherent discontinuities. A tomogram of the object under the test can be reconstructed from time of flight diffraction (ToFD) scans if a synthetic focusing aperture (SAFT) algorithm is applied. The knowledge of the base materials shape and optical properties is essential for a proper reconstruction result. To obtain these properties a model is assumed which describes the device under the test as multilayer structure composed of thin layers with different dielectric characteristics. The Optical Layer Analysis (OLA) is able to fulfill these requirements. A short description why the optical properties are crucial for meaningful SAFT reconstruction results will be given first. Afterwards the OLA will be derived and applied on representative samples to discuss and evaluate its benefits and limits.

7. The source of THz radiation based on dielectric waveguide excited by sequence of electron bunches

NASA Astrophysics Data System (ADS)

Altmark, A. M.; Kanareykin, A. D.

2016-07-01

We present a new method for excitation of THz Cherenkov radiation in a dielectric waveguide by relativistic electron bunches. A sequence of bunches generates monochromatic radiation. The frequency of radiation is defined by the distance between the bunches. The studies were carried by using the newly updated BBU-3000 code which permits taking into account a number of additional options: an external quadrupole focusing system, group velocity of the wakefield, and the dielectric material loss factor. In this paper, we present our algorithm for optimizing the number and sequential positions of bunches for generation of narrow band high power THz radiation.

8. Tunable THz radiation source from dielectric loaded waveguide excited by nonrelativistic electron bunch trains

NASA Astrophysics Data System (ADS)

Li, Weiwei; He, Zhigang; Lu, Yalin; Huang, Ruixuan; Liu, Weihao; Jia, Qika; Wang, Lin

2016-10-01

We propose a novel scheme to generate a tunable narrow-band THz radiation. In this scheme, a train of laser pulses with THz repetition rate is used to drive a photocathode direct current (DC) gun, leading to the emission of a train of electron bunches. The electron bunch train is subsequently accelerated by the gun field and applied to selectively excite one of the modes in the dielectric loaded waveguide (DLW) structure, which is located downstream the DC gun. Thanks to the tunability of the repetition rate of laser pulses and the gun voltage, a tunable narrow-band THz radiation source can be obtained. This proposed source has the advantages of compactness, robustness and relatively high power.

9. Efficient extraction of high power THz radiation generated by an ultra-relativistic electron beam in a dielectric loaded waveguide

NASA Astrophysics Data System (ADS)

Antipov, S.; Baryshev, S. V.; Kostin, R.; Baturin, S.; Qiu, J.; Jing, C.; Swinson, C.; Fedurin, M.; Wang, D.

2016-10-01

We have measured an intense THz radiation produced by a sub-picosecond, relativistic electron bunch in a dielectric loaded waveguide. For efficient THz pulse extraction, the dielectric loaded waveguide end was cut at an angle. For an appropriate choice of angle cut, such antenna converts the TM01 mode excited in the waveguide into a free-space fundamental Gauss-Hermite mode propagating at an angle with respect to the electron beam trajectory. Simulations show that more than 95% of energy can be extracted using such a simple approach. More than 40 oscillations of about 170 ps long 0.48 THz signal were explicitly measured with an interferometer and 10 μJ of energy per pulse, as determined with a calorimetric energy meter, were delivered outside the electron beamline to an area suitable for THz experiments.

10. Efficient extraction of high power THz radiation generated by an ultra-relativistic electron beam in a dielectric loaded waveguide

DOE PAGES

Antipov, S.; Baryshev, S. V.; Kostin, R.; ...

2016-10-03

Here, we have measured an intense THz radiation produced by a sub-picosecond, relativistic electron bunch in a dielectric loaded waveguide. For efficient THz pulse extraction, the dielectric loaded waveguide end was cut at an angle. For an appropriate choice of angle cut, such antenna converts the TM01 mode excited in the waveguide into a free-space fundamental Gauss-Hermite mode propagating at an angle with respect to the electron beam trajectory. Simulations show that more than 95% of energy can be extracted using such a simple approach. More than 40 oscillations of about 170 ps long 0.48 THz signal were explicitly measuredmore » with an interferometer and 10 μJ of energy per pulse, as determined with a calorimetric energy meter, were delivered outside the electron beamline to an area suitable for THz experiments.« less

11. Efficient extraction of high power THz radiation generated by an ultra-relativistic electron beam in a dielectric loaded waveguide

SciTech Connect

Antipov, S.; Baryshev, S. V.; Kostin, R.; Baturin, S.; Qiu, J.; Jing, C.; Swinson, C.; Fedurin, M.; Wang, D.

2016-10-03

Here, we have measured an intense THz radiation produced by a sub-picosecond, relativistic electron bunch in a dielectric loaded waveguide. For efficient THz pulse extraction, the dielectric loaded waveguide end was cut at an angle. For an appropriate choice of angle cut, such antenna converts the TM01 mode excited in the waveguide into a free-space fundamental Gauss-Hermite mode propagating at an angle with respect to the electron beam trajectory. Simulations show that more than 95% of energy can be extracted using such a simple approach. More than 40 oscillations of about 170 ps long 0.48 THz signal were explicitly measured with an interferometer and 10 μJ of energy per pulse, as determined with a calorimetric energy meter, were delivered outside the electron beamline to an area suitable for THz experiments.

12. Dielectric response of pure and doped-GaSe crystals studied by an indigenously developed broadband THz-TDS system

NASA Astrophysics Data System (ADS)

Das, Amit C.; Bhattacharya, S.; Mandal, K. C.; Mondal, S.; Jewariya, M.; Ozaki, T.; Bhaktha, S. N. B.; Datta, P. K.

2016-04-01

Publisher's Note: This paper, originally published on 12 July 2016, was replaced with a corrected/revised version on 26 July 2016. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance. We have developed a terahertz time domain spectroscopy system (THz TDS). For THz generation, optical rectification process and for detection, electro-optic sampling processes are used. Identical < 110 > cut ZnTe crystals are used for both generation and detection of THz radiation.This spectroscopy system can be used for the noninvasive and contactless electrical and optical characterizations of various samples. In this work spectroscopic measurements of pure, Chromium and Indium doped GaSe crystals within 0.4 THz to 3 THz range are taken by the developed set-up to study the dielectric response of the samples.

13. Fabrication and THz loss measurements of porous subwavelength fibers using a directional coupler method.

PubMed

Dupuis, Alexandre; Allard, Jean-François; Morris, Denis; Stoeffler, Karen; Dubois, Charles; Skorobogatiy, Maksim

2009-05-11

We report several strategies for the fabrication of porous subwavelength fibers using low density Polyethylene plastic for low-loss terahertz light transmission applications. We also characterize transmission losses of the fabricated fibers in terahertz using a novel non-destructive directional coupler method. Within this method a second fiber is translated along the length of the test fiber to probe the power attenuation of a guided mode. The method is especially suitable for measuring transmission losses through short fiber segments, a situation in which standard cutback method is especially difficult to perform. We demonstrate experimentally that introduction of porosity into a subwavelength rod fiber, further reduces its transmission loss by as much as a factor of 10. The lowest fiber loss measured in this work is 0.01 cm(-1) and it is exhibited by the 40% porous subwavelength fiber of diameter 380 microm. For comparison, the loss of a rod-in-the-air subwavelength fiber of a similar diameter was measured to be approximately 0.1 cm(-1), while the bulk loss of a PE plastic used in the fabrication of such fibers is >or= 1 cm(-1). Finally, we present theoretical studies of the optical properties of individual subwavelength fibers and a directional coupler. From these studies we conclude that coupler setup studied in this paper also acts as a low pass filter with a cutoff frequency around 0.3 THz. Considering that the spectrum of a terahertz source used in this work falls off rapidly below 0.25 THz, the reported loss measurements are, thus, the bolometer averages over the approximately 0.25 THz-0.3 THz region.

14. Cu-Induced Dielectric Breakdown of Porous Low-Dielectric-Constant Film

NASA Astrophysics Data System (ADS)

Cheng, Yi-Lung; Lee, Chih-Yen; Huang, Yao-Liang; Sun, Chung-Ren; Lee, Wen-Hsi; Chen, Giin-Shan; Fang, Jau-Shiung; Phan, Bach Thang

2017-02-01

Dielectric breakdown induced by Cu ion migration in porous low-k dielectric films has been investigated in alternating-polarity bias conditions using a metal-insulator-metal capacitor with Cu top metal electrode. The experimental results indicated that Cu ions migrated into the dielectric film under stress with positive polarity, leading to weaker dielectric strength and shorter time to failure (TTF). In the alternating-polarity test, the measured TTFs increased with decreasing stressing frequency, implying backward migration of Cu ions during reverse-bias stress. Additionally, compared with a direct-current stress condition, the measured TTFs were higher as the frequency was decreased to 10-2 Hz. The electric-field acceleration factor for porous low-k dielectric film breakdown in the alternating-polarity test was also found to increase. This Cu backward migration effect is effective when the stressing time under negative polarity is longer than 0.1 s.

15. Wakefields in THz cylindrical dielectric lined waveguides driven by femtosecond electron bunches

NASA Astrophysics Data System (ADS)

Nie, Yuancun

2015-01-01

This paper reports the wakefield effects driven by a high-intensity relativistic electron bunch in a dielectric lined waveguide (DLW). A state-of-the-art electron bunch is employed to serve as the drive bunch, which has an rms length of 10 μm, i.e. 33 fs, and a charge of 200 pC. Such bunch parameters are comparable to those of DESY's FLASH and SLAC's LCLS and FACET facilities. It is demonstrated that coherent Cherenkov radiation (CCR) at the fundamental mode with frequency above 1 THz and accelerating gradient as high as 2 GV/m can be obtained in a single layer cylindrical diamond-DLW structure, as long as the geometrical parameters of the DLW are properly selected to match the drive bunch. Wakefield-induced energy modulations on the drive bunch itself are studied as well, which can be used to reduce its energy spread or to produce microbunches with much shorter length from it. The simulated results agree well with the theoretical predictions. Such wakefields can be used to accelerate or modulate electron bunches with ultra-high gradients, and produce high power THz radiations directly. These properties have potential applications in the fields of compact colliders and advanced radiation sources.

16. Hybrid semiconductor-dielectric metamaterial modulation for switchable bi-directional THz absorbers

NASA Astrophysics Data System (ADS)

Le, Ly Nguyen; Thang, Nguyen Manh; Thuy, Le Minh; Tung, Nguyen Thanh

2017-01-01

There is an increasing interest for electromagnetic metamaterials that show mutable absorption properties with real-time and dynamic control. In this paper, we investigate a modulation of bi-directional metamaterial absorbers that is thermally switchable at terahertz frequencies. The metamaterial absorber is composed of symmetric hybrid semiconductor-dielectric cut-wire-pair structures, whose electromagnetic responses can be actively manipulated by utilizing an external heat source. As increasing the temperature of metamaterials from 300 to 350 K, we demonstrate that the magnetic resonance can be systematically blue-shifted and overlapped with the electric resonance, which is unaffectedly settled at about 0.8 THz. This superposition provides an effective mechanism to control the absorption intensity from 43% to nearly 95%. Finite integration simulation technique, standard retrieval method, and equivalent circuit model are employed to elaborate our idea.

17. Porous low dielectric constant materials for microelectronics.

PubMed

Baklanov, Mikhail R; Maex, Karen

2006-01-15

Materials with a low dielectric constant are required as interlayer dielectrics for the on-chip interconnection of ultra-large-scale integration devices to provide high speed, low dynamic power dissipation and low cross-talk noise. The selection of chemical compounds with low polarizability and the introduction of porosity result in a reduced dielectric constant. Integration of such materials into microelectronic circuits, however, poses a number of challenges, as the materials must meet strict requirements in terms of properties and reliability. These issues are the subject of the present paper.

18. A computational component analysis of dielectric relaxation and THz spectra of water/AOT reverse micelles with different water loading

NASA Astrophysics Data System (ADS)

Schmollngruber, Michael; Braun, Daniel; Steinhauser, Othmar

2016-12-01

In this computational study, we present molecular dynamics simulations of water/aerosol-OT/isooctane reverse micelles with different water loading. We compare these systems in terms of a detailed analysis of dielectric relaxation spectra and water librations in the THz region. The spectra are decomposed into contributions by molecular species and contributions from individual water solvation shells. Additionally, micellar tumbling motion is shown to have a profound influence on the observed dielectric relaxation spectra, if relaxation by internal reorganization and micellar tumbling occurs within similar time scales. A formalism to directly quantify the effect of micellar tumbling motion on a recorded dielectric spectrum is developed. Since micellar rotational diffusion obeys the laws of hydrodynamics, this method is applicable in an experimental context as well, only knowing the viscosity of the outside medium and the average volume of the reverse micelle.

19. Heat Induced Damage Detection by Terahertz (THz) Radiation

NASA Astrophysics Data System (ADS)

Rahani, Ehsan Kabiri; Kundu, Tribikram; Wu, Ziran; Xin, Hao

2011-06-01

Terahertz (THz) and sub-terahertz imaging and spectroscopy are becoming increasingly popular nondestructive evaluation techniques for damage detection and characterization of materials. THz radiation is being used for inspecting ceramic foam tiles used in TPS (Thermal Protection System), thick polymer composites and polymer tiles that are not good conductors of ultrasonic waves. Capability of THz electromagnetic waves in detecting heat induced damage in porous materials is investigated in this paper. Porous pumice stone blocks are subjected to long time heat exposures to produce heat induced damage in the block. The dielectric properties extracted from THz TDS (Time Domain Spectroscopy) measurements are compared for different levels of heat exposure. Experimental results show noticeable and consistent change in dielectric properties with increasing levels of heat exposure, well before its melting point.

20. Dielectric breakdown in nano-porous thin films

NASA Astrophysics Data System (ADS)

Borja, Juan Pablo

Unknown to most computer users and mobile device enthusiasts, we have finally entered into a critical age of chip manufacturing. January of 2014 marks the official start of the quest by the semiconductor industry to successfully integrate sub 14nm process technology nodes in accordance to the International Technology Roadmap for Semiconductors (ITRS). The manufacturing of nano-scale features represents a major bottleneck of its own. However, a bigger challenge lies in reliably isolating the massive chip interconnect network. The present work is aimed at generating a theoretical and experimental framework to predict dielectric breakdown for thin films used in computer chip components. Here, a set of experimental techniques are presented to assess and study dielectric failure in novel thin films. A theory of dielectric breakdown in thin nano-porous films is proposed to describe combined intrinsic and metal ion catalyzed failure. This theory draws on experimental evidence as well as fundamental concepts from mass and electronic charge transport. The drift of metal species was found to accelerate intrinsic dielectric failure. The solubility of metals species such as Cu was found to range from 7.0x1025 ions/m3 to 1.86x1026 ions/m3 in 7% porous SiCOH films. The diffusion coefficient for Cu species was found to span from 4.2x10-19 m2/s to 1.86x10-21 m2/s. Ramped voltage stress experiments were used to identify intrinsic failure from metal catalyzed failure. Intrinsic breakdown is defined when time to failure against applied field ramp rate results in ∂(ln(TTF))/∂(ln(R)) ≈ -1. Intrinsic failure was studied using Au. Here, ∂(ln(TTF))/∂(ln(R)) ≈ -0.95, which is an experimental best case scenario for intrinsic failure. Au is commonly reluctant to ionize which means that failure occurs in the absence of ionic species. Metal catalyzed failure was investigated using reactive electrodes such as Cu, and Ag. Here, trends for ∂(ln(TTF))/∂(ln(R)) significantly

1. Simultaneously coherent excitation of multi-modes THz radiation from dielectric loaded waveguide by pre-bunched electron beam

NASA Astrophysics Data System (ADS)

Li, Biaobin; Lu, Yalin; He, Zhigang; Li, Weiwei; Jia, Qika; Wang, Lin

2017-02-01

The cylindrical dielectric loaded waveguide (DLW) supports a discrete set of modes, which can be excited by electron beam passing through the structure, and the high-order modes can be the harmonics of the fundamental one by properly choosing the parameters of the DLW. By using a train of electron bunches, repeated at the fundamental frequency of the DLW, as the driving source, coherent and simultaneous excitation of multi-modes can be expected. With this proposed scheme, multi-color narrow-band THz radiation with high pulse power and high frequency can be obtained simultaneously.

2. Functionalization and characterization of porous low-kappa dielectrics

NASA Astrophysics Data System (ADS)

Orozco-Teran, Rosa Amelia

2005-12-01

The incorporation of fluorine into SiO2 has been shown to reduce the dielectric constant of the existing materials by reducing the electrical polarizability. However, the incorporation of fluorine has also been shown to decrease film stability. Therefore, new efforts have been made to find different ways to further decrease the relative dielectric constant value of the existing low-k materials. One way to reduce the dielectric constant is by decreasing its density. This reduces the amount of polarizable materials. A good approach is increasing porosity of the film. Recently, fluorinated silica xerogel films have been identified as potential candidates for applications such as interlayer dielectric materials in CMOS technology. In addition to their low dielectric constants, these films present properties such as low refractive indices, low thermal conductivities, and high surface areas. Another approach to lower kappa is incorporating lighter atoms such as hydrogen or carbon. Silsesquioxane based materials are among them. However, additional integration issues such as damage to these materials caused by plasma etch, plasma ash, and wet etch processes are yet to be overcome. This dissertation reports the effects of triethoxyfluorosilane-based (TEFS) xerogel films when reacted with silylation agents. TEFS films were employed because they form robust silica networks and exhibit low dielectric constants. However, these films readily absorb moisture. Employing silylation reactions enhances film hydrophobicity and permits possible introduction of this film as an interlayer dielectric material. Also, this work describes the effects of SC-CO2 in combination with silylating agents used to functionalize the damaged surface of the ash-damaged MSQ films. Ashed MSQ films exhibit increased water adsorption and dielectric constants due to the carbon depletion and modification of the properties of the low-kappa material caused by interaction with plasma species. CO2 is widely used

3. Dielectric Properties of Porous Si3N4-SiO2-BN Composites

NASA Astrophysics Data System (ADS)

Sun, Yinbao; Zhang, Yumin; Li, Dihong; Han, Jiecai

Porous Si3N4-SiO2-BN composites were prepared by adding starch as both pore former and consolidator. Bruggeman effective-medium model, Maxwell-Garnett model and logarithmic model were used to describe and predict the dielectric constant of porous Si3N4-SiO2-BN ceramics. Relative dielectric constant of porous Si3N4-SiO2-BN composites decreases with the increase of apparent porosity within limits, and these models can forecast the change of the dielectric constant of the porous ceramics quite well. The minimum relative dielectric constant is 2.5 at the apparent porosity of 0.555 at room-temperature. The relationship between dielectric constant and temperature were investigated. It was found dielectric constant varied a lot with the increase of temperature, and Debye relaxation theory was employed to explain the variation of the dielectric constant with temperature increment. But the Debye relaxation theory can not explain the reason of variation of dielectric constant at the temperature range from 300°C to 900°C. To ascertain the cause of changes of dielectric constant at this temperature region, differential scanning calorimentry (DSC) measurement was performed. In this temperature region, phase transition behavior occurs at nearly 300°C in the porous composites. The new phase probably has a tidy large dielectric constant, and the dielectric constant increases sharply.

4. A novel porous silicon-based multilayer dielectric-grating structures for diffraction-based sensing

NASA Astrophysics Data System (ADS)

Mo, Jiaqing; Liu, Yajun; Lv, Changwu; Lv, Xiaoyi; Jia, Zhenhong

2014-11-01

Porous silicon material and device has attracted more attention for use as biochemical optical sensors. In this paper, A novel porous silicon-based multilayer dielectric-grating structures by adding high-reflectivity porous silicon stacks between the substrate and grating was fabricated, and the porous silicon grating height was set to be about 200 nm, the grating period was 4 μm, the air filling factor was 50%. A new better method of preparing this porous silicon-based multilayer dielectric-grating structures have also been employed.

5. Thermal stability of low dielectric constant porous silica films

NASA Astrophysics Data System (ADS)

Esposito, L.; Ottaviani, G.; Carollo, E.; Bacchetta, M.

2005-12-01

Thermal stability of porous-silica-based low dielectric constant, k, material deposited by chemical vapor deposition has been investigated in a wide temperature range. The films as-deposited and after heat treatments up to 600°C have Si1O1.6C1.4H2.3 composition, permittivity k ≈2.8, and porosity h ≈0.25. A skeleton of silicon dioxide and empty pores justifies the permittivity and porosity values. Permeation experiments with deuterated water vapor indicate that pores are interconnected. At 700°C, the film has Si1O1.6C1.4H1.4 composition, k ≈2.4, and h ≈0.21. Bonds with lower polarizability could be responsible for the decrease of k. Above 800°C, carbon segregation and nanoclusters formation occur.

6. Spectral and spatial nondestructive examination of dielectric materials with THz time domain spectroscopy

NASA Astrophysics Data System (ADS)

Beckmann, J.; von Chrzanowski, L. S.; Fratzscher, D.; Ewert, U.

2012-05-01

A time domain spectrometer T-ray 2000® operating in the range of 0.2-2 THz was used for Time of Flight measurements. A series of ethanol water mixtures from 10% to 90% were produced subsequently filled in polystyrene cells and analyzed in the T-ray 2000 TDS system in the reflection mode. The reflectivity of the material liquid interface is strongly influenced by the ethanol concentration in water. The reciprocal reflection coefficient of the material liquid interface was found to be a useful discriminating feature for further Probably of Detection calculations which can be used for the performance evaluation of potential THz bottle scanners. THz pulse echo (PE) measurements were performed in comparison to the established ultra sound PE technique for flaw detection of plastics. Synthetic aperture reconstructions were applied for simulated data to reconstruct the flaw shape. The results were compared with B-scan images of a high density polyethylene (HDPE) test cylinder. Existing restrictions on the quality of the back projected images and limits of the existing model are discussed in detail.

7. Experimental Plans to Explore Dielectric Wakefield Acceleration in the THZ Regime

SciTech Connect

Lemery, F.; Mihalcea, D.; Piot, P.; Behrens, C.; Elsen, E.; Flottmann, K.; Gerth, C.; Kube, G.; Schmidt, B.; Osterhoff, J.; Stoltz, P.

2011-09-07

Dielectric wakefield accelerators have shown great promise toward high-gradient acceleration. We investigate the performances of a possible experiment under consideration at the FLASH facility in DESY to explore wakefield acceleration with an enhanced transformer ratio. The experiment capitalizes on a unique pulse shaping capability recently demonstrated at this facility. In addition, the facility incorporates a superconducting linear accelerator that could generate bunch trains with closely spaced bunches thereby opening the exploration of potential dynamical effects in dielectric wakefield accelerators.

8. Time-dependent dielectric breakdown measurements of porous organosilicate glass using mercury and solid metal probes

SciTech Connect

Pei, Dongfei; Nichols, Michael T.; Shohet, J. Leon; King, Sean W.; Clarke, James S.; Nishi, Yoshio

2014-09-01

Time-dependent dielectric breakdown (TDDB) is one of the major concerns for low-k dielectric materials. During plasma processing, low-k dielectrics are subjected to vacuum ultraviolet photon radiation and charged-particle bombardment. To examine the change of TDDB properties, time-to-breakdown measurements are made to porous SiCOH before and after plasma exposure. Significant discrepancies between mercury and solid-metal probes are observed and have been shown to be attributed to mercury diffusion into the dielectric porosities.

9. Mechanical property changes in porous low-k dielectric thin films during processing

NASA Astrophysics Data System (ADS)

Stan, G.; Gates, R. S.; Kavuri, P.; Torres, J.; Michalak, D.; Ege, C.; Bielefeld, J.; King, S. W.

2014-10-01

The design of future generations of Cu-low-k dielectric interconnects with reduced electronic crosstalk often requires engineering materials with an optimal trade off between their dielectric constant and elastic modulus. This is because the benefits associated with the reduction of the dielectric constant by increasing the porosity of materials, for example, can adversely affect their mechanical integrity during processing. By using load-dependent contact-resonance atomic force microscopy, the changes in the elastic modulus of low-k dielectric materials due to processing were accurately measured. These changes were linked to alterations sustained by the structure of low-k dielectric films during processing. A two-phase model was used for quantitative assessments of the elastic modulus changes undergone by the organosilicate skeleton of the structure of porous and pore-filled dielectrics.

10. Mechanical property changes in porous low-k dielectric thin films during processing

SciTech Connect

Stan, G. Gates, R. S.; Kavuri, P.; Torres, J.; Michalak, D.; Ege, C.; Bielefeld, J.; King, S. W.

2014-10-13

The design of future generations of Cu-low-k dielectric interconnects with reduced electronic crosstalk often requires engineering materials with an optimal trade off between their dielectric constant and elastic modulus. This is because the benefits associated with the reduction of the dielectric constant by increasing the porosity of materials, for example, can adversely affect their mechanical integrity during processing. By using load-dependent contact-resonance atomic force microscopy, the changes in the elastic modulus of low-k dielectric materials due to processing were accurately measured. These changes were linked to alterations sustained by the structure of low-k dielectric films during processing. A two-phase model was used for quantitative assessments of the elastic modulus changes undergone by the organosilicate skeleton of the structure of porous and pore-filled dielectrics.

11. Study of counting characteristics of porous dielectric detectors of radiations

NASA Astrophysics Data System (ADS)

Lorikyan, M. P.

2003-12-01

Multiwire and microstrip porous detectors have been developed and investigated for DC operation. The multiwire porous detector consists of anode wires, an Al cathode and a gap between them filled with porous CsI. The microstrip porous detector consists of an insulating plate covered with metallic strips, micromesh cathode and a gap between them filled with porous CsI. For some time after being manufactured, these detectors' performances are non-stable and they have poor spatial resolution. However, after being kept in vacuum for a certain time, they spontaneously acquire stability and spatial resolution better than 100 μm and have detection efficiencies of 100% and 70% for heavily ionizing α-particles and 5.9 keV X-rays, respectively. The MWPDD performs stably at an intensity of heavily ionizing α-particles of 711 cts/(cm 2 s).

12. Optical properties of multilayered Period-Doubling and Rudin-Shapiro porous silicon dielectric heterostructures

NASA Astrophysics Data System (ADS)

Agarwal, V.; Mora-Ramos, Miguel E.; Alvarado-Tenorio, B.

2009-05-01

To investigate the optical properties in quasi-regular porous-silicon-based dielectric Period-Doubling and Rudin-Shapiro multilayer systems, we study here the reflection of light from these structures. The Period-Doubling and Rudin-Shapiro structures are fabricated in such a way that the optical thickness of each layer is one quarter of 600 and 640 nm respectively. We find that porous silicon Period-Doubling dielectric multilayers could demonstrate the optical properties similar to the classical periodic Febry-Perot interference filters with one or multiple resonant peaks, but with an advantage of having total optical thickness much lesser than the periodic structures. Additionally, light propagation in porous silicon Rudin-Shapiro structures is investigated for the first time, both theoretically and experimentally. The reflectance spectra of the structures exhibit photonic band gaps centered at predetermined wavelengths. In both cases, numerical simulation of light transmission is performed using transfer matrix method.

13. Image x-ray emission converters and microstrip porous dielectric x-ray detector

SciTech Connect

Lorikyan, M. P.

2008-11-01

The effective, fast, and accurate registration of x ray depends on the quality conversion of the X-quanta to photoelectrons. In this respect, of high interest are porous x-ray emission converters (PXECs). They are analogs of porous secondary electron emitters (PSEEs); the only difference is that active porous material should have high absorption properties for the X-quanta energies to be detected. Microstrip porous dielectric detector (MSPDD) is highly effective for x-ray registration without preliminary conversion of the X-quanta. Earlier it was shown that PSEE similar to PXEC has a high emission factor for 1-2 MeV {beta}-particles and 5 MeV {alpha}-particles. It was shown that MSPDDs and PSEEs are very stable.

14. Mechanistic study of plasma damage to porous low-k: Process development and dielectric recovery

NASA Astrophysics Data System (ADS)

Shi, Hualiang

Low-k dielectrics with porosity are being introduced to reduce the RC delay of Cu/low-k interconnect. However, during the O2 plasma ashing process, the porous low-k dielectrics tend to degrade due to methyl depletion, moisture uptake, and densification, increasing the dielectric constant and leakage current. This dissertation presents a study of the mechanisms of plasma damage and dielectric recovery. The kinetics of plasma interaction with low-k dielectrics was investigated both experimentally and theoretically. By using a gap structure, the roles of ion, photon, and radical in producing damage on low-k dielectrics were differentiated. Oxidative plasma induced damage was proportional to the oxygen radical density, enhanced by VUV photon, and increased with substrate temperature. Ion bombardment induced surface densification, blocking radical diffusion. Two analytical models were derived to quantify the plasma damage. Based on the radical diffusion, reaction, and recombination inside porous low-k dielectrics, a plasma altered layer model was derived to interpret the chemical effect in the low ion energy region. It predicted that oxidative plasma induced damage can be reduced by decreasing pore radius, substrate temperature, and oxygen radical density and increasing carbon concentration and surface recombination rate inside low-k dielectrics. The model validity was verified by experiments and Monte-Carlo simulations. This model was also extended to the patterned low-k structure. Based on the ion collision cascade process, a sputtering yield model was introduced to interpret the physical effect in the high ion energy region. The model validity was verified by checking the ion angular and energy dependences of sputtering yield using O2/He/Ar plasma, low-k dielectrics with different k values, and a Faraday cage. Low-k dielectrics and plasma process were optimized to reduce plasma damage, including increasing carbon concentration in low-k dielectrics, switching plasma

15. THz Cherenkov radiation of Josephson vortex

NASA Astrophysics Data System (ADS)

Malishevskii, A. S.; Silin, V. P.; Uryupin, S. A.; Uspenskii, S. G.

2008-01-01

It is shown that Josephson vortices travelling in sandwich embedded in dielectric media radiate electromagnetic waves with THz frequencies. This phenomenon is caused by the Cherenkov effect and takes place if vortex velocity exceeds the speed of light in dielectric.

16. Estimating the extent of surface oxidation by measuring the porosity dependent dielectrics of oxygenated porous silicon [rapid communication

NASA Astrophysics Data System (ADS)

Pan, L. K.; Sun, Chang Q.; Li, C. M.

2005-02-01

Surface oxidation and porosity variation play significant roles in the dielectric performance of porous silicon (PS) yet discriminating the contribution of these events is a challenge. Here we present an analytical solution that covers contributions from the components of silicon oxide surface, silicon backbone and voids using a serial-parallel capacitance structure. Agreement between modeling predictions and measurement has been realized, which turns out an effective method that enables us to estimate the extent of surface oxidation of a specimen by measuring the porosity dependent dielectric response of the chemically passivated PS, and provides guidelines that could be useful for designing dielectric porous structures with surface oxidation.

17. Role of copper in time dependent dielectric breakdown of porous organo-silicate glass low-k materials

NASA Astrophysics Data System (ADS)

Zhao, Larry; Pantouvaki, Marianna; Croes, Kristof; Tőkei, Zsolt; Barbarin, Yohan; Wilson, Christopher J.; Baklanov, Mikhail R.; Beyer, Gerald P.; Claeys, Cor

2011-11-01

The role of copper in time dependent dielectric breakdown (TDDB) of a porous low-k dielectric with TaN/Ta barrier was investigated on a metal-insulator-metal capacitor configuration where Cu ions can drift into the low-k film by applying a positive potential on the top while they are not permitted to enter the low-k dielectric if a negative potential is applied on the top. No difference in TDDB performance was observed between the positive and negative bias conditions, suggesting that Cu cannot penetrate TaN/Ta barrier to play a critical role in the TDDB of porous low-k material.

18. Determination of excitation profile and dielectric function spatial nonuniformity in porous silicon by using WKB approach.

PubMed

He, Wei; Yurkevich, Igor V; Canham, Leigh T; Loni, Armando; Kaplan, Andrey

2014-11-03

We develop an analytical model based on the WKB approach to evaluate the experimental results of the femtosecond pump-probe measurements of the transmittance and reflectance obtained on thin membranes of porous silicon. The model allows us to retrieve a pump-induced nonuniform complex dielectric function change along the membrane depth. We show that the model fitting to the experimental data requires a minimal number of fitting parameters while still complying with the restriction imposed by the Kramers-Kronig relation. The developed model has a broad range of applications for experimental data analysis and practical implementation in the design of devices involving a spatially nonuniform dielectric function, such as in biosensing, wave-guiding, solar energy harvesting, photonics and electro-optical devices.

19. Cellular-automata model of oxygen plasma impact on porous low-K dielectric

NASA Astrophysics Data System (ADS)

Rezvanov, Askar; Matyushkin, Igor V.; Gutshin, Oleg P.; Gornev, Evgeny S.

2016-12-01

Cellular-automata model of oxygen plasma influence on the integral properties of porous low-K dielectric is studied. The present work investigates the imitative simulation of this process. In our model we consider one isolated pore, which is simulated by cylinder with length L=200 nm and radius 1 nm ignoring the curvature factor. The simulation was performed for 2 million automata steps that correspond to 2 seconds in the real process time. Extrapolating the data to the longer time shows that more and more •CH3 groups will be replaced by the •OH groups, and over time almost all methyl groups will leave the pore surface (there is not more than 20% of the initial methyl groups amount on the first low-K dielectric 40nm after 2 seconds simulation).

20. Bandgap measurements of low-k porous organosilicate dielectrics using vacuum ultraviolet irradiation

SciTech Connect

Zheng, H.; Shohet, J. L.; King, S. W.; Ryan, V.; Nishi, Y.

2014-02-10

Vacuum ultraviolet (VUV) photoemission spectroscopy is used to investigate the effect of VUV radiation on porous organosilicate (SiCOH) dielectrics during plasma processing. By comparing photoemission spectroscopic results before and after VUV exposure, VUV irradiation with photon energies less than 9.0 eV was found to be beneficial in depleting accumulated charge in SiCOH films while VUV photons with higher energies did not have this effect. Moreover, VUV irradiation with 8.9 eV photons depletes the most charge. From this result, it can be concluded that 8.9 eV is the bandgap plus the electron affinity energy of SiCOH dielectrics.

1. Water and ion transport in ultra-adsorbing porous magnesium carbonate studied by dielectric spectroscopy

NASA Astrophysics Data System (ADS)

Pochard, Isabelle; Frykstrand, Sara; Ahlström, Olle; Forsgren, Johan; Strømme, Maria

2014-01-01

Porous materials are used in application areas ranging from drug and vaccine delivery, medical implants, molecular sieves and cosmetics to catalysis and humidity control. In the present work, we employed an alternative approach to gain in-depth understanding about water interaction properties in such materials by the use of dielectric spectroscopy and thereby show that it is possible to obtain information that is not accessible from the more commonly employed water interaction analysis techniques. Specifically, the complex dielectric response of Upsalite, a novel, super-hydroscopic, high-surface area, porous magnesium carbonate material was measured in isothermal frequency scans between 10-3 and 106 Hz at controlled relative humidity (RH). We found the dielectric constant of the dry material to be 1.82. The ratio of bound to free water present in Upsalite after adsorption at room temperature was found to be high irrespective of the surrounding humidity with values ranging from ˜67% to ˜90%. We further found that OH- ions are the charge carriers responsible for the electrode polarization observed in the dielectric response and that the amount of these ions that are free to move in the material corresponds to a concentration of the order of 1-10 μmol l-1 independent of RH. Finally, the OH- diffusion coefficient displayed a drastic decrease with decreasing RH, typical of transport in unsaturated conditions. The presented results provide detailed insight about water interactions in the novel water adsorbing material under study and it is foreseen that the employed analysis methods can be used to evaluate other types of moisture adsorbing materials as well as the movement of functional species in the pores of inorganic drug delivery materials and materials tailored for adsorption of harmful charged species.

2. Hierarchical viscosity of aqueous solution of tilapia scale collagen investigated via dielectric spectroscopy between 500 MHz and 2.5 THz

PubMed Central

Kawamata, H.; Kuwaki, S.; Mishina, T.; Ikoma, T.; Tanaka, J.; Nozaki, R.

2017-01-01

Aqueous solutions of biomolecules such as proteins are very important model systems for understanding the functions of biomolecules in actual life processes because interactions between biomolecules and the surrounding water molecules are considered to be important determinants of biomolecules’ functions. Globule proteins have been extensively studied via dielectric spectroscopy; the results indicate three relaxation processes originating from fluctuations in the protein molecule, the bound water and the bulk water. However, the characteristics of aqueous solutions of collagens have rarely been investigated. In this work, based on broadband dielectric measurements between 500 MHz and 2.5 THz, we demonstrate that the high viscosity of a collagen aqueous solution is due to the network structure being constructed of rod-like collagen molecules surrounding free water molecules and that the water molecules are not responsible for the viscosity. We determine that the macroscopic viscosity is related to the mean lifetime of the collagen-collagen interactions supporting the networks and that the local viscosity of the water surrounded by the networks is governed by the viscosity of free water as in the bulk. This hierarchical structure in the dynamics of the aqueous solution of biomolecules has been revealed for the first time. PMID:28345664

3. Porous Polyimide Membranes Prepared by Wet Phase Inversion for Use in Low Dielectric Applications

PubMed Central

Kim, Soohyun; Jang, Keon-Soo; Choi, Hee-Dok; Choi, Seung-Hoon; Kwon, Seong-Ji; Kim, Il-Doo; Lim, Jung Ah; Hong, Jae-Min

2013-01-01

A wet phase inversion process of polyamic acid (PAA) allowed fabrication of a porous membrane of polyimide (PI) with the combination of a low dielectric constant (1.7) and reasonable mechanical properties (Tensile strain: 8.04%, toughness: 3.4 MJ/m3, tensile stress: 39.17 MPa, and young modulus: 1.13 GPa), with further thermal imidization process of PAA. PAA was simply synthesized from purified pyromellitic dianhydride (PMDA) and 4,4-oxydianiline (ODA) in two different reaction solvents such as γ-butyrolactone (GBL) and N-methyl-2-pyrrolidinone (NMP), which produce Mw/PDI of 630,000/1.45 and 280,000/2.0, respectively. The porous PAA membrane was fabricated by the wet phase inversion process based on a solvent/non-solvent system via tailored composition between GBL and NMP. The porosity of PI, indicative of a low electric constant, decreased with increasing concentration of GBL, which was caused by sponge-like formation. However, due to interplay between the low electric constant (structural formation) and the mechanical properties, GBL was employed for further exploration, using toluene and acetone vs. DI-water as a coagulation media. Non-solvents influenced determination of the PAA membrane size and porosity. With this approach, insight into the interplay between dielectric properties and mechanical properties will inform a wide range of potential low-k material applications. PMID:23615465

4. Porous polyimide membranes prepared by wet phase inversion for use in low dielectric applications.

PubMed

Kim, Soohyun; Jang, Keon-Soo; Choi, Hee-Dok; Choi, Seung-Hoon; Kwon, Seong-Ji; Kim, Il-Doo; Lim, Jung Ah; Hong, Jae-Min

2013-04-24

A wet phase inversion process of polyamic acid (PAA) allowed fabrication of a porous membrane of polyimide (PI) with the combination of a low dielectric constant (1.7) and reasonable mechanical properties (Tensile strain: 8.04%, toughness: 3.4 MJ/m3, tensile stress: 39.17 MPa, and young modulus: 1.13 GPa), with further thermal imidization process of PAA. PAA was simply synthesized from purified pyromellitic dianhydride (PMDA) and 4,4-oxydianiline (ODA) in two different reaction solvents such as γ-butyrolactone (GBL) and N-methyl-2-pyrrolidinone (NMP), which produce Mw/PDI of 630,000/1.45 and 280,000/2.0, respectively. The porous PAA membrane was fabricated by the wet phase inversion process based on a solvent/non-solvent system via tailored composition between GBL and NMP. The porosity of PI, indicative of a low electric constant, decreased with increasing concentration of GBL, which was caused by sponge-like formation. However, due to interplay between the low electric constant (structural formation) and the mechanical properties, GBL was employed for further exploration, using toluene and acetone vs. DI-water as a coagulation media. Non-solvents influenced determination of the PAA membrane size and porosity. With this approach, insight into the interplay between dielectric properties and mechanical properties will inform a wide range of potential low-k material applications.

5. Rôle of dielectric effects in the red-green switching of porous silicon luminescence

NASA Astrophysics Data System (ADS)

Chazalviel, J.-N.; Ozanam, F.; Dubin, V. M.

1994-09-01

Trapping of a carrier at an ionized impurity in porous silicon may be significantly hindered when the material is embedded in a high-dielectric-constant medium such as an aqueous electrolyte. This effect is estimated for a geometry of cylindrical silicon wires, and by modeling the two media with wavevector-independent dielectric constants. The self-image potential of the electron is taken into account, and the frequency dependence of the outer dielectric constant is treated in a simple manner. The results demonstrate that the impurity states are not accessible in the presence of the electrolyte, just due to the dielectric relaxation of the embedding medium. This result may apply to different kinds of localized electronic states, including those responsible for the red luminescence in dry porous silicon. This provides a plausible explanation for the red to green switching of the luminescence when the porous silicon is wet and suggests that using embedding media of intermediate dielectric constants should allow one to observe a progressive transition between red and green luminescence. Observation of porous silicon luminescence in solvents of various dielectric constants provides a preliminary test of this prediction. Le piégeage d'un porteur par une impureté ionisée dans le silicium poreux peut devenir inefficace lorsque le matériau est plongé dans un milieu de grande constante diélectrique tel qu'un électrolyte aqueux. Cet effet est estimé pour une géométrie de filaments cylindriques de silicium, les deux milieux étant modélisés par des constantes diélectriques indépendantes du vecteur d'onde. Le potentiel image de l'électron est pris en considération, et la dépendance en fréquence de la constante diélectrique du milieu extérieur est traitée de manière simple. Les résultats démontrent que les états liés sur l'impureté ne sont pas accessibles en présence de l'électrolyte, simplement en raison de la relaxation diélectrique de ce milieu

6. Effect of vacuum ultraviolet and ultraviolet Irradiation on capacitance-voltage characteristics of low-k-porous organosilicate dielectrics

SciTech Connect

Sinha, H.; Lauer, J. L.; Nichols, M. T.; Shohet, J. L.; Antonelli, G. A.; Nishi, Y.

2010-02-01

High frequency capacitance-voltage (C-V) measurements are used to determine the effects of vacuum ultraviolet (VUV) and ultraviolet (UV) irradiation on defect states in porous low-k organosilicate (SiCOH) dielectrics. The characteristics show that VUV photons depopulate trapped electrons from defect states within the dielectric creating trapped positive charge. This is evidenced by a negative shift in the flat-band voltage of the C-V characteristic. UV irradiation reverses this effect by repopulating the defect states with electrons photoinjected from the silicon substrate. Thus, UV reduces the number of trapped positive charges in the dielectric and can effectively repair processing-induced damage.

7. Dielectric Response at THz Frequencies of Mg Water Complexes Interacting with O3 Calculated by Density Functional Theory

DTIC Science & Technology

2012-10-24

vibrational modes in the absorption spectra of various materials. A series of studies have focused on the general concept of constructing dielectric response...has a total of 3N-6 normal mode vibrations . The Schrodinger equation for the harmonic oscillations of these normal modes has known solutions. The...and m is the effective mass contributed by those atoms vibrating in the normal mode . A molecule in stable equilibrium is characterized by all

8. Spin Coating Film Transfer and Hot-Pressing System for Uniform Dielectric Formation and Its Application to Porous Low-k Film Formation

NASA Astrophysics Data System (ADS)

Kawagoe, Masafumi; Adachi, Hideki; Yanagida, Takaaki; Komura, Tomoyuki; Saito, Hidenori; Sato, Norio; Kudou, Kazuhisa; Machida, Katsuyuki

2008-01-01

In this paper, we describe a transfer system that enables to form uniform dielectrics using spin coating film transfer and hot-pressing (STP) technology, and the applicability of a porous low-k material. The STP technology transfers a dielectric from a base film to a wafer by hot pressing in vacuum. We propose a processing unit that enables the handling of both the wafer and the base film. In the transfer unit, we also propose a scheme for transferring a dielectric to wafer uniformly. In the experiments, an organic porous low-k material, porous nanoporous polybenzoxazole dielectric (OxD) is used. The results on the film characteristics show no difference from those obtained by conventional spin coating. STP also enables planarization and sealing for patterned wafers with the porous OxD. It is confirmed that the STP process using porous OxD will be a candidate integration process.

9. Devices and materials for THz spectroscopy: GHz CMOS circuits, periodic hole-arrays and high-frequency dielectric materials

NASA Astrophysics Data System (ADS)

Arenas, Daniel J.

This dissertation is composed of three main projects, linked together by the THz region of the electromagnetic spectrum. In the first project, we detected the radiation from a silicon CMOS circuit, using a fourier transform interferometer. At the time of measurement, this 410 GHz circuit had the highest operating frequency for silicon integrated technology. The measured radiated power from the 410 GHz circuits was in the order of 0.01 muW. This circuit had radiated intensities comparable to those of commercially available black-body sources in the 400 GHz region. The high power and high emission per source area suggested possible spectroscopy applications. We also studied the optical properties of periodic hole-arrays with resonant frequencies in the THz region. Although the transmittance spectra of these structures have been extensively studied, here we present reflectance measurements that allow the analysis of the extinction/absorption spectra. The results were compared to predictions from the trapped-mode theory on the ohmic losses of these systems. Our results did not support the prediction of a suppression of the R + T spectra at the resonant frequency. Also, we studied the time-dependence of femtosecond pulses reflected from periodic hole arrays with resonant frequencies in the NIR region. Our results show that if the trapped modes theory is correct, then the lifetime of these modes are below 100 fs. Finally, in the third project, we studied the Raman active modes of various bismuth pyrochlores Bi3/2ZnNb3/2O7 (BZN), Bi3/2ZnTa3/2O7 (BZT), Bi3/2MgNb 3/2O7 (BMN) and Bi3/2MgTa3/2O 7 (BMT), which have earned recent attention for high-frequency applications. The spectra of the four compositions are very similar, suggesting no major structural differences among these materials. The spectra were compared to those of other pyrochlores and specific discussions are offered for the assignment of each mode. Although there are clear differences between the spectra of

10. Integration of porous low-k dielectrics using post porosity pore protection

NASA Astrophysics Data System (ADS)

Zhang, Liping; de Marneffe, Jean-François; Verdonck, Patrick; Heylen, Nancy; Wen, Liang Gong; Wilson, Chris; Tokei, Zsolt; Boemmels, Juergen; De Gendt, Stefan; Baklanov, Mikhail R.

2016-12-01

Post porosity pore protection is studied as a means for low damage integration of porous low-k dielectrics. Homogeneous low-k densification is achieved using poly(methyl methacrylate) (PMMA) as a sacrificial filler. The improvement in plasma-induced damage is investigated on a plasma-enhanced chemical vapor deposition 2.0 porous organo-silicate glass, including damage from radicals and vacuum ultraviolet photons. Open pores are sealed upon polymer protection; therefore the penetration of metal species during deposition of a metal diffusion barrier is avoided. Various solutions for post metallization polymer removal are investigated, such as hydrogen remote plasma and an ultraviolet cure. The PMMA removal process is studied in order to avoid Cu wire degradation. Finally, low-k damage and barrier continuity are investigated on patterned wafers with functional circuits. By means of transmission electron microscopy inspection and electrical measurement, effective integrated k-values are extracted, giving a value k eff ~ 2.5-2.6 for the post metallization polymer removal option.

11. Porous AlN with a Low Dielectric Constant Synthesized Based on the Physical Vapor Transport Principle

NASA Astrophysics Data System (ADS)

Wang, Hua-Jie; Liu, Xue-Chao; Kong, Hai-Kuan; Xin, Jun; Gao, Pan; Shi, Er-Wei

2016-07-01

Porous AlN with low dielectric constant has been synthesized by the sacrificial template method based on the physical vapor transport principle. It is quite different from the traditional method that mixes the matrix with a pore-forming agent and utilizes liquid-phase sintering. The method consists of two parts. Firstly, AlN powder is placed in a graphite crucible. C/AlN composite can be formed by mixing decomposed AlN vapor and volatile carbon originated from a crucible at high temperature. Secondly, pores are formed after removing carbon from the C/AlN composite by an annealing process. The structure, morphology, porosity and properties of porous AlN are characterized. It is shown the obtained porous AlN has a thermal conductivity of 37.3 W/(m K) and a reduced dielectric constant of 5.5-6.1 (at 1 MHz). The porosity measured by a mercury porosimeter is 24.09%. It has been experimentally proved that porous AlN with a sufficiently porous structure and properties can be synthesized based on the vapor-phase principle.

12. Industrial applications of THz systems

NASA Astrophysics Data System (ADS)

Wietzke, S.; Jansen, C.; Jördens, C.; Krumbholz, N.; Vieweg, N.; Scheller, M.; Shakfa, M. K.; Romeike, D.; Hochrein, T.; Mikulics, M.; Koch, M.

2009-07-01

Terahertz time-domain spectroscopy (THz TDS) holds high potential as a non-destructive, non-contact testing tool. We have identified a plethora of emerging industrial applications such as quality control of industrial processes and products in the plastics industry. Polymers are transparent to THz waves while additives show a significantly higher permittivity. This dielectric contrast allows for detecting the additive concentration and the degree of dispersion. We present a first inline configuration of a THz TDS spectrometer for monitoring polymeric compounding processes. To evaluate plastic components, non-destructive testing is strongly recommended. For instance, THz imaging is capable of inspecting plastic weld joints or revealing the orientation of fiber reinforcements. Water strongly absorbs THz radiation. However, this sensitivity to water can be employed in order to investigate the moisture absorption in plastics and the water content in plants. Furthermore, applications in food technology are discussed. Moreover, security scanning applications are addressed in terms of identifying liquid explosives. We present the vision and first components of a handheld security scanner. In addition, a new approach for parameter extraction of THz TDS data is presented. All in all, we give an overview how industry can benefit from THz TDS completing the tool box of non-destructive evaluation.

13. Advances in Determining Soil Matric Potential Using an Engineered Porous Ceramic and Dielectric Permittivity

NASA Astrophysics Data System (ADS)

Cobos, D. R.; Campbell, C. S.; Campbell, G. S.

2007-12-01

Soil water potential is a key parameter for determining water availability for plant growth, water flow, and soil stability. Although an in situ measurement of matric potential has been the focus of considerable research over the years, existing solutions still have many draw backs such as high maintenance, limited longevity, individual calibration requirements, high cost, and small measurement range. The objective of this research was to develop a sensor that could be used in the field to accurately measure soil matric potential without the limitations noted above. The sensor, which consisted of a dielectric sensor sandwiched between porous ceramic, was tested over a range soil types, electrical conductivties, and temperatures to calibrate and characterize its output. Data show consistent calibration curves between sensor output and actual soil matric potential over a variety of soil textures and electrical conductivities. Although temperature showed an effect on sensor output, it was low compared to overall sensor output. Likewise, salt effects were not visible in saturated matrices up to 10 dS/m. Data suggest the sensor will be an effective and robust tool to determine in situ matric potential.

14. Electro-optical effects in porous PET films filled with liquid crystal: new possibilities for fiber optics and THZ applications.

PubMed

Chopik, A; Pasechnik, S; Semerenko, D; Shmeliova, D; Dubtsov, A; Srivastava, A K; Chigrinov, V

2014-03-15

The results of investigation of electro-optical properties of porous polyethylene terephthalate films filled with a nematic liquid crystal (5 CB) are presented. It is established that the optical response of the samples on the applied voltage drastically depends on the frequency range. At low frequencies of applied electrical field (ffc) electric field induces an overall change in the light intensity, which is typical for an electro-optical response of a liquid crystal (LC) layer in a conventional "sandwich"-like cell. The dependences of critical frequency fc, threshold voltages, and characteristic times on a pore diameter d were established. The peculiarities of electro-optical effects can be explained in the framework of the approach which connects the variations of light intensity with the corresponding changes of the effective refractive index n(eff) of a composite LC media. The unusual behavior of the electro-optical response at low frequencies is assigned to the orienting action of the specific shear flow typical for electrokinetic phenomena in polar liquids.

15. Impact of reductive N2/H2 plasma on porous low-dielectric constant SiCOH thin films

NASA Astrophysics Data System (ADS)

Cui, Hao; Carter, Richard J.; Moore, Darren L.; Peng, Hua-Gen; Gidley, David W.; Burke, Peter A.

2005-06-01

Porous low-dielectric constant (low-κ) SiCOH thin films deposited using a plasma-enhanced chemical-vapor deposition have been comprehensively characterized before and after exposure to a reactive-ion-etch-type plasma of N2 and H2 chemistry. The low-κ film studied in this work is a carbon-doped silicon oxide film with a dielectric constant (κ) of 2.5. Studies show that a top dense layer is formed as a result of significant surface film densification after exposure to N2/H2 plasma while the underlying bulk layer remains largely unchanged. The top dense layer is found to seal the porous bulk SiCOH film. SiCOH films experienced significant thickness reduction, κ increase, and leakage current degradation after plasma exposure, accompanied by density increase, pore collapse, carbon depletion, and moisture content increase in the top dense layer. Both film densification and removal processes during N2/H2 plasma treatment were found to play important roles in the thickness reduction and κ increase of this porous low-κ SiCOH film. A model based upon mutually limiting film densification and removal processes is proposed for the continuous thickness reduction during plasma exposure. A combination of surface film densification, thickness ratio increase of top dense layer to bulk layer, and moisture content increase results in the increase in κ value of this SiCOH film.

16. Integration Process Development for Improved Compatibility with Organic Non-Porous Ultralow-k Dielectric Fluorocarbon on Advanced Cu Interconnects

NASA Astrophysics Data System (ADS)

Gu, Xun; Tomita, Yugo; Nemoto, Takenao; Miyatani, Kotaro; Saito, Akane; Kobayashi, Yasuo; Teramoto, Akinobu; Kuroda, Rihito; Kuroki, Shin-Ichiro; Kawase, Kazumasa; Nozawa, Toshihisa; Matsuoka, Takaaki; Sugawa, Shigetoshi; Ohmi, Tadahiro

2012-05-01

Integration of an organic non-porous ultralow-k dielectric, fluorocarbon (k= 2.2), into advanced Cu interconnects was demonstrated. The challenges of process-induced damage, such as delamination and variances of both the structure and electrical properties of the fluorocarbon during fabrication, were investigated on Cu/fluorocarbon damascene interconnects. A titanium-based barrier layer, instead of a tantalum-based barrier layer, was used to avoid delamination between Cu and fluorocarbon in Cu/fluorocarbon interconnects. A moisture-hermetic dielectric protective layer was also effective to avoid damage induced by wet chemical cleaning. On the other hand, a post-etching nitrogen plasma treatment to form a stable protective layer on the surface of the fluorocarbon was proposed for the practical minimization of damage introduction to fluorocarbon in the following damascene process, such as post-etching cleaning.

17. Vacuum ultra-violet damage and damage mitigation for plasma processing of highly porous organosilicate glass dielectrics

SciTech Connect

Marneffe, J.-F. de Lukaszewicz, M.; Porter, S. B.; Vajda, F.; Rutigliani, V.; Verdonck, P.; Baklanov, M. R.; Zhang, L.; Heyne, M.; El Otell, Z.; Krishtab, M.; Goodyear, A.; Cooke, M.

2015-10-07

Porous organosilicate glass thin films, with k-value 2.0, were exposed to 147 nm vacuum ultra-violet (VUV) photons emitted in a Xenon capacitive coupled plasma discharge. Strong methyl bond depletion was observed, concomitant with a significant increase of the bulk dielectric constant. This indicates that, besides reactive radical diffusion, photons emitted during plasma processing do impede dielectric properties and therefore need to be tackled appropriately during patterning and integration. The detrimental effect of VUV irradiation can be partly suppressed by stuffing the low-k porous matrix with proper sacrificial polymers showing high VUV absorption together with good thermal and VUV stability. In addition, the choice of an appropriate hard-mask, showing high VUV absorption, can minimize VUV damage. Particular processing conditions allow to minimize the fluence of photons to the substrate and lead to negligible VUV damage. For patterned structures, in order to reduce VUV damage in the bulk and on feature sidewalls, the combination of both pore stuffing/material densification and absorbing hard-mask is recommended, and/or the use of low VUV-emitting plasma discharge.

18. Mechanical reliability of porous low-k dielectrics for advanced interconnect: Study of the instability mechanisms in porous low-k dielectrics and their mediation through inert plasma induced re-polymerization of the backbone structure

NASA Astrophysics Data System (ADS)

Sa, Yoonki

Continuous scaling down of critical dimensions in interconnect structures requires the use of ultralow dielectric constant (k) films as interlayer dielectrics to reduce resistance-capacitance delays. Porous carbon-doped silicon oxide (p-SiCOH) dielectrics have been the leading approach to produce these ultralow-k materials. However, embedding of porosity into dielectric layer necessarily decreases the mechanical reliability and increases its susceptibility to adsorption of potentially deleterious chemical species during device fabrication process. Among those, exposure of porous-SiCOH low-k (PLK) dielectrics to oxidizing plasma environment causes the increase in dielectric constant and their vulnerability to mechanical instability of PLKs due to the loss of methyl species and increase in moisture uptake. These changes in PLK properties and physical stability have been persisting challenges for next-generation interconnects because they are the sources of failure in interconnect integration as well as functional and physical failures appearing later in IC device manufacturing. It is therefore essential to study the fundamentals of the interactions on p-SiCOH matrix induced by plasma exposure and find an effective and easy-to-implement way to reverse such changes by repairing damage in PLK structure. From these perspectives, the present dissertation proposes 1) a fundamental understanding of structural transformation occurring during oxidative plasma exposure in PLK matrix structure and 2) its restoration by using silylating treatment, soft x-ray and inert Ar-plasma radiation, respectively. Equally important, 3) as an alternative way of increasing the thermo-mechanical reliability, PLK dielectric film with an intrinsically robust structure by controlling pore morphology is fabricated and investigated. Based on the investigations, stability of PLK films studied by time-dependent ball indentation tester under the elevated temperature, variation in film thickness and

19. Thin film deposition at atmospheric pressure using dielectric barrier discharges: Advances on three-dimensional porous substrates and functional coatings

NASA Astrophysics Data System (ADS)

Fanelli, Fiorenza; Bosso, Piera; Mastrangelo, Anna Maria; Fracassi, Francesco

2016-07-01

Surface processing of materials by atmospheric pressure dielectric barrier discharges (DBDs) has experienced significant growth in recent years. Considerable research efforts have been directed for instance to develop a large variety of processes which exploit different DBD electrode geometries for the direct and remote deposition of thin films from precursors in gas, vapor and aerosol form. This article briefly reviews our recent progress in thin film deposition by DBDs with particular focus on process optimization. The following examples are provided: (i) the plasma-enhanced chemical vapor deposition of thin films on an open-cell foam accomplished by igniting the DBD throughout the entire three-dimensional (3D) porous structure of the substrate, (ii) the preparation of hybrid organic/inorganic nanocomposite coatings using an aerosol-assisted process, (iii) the DBD jet deposition of coatings containing carboxylic acid groups and the improvement of their chemical and morphological stability upon immersion in water.

20. Ultra-broadband THz time-domain spectroscopy of common polymers using THz air photonics.

PubMed

D'Angelo, Francesco; Mics, Zoltán; Bonn, Mischa; Turchinovich, Dmitry

2014-05-19

Terahertz-range dielectric properties of the common polymers low-density polyethylene (LDPE), cyclic olefin/ethylene copolymer (TOPAS®), polyamide-6 (PA6), and polytetrafluoroethylene (PTFE or Teflon®) are characterized in the ultra-broadband frequency window 2-15 THz, using a THz time-domain spectrometer employing air-photonics for the generation and detection of single-cycle sub-50 fs THz transients. The time domain measurements provide direct access to both the absorption and refractive index spectra. The polymers LDPE and TOPAS® demonstrate negligible absorption and spectrally-flat refractive index across the entire spectroscopy window, revealing the high potential of these polymers for applications in THz photonics such as ultra-broadband polymer-based dielectric mirrors, waveguides, and fibers. Resonant high-frequency polar vibrational modes are observed and assigned in polymers PA6 and PTFE, and their dielectric functions in the complete frequency window 2-15 THz are theoretically reproduced. Our results demonstrate the potential of ultra-broadband air-photonics-based THz time domain spectroscopy as a valuable analytic tool for materials science.

1. Peculiarities of the dielectric response of the silver-modified-zeolite porous microstructure

NASA Astrophysics Data System (ADS)

Bunyatova, U.; Ozturk Koc, S.; Orbukh, V. I.; Eyvazova, G. M.; Agamaliev, Z. A.; Lebedeva, N. N.; Koçum, İ. C.; Salamov, B. G.; Ozer, M.

2016-10-01

The aim of this study was to characterize electrical conductivity and dielectrical properties of the silver-exchanged zeolite - natural clinoptilolite from Western part of Turkey and Azerbaijan in the range of frequencies from 200 Hz to 1 MHz and at room temperature. For a better understanding the effect of concentration and content of silver in the nanoporous zeolite volume on the conductivity, a study of the dielectric properties of an un-modified and silver-modified zeolite plates with different amounts of Ag ions and Ag nanoparticles is performed. Un-modified and three different types of the silver ion-exchanged modified clinoptilolite plates were prepared. It was found, that with increasing silver concentration, resistance of zeolite plate monotonically decreases at the same time a capacitance is increases. It is suggested an explanation of the observed frequency dependence of the capacitance and resistance of zeolite plates on the silver concentrations may be explain on the basis of an electrode-dielectric interface gap model. At the same time, the observed phenomenon can be explained by considering the fact that with increasing content of silver the conductivity increases. These results show that Ag nanoparticles play significant role for performance improvement in plasma electronic devices with zeolite cathode.

2. Terahertz Artificial Dielectric Lens

NASA Astrophysics Data System (ADS)

Mendis, Rajind; Nagai, Masaya; Wang, Yiqiu; Karl, Nicholas; Mittleman, Daniel M.

2016-03-01

We have designed, fabricated, and experimentally characterized a lens for the THz regime based on artificial dielectrics. These are man-made media that mimic properties of naturally occurring dielectric media, or even manifest properties that cannot generally occur in nature. For example, the well-known dielectric property, the refractive index, which usually has a value greater than unity, can have a value less than unity in an artificial dielectric. For our lens, the artificial-dielectric medium is made up of a parallel stack of 100 μm thick metal plates that form an array of parallel-plate waveguides. The convergent lens has a plano-concave geometry, in contrast to conventional dielectric lenses. Our results demonstrate that this lens is capable of focusing a 2 cm diameter beam to a spot size of 4 mm, at the design frequency of 0.17 THz. The results further demonstrate that the overall power transmission of the lens can be better than certain conventional dielectric lenses commonly used in the THz regime. Intriguingly, we also observe that under certain conditions, the lens boundary demarcated by the discontinuous plate edges actually resembles a smooth continuous surface. These results highlight the importance of this artificial-dielectric technology for the development of future THz-wave devices.

3. CF3Br plasma cryo etching of low-k porous dielectric

NASA Astrophysics Data System (ADS)

Clemente, I.; Koehler, N.; Miakonkikh, A.; Zimmermann, S.; Schulz, S. E.; Rudenko, K.

2016-08-01

Process of plasma etching of CVD low-k dielectric was studied. We used CF3Br low pressure ICP plasma for etching at cryo temperatures (-20°C — -100°C), pressures (5-20 mTorr) and RF bias with effective DC voltage 80-140 V. Refractive index of film and its thickness were measured by spectral ellipsometry. Ellipsometric porosimetry was employed to compare pore size distribution before and after etching of films. Measurements show increasing of etch rate increase with decreasing sample temperature.

4. Effects of porosity on dielectric and piezoelectric properties of porous lead zirconate titanate ceramics

SciTech Connect

Yang Ankun; Wang Changan; Guo Rui; Huang Yong

2011-04-11

We report porous lead zirconate titanate ceramics fabricated by tert-butyl alcohol-based gel-casting process which show a very high thickness electromechanical coupling coefficient (0.77), high hydrostatic figure of merit (9594x10{sup -15} m{sup 2}/N), and low acoustic impedance (3.7 Mrayls). We show that the porosity effectively affects the performance of the samples in two ways: (1) a higher porosity simplifies the resonance behavior, leading to more efficient energy transduction; (2) its replacement of active ceramic phase leads to low relative permittivity, high hydrostatic figure of merit, and low acoustic impedance. It was confirmed the properties could be tailored by controlling the porosity.

5. Mitigation of plasma-induced damage in porous low-k dielectrics by cryogenic precursor condensation

NASA Astrophysics Data System (ADS)

Zhang, Liping; de Marneffe, Jean-François; Leroy, Floriane; Lefaucheux, Philippe; Tillocher, Thomas; Dussart, Remi; Maekawa, Kaoru; Yatsuda, Koichi; Dussarrat, Christian; Goodyear, Andy; Cooke, Mike; De Gendt, Stefan; Baklanov, Mikhail R.

2016-05-01

The present work describes the plasma etch properties of porous organo-silicate materials at cryogenic temperature. The mechanism of plasma damage is studied by means of in situ ellipsometry and post-etch material evaluation. Using conventional volatile reactants such as SF6, it is found that low plasma damage can be achieved below  -120 °C through two main channels: pore sidewall passivation by molecular SF6 and partial condensation of non-volatile etch by-products. The protection can be enhanced by means of gas phase precursors with low saturated vapor pressure. Using C4F8, complete pore filling is achieved at  -110 °C and negligible plasma-induced damage is demonstrated on both blanket and patterned low-k films. The characteristics of the precursor condensation process are described and discussed in detail, establishing an optimal process window. It is shown that the condensation temperature can be raised by using precursors with even lower vapor pressure. The reported in situ densification through precursor condensation could enable damage-free plasma processing of mesoporous media.

6. Electromagnetic THz Radiation Modeling by DPSM

NASA Astrophysics Data System (ADS)

Rahani, Ehsan Kabiri; Kundu, Tribikram

2012-03-01

THz or T-ray imaging and spectroscopy are becoming increasingly popular nondestructive evaluation techniques for damage detection and characterization of materials. In order to understand the interaction between the T-ray electromagnetic waves and dielectric media a reliable model of electromagnetic wave propagation through dielectric materials must be developed. A recently developed semi-analytical method called the distributed point source method (DPSM) is extended to model electromagnetic wave propagation in THz range. Since T-ray signals generated by emitters or sources are close to Gaussian beams, the DPSM modeling is carried out for Gaussian beams generated by finite sized emitters. The DPSM generated results are compared with the analytical and experimental results. T-ray propagation in layered structures in absence of any anomaly and the interaction between the Gaussian beam and the spherical scatterer are also investigated.

7. Improving interpretation of geoelectrical signatures arising from biomineralization process in porous media: Low-frequency dielectric spectroscopy measurements on Desulfovibrio vulgaris cell suspensions

NASA Astrophysics Data System (ADS)

Zhang, C.; Prodan, C.; Slater, L. D.; Bot, C.; Ntarlagiannis, D.

2009-12-01

Previous geophysical studies have demonstrated the sensitivity of complex conductivity measurements to microbial growth, biofilm formation, and microbial-mineral alternations, indicating that complex conductivity has the potential to serve as non-invasive tool for bioremediation monitoring. However, the inherent dielectric properties of microbes and how they might directly contribute to the geophysical responses observed during microbial-mineral transformations are not well understood. As a first step towards improving the understanding of electrical signals from microbial-mineral transformations in porous media, we studied the low frequency dielectric properties of sulfate-reducing bacteria (Desulfovibrio vulgaris) cell suspensions, a common soil borne microorganism involved in remediation of toxic metals in solution. We utilized a two-electrode dielectric spectroscopy measurement, common in biophysics applications,to acquire high quality dielectric dispersion curves of Desulfovibrio vulgaris cell suspensions over the frequency range 0.1 Hz to 1M Hz. Desulfovibrio vulgaris cell suspensions were placed between two parallel steel electrodes that are enclosed in a cylindrical glass tube, and the complex impedance of sample was measured relative to a known resistor. The measured impedance includes an electrode polarization impedance arising at the interface between electrodes and ionic solutions at low frequencies. This electrode impedance has traditionally precluded the reliable interpretation of two electrode techniques at low frequencies (< 1000 Hz). In order to obtain the true dielectric dispersion curve of sample, we adopt a simple and robust strategy to measure, analyze and remove the polarization impedance. The feasibility of this polarization removal technique was tested on water saturated glass beads. We show that the broadband dielectric response of Desulfovibrio vulgaris can be reliably determined with this approach. The measurements are modeled based on a

8. In-situ surface and interface study of atomic oxygen modified carbon containing porous low-κ dielectric films for barrier layer applications

NASA Astrophysics Data System (ADS)

Bogan, J.; Lundy, R.; P. McCoy, A.; O'Connor, R.; Byrne, C.; Walsh, L.; Casey, P.; Hughes, G.

2016-09-01

The surface treatment of ultralow-κ dielectric layers by exposure to atomic oxygen is presented as a potential mechanism to modify the chemical composition of the dielectric surface to facilitate copper diffusion barrier layer formation. High carbon content, low-κ dielectric films of varying porosity were exposed to atomic oxygen treatments at room temperature, and x-ray photoelectron spectroscopy studies reveal both the depletion of carbon and the incorporation of oxygen at the surface. Subsequent dynamic water contact angle measurements show that the chemically modified surfaces become more hydrophilic after treatment, suggesting that the substrates have become more "SiO2-like" at the near surface region. This treatment is shown to be thermally stable up to 400 °C. High resolution electron energy loss spectroscopy elemental profiles confirm the localised removal of carbon from the surface region. Manganese (≈1 nm) was subsequently deposited on the modified substrates and thermally annealed to form surface localized MnSiO3 based barrier layers. The energy-dispersive X-ray spectroscopy elemental maps show that the atomic oxygen treatments facilitate the formation of a continuous manganese silicate barrier within dense low-k films, but significant manganese diffusion is observed in the case of porous substrates, negatively impacting the formation of a discrete barrier layer. Ultimately, the atomic oxygen treatment proves effective in modifying the surface of non-porous dielectrics while continuing to facilitate barrier formation. However, in the case of high porosity films, diffusion of manganese into the bulk film remains a critical issue.

9. Damage by radicals and photons during plasma cleaning of porous low-k SiOCH. II. Water uptake and change in dielectric constant

SciTech Connect

Shoeb, Juline; Kushner, Mark J.

2012-07-15

Porous dielectric materials provide lower capacitances that reduce RC time delays in integrated circuits. Typical low-k materials include porous SiOCH-silicon dioxide with carbon groups, principally CH{sub 3}, lining the pores. With a high porosity, internally connected pores provide pathways for reactive species to enter into the material. Fluorocarbon plasmas are often used to etch SiOCH, a process that leaves a fluorocarbon polymer on the surface that must later be removed. During cleaning using Ar/O{sub 2} or He/H{sub 2} plasmas, reactions of radicals that diffuse into the SiOCH and photons that penetrate into the SiOCH can remove -CH{sub 3} groups. Due to its higher reactivity, cleaning with Ar/O{sub 2} plasmas removes more -CH{sub 3} groups than He/H{sub 2} plasmas, and so produce more free radical sites, such as -SiO{sub 2} Bullet (a -SiO{sub 2}-CH{sub 3} site with the -CH{sub 3} group removed).Upon exposure to humid air, these free radical sites can chemisorb H{sub 2}O to form hydrophilic Si-OH which can further physisorb H{sub 2}O through hydrogen bonding to form Si-OH(H{sub 2}O). With the high dielectric constant of water, even a small percentage of water uptake can significantly increase the effective dielectric constant of SiOCH. In this paper, we report on results from a computational investigation of the cleaning of SiOCH using Ar/O{sub 2} or He/H{sub 2} plasmas and subsequent exposure to humid air. The authors found that plasma cleaning with He/H{sub 2} mixtures produce less demethylation than cleaning with Ar/O{sub 2} plasmas, as so results in less water uptake, and a smaller increase in dielectric constant. The water that produces the increase in dielectric constant is roughly half chemisorbed and half physisorbed, the latter of which can be removed with mild heating. Sealing the pores with NH{sub 3} plasma treatment reduces water uptake and helps prevent the increase in dielectric constant.

10. Atmospheric propagation of THz radiation.

SciTech Connect

Wanke, Michael Clement; Mangan, Michael A.; Foltynowicz, Robert J.

2005-11-01

In this investigation, we conduct a literature study of the best experimental and theoretical data available for thin and thick atmospheres on THz radiation propagation from 0.1 to 10 THz. We determined that for thick atmospheres no data exists beyond 450 GHz. For thin atmospheres data exists from 0.35 to 1.2 THz. We were successful in using FASE code with the HITRAN database to simulate the THz transmission spectrum for Mauna Kea from 0.1 to 2 THz. Lastly, we successfully measured the THz transmission spectra of laboratory atmospheres at relative humidities of 18 and 27%. In general, we found that an increase in the water content of the atmosphere led to a decrease in the THz transmission. We identified two potential windows in an Albuquerque atmosphere for THz propagation which were the regions from 1.2 to 1.4 THz and 1.4 to 1.6 THz.

11. Anisotropic terahertz dielectric responses of sodium nitrate crystals.

PubMed

Fu, Xiaojian; Song, Youting; Sun, Changqing; Zhou, Ji

2014-04-21

Terahertz (THz) spectroscopy has become an effective tool to characterize the low-frequency rotational and vibrational modes of molecules. In addition, novel THz dielectric responses and optical properties on the basis of molecular rotation and vibration have attracted lots of attention because of their potential application in THz devices. In this paper, the dielectric response of low-symmetric sodium nitrate crystals in the frequency range of 0.2-1.5 THz was experimentally demonstrated. Four absorption bands at 0.23, 0.47, 0.92, and 1.15 THz were observed in the dielectric spectra and were tentatively ascribed to the rotational motion of nitrate ions. Based on the molecular rotation mechanism, the dielectric anisotropy and dielectric resonance of the crystal were discussed in detail.

12. Correlation between stress-induced leakage current and dielectric degradation in ultra-porous SiOCH low-k materials

SciTech Connect

Wu, C. De Wolf, I.; Li, Y.; Leśniewska, A.; Varela Pedreira, O.; Marneffe, J.-F. de; Ciofi, I.; Verdonck, P.; Baklanov, M. R.; Bömmels, J.; Tőkei, Zs.; Croes, K.

2015-10-28

Stress-Induced Leakage Current (SILC) behavior during the dielectric degradation of ultra-porous SiOCH low-k materials was investigated. Under high voltage stress, SILC increases to a critical value before final hard breakdown. This SILC increase rate is mainly driven by the injected charges and is negligibly influenced by temperature and voltage. SILC is found to be transient and shows a t{sup −1} relaxation behavior, where t is the storage time at low voltages. This t{sup −1} transient behavior, described by the tunneling front model, is caused by both electron charging of neutral defects in the dielectric close to the cathode interface and discharging of donor defects close to the anode interface. These defects have a uniform density distribution within the probed depth range, which is confirmed by the observed flat band voltage shift results collected during the low voltage storage. By applying an additional discharging step after the low voltage storage, the trap energies and spatial distributions are derived. In a highly degraded low-k dielectric, the majority of defects have a trap depth between 3.4 eV and 3.6 eV and a density level of 1 × 10{sup 18 }eV{sup −1 }cm{sup −3}. The relation between the defect density N and the total amount of the injected charges Q is measured to be sub-linear, N ∼ Q{sup 0.45±0.07}. The physical nature of these stress-induced defects is suggested to be caused by the degradation of the Si-O based skeleton in the low-k dielectric.

13. Properties of aqueous solutions in THz frequency range

NASA Astrophysics Data System (ADS)

Cherkasova, O.; Nazarov, M.; Shkurinov, A.

2017-01-01

Terahertz time-domain spectroscopy has been used for measuring of bovine serum albumin and glucose solutions response. The transmission and the attenuated total internal reflection geometries have been combined for analyzing the dielectric properties of aqueous solutions spectra at 0.07-3.2 THz.

14. Microwave and THz sensing using slab-pair-based metamaterials

SciTech Connect

Kenanakis, G.; Shen, Nianhai; Mavidis, Ch.; Katsarakis, N.; Kafesaki, M.; Soukoulis, Costas M.; Economou, E.N.

2012-10-15

In this work the sensing capability of an artificial magnetic metamaterial based on pairs of metal slabs is demonstrated, both theoretically and experimentally, in the microwave regime. The demonstration is based on transmission measurements and simulations monitoring the shift of the magnetic resonance frequency as one changes a thin dielectric layer placed between the slabs of the pairs. Strong dependence of the magnetic resonance frequency on both the permittivity and the thickness of the dielectric layer under detection was observed. The sensitivity to the dielectrics′ permittivity (ε) is larger for dielectrics of low ε values, which makes the approach suitable for sensing organic materials also in the THz regime. The capability of our approach for THz sensing is also demonstrated through simulations.

15. Three-dimensional THz lumped-circuit resonators.

PubMed

Todorov, Yanko; Desfond, Pascal; Belacel, Cherif; Becerra, Loïc; Sirtori, Carlo

2015-06-29

Our work describes a novel three dimensional meta-material resonator design for optoelectronic applications in the THz spectral range. In our resonant circuits, the capacitors are formed by double-metal regions cladding a dielectric core. Unlike conventional planar metamaterials, the electric field is perpendicular to the surface and totally confined in the dielectric core. Furthermore, the magnetic field, confined in the inductive part, is parallel to the electric field, ruling out coupling through propagation effects. Our geometry thus combines the benefit of double-metal structures that provide parallel plate capacitors, while maintaining the ability of meta-material resonators to adjust independently the capacitive and inductive parts. Furthermore, in our geometry, a constant bias can be applied across the dielectric, making these resonators very suitable for applications such as ultra-low dark current THz quantum detectors and amplifiers based on quantum cascade gain medium.

16. THz Local Oscillator Technology

NASA Technical Reports Server (NTRS)

Mehdi, Imran

2004-01-01

The last decade has seen a number of technological advancements that have now made it possible to implement fully solid state local oscillator chains up to 2 THz. These chains are composed of cascaded planar multiplier stages that are pumped with W-band high power sources. The high power W-band sources are achieved by power combining MMIC amplifiers and can provide in access of 150 mW with about 10% bandwidth. Planar diode technology has also enabled novel circuit topologies that can take advantage of the high input power and demonstrate significant efficiencies well into the THz range. Cascaded chains to 1.9 THz have now been demonstrated with enough output power to successfully pump hot-electron bolometer mixers in this frequency range. An overview of the current State-of-the-Art of the local oscillator technology will be presented along with highlighting future trends and challenges.

17. THz Emission Spectroscopy for THz Spintronics

NASA Astrophysics Data System (ADS)

Jarik Huisman, Thomas; Rasing, Theo

2017-01-01

Spintronics is used as the standard for the readout of magnetically stored data and also has commercial applications for writing data. The generation, control and detection of spin-polarized currents, spin-dependent electric transport, and pure spin currents on the subpicosecond (10-12 s) timescale are the next challenges in spintronics. Terahertz (THz, 1012 Hz) emission spectroscopy has proven to be an excellent tool for investigating these challenges. In this short review, we outline the functioning of this spectroscopic technique and its recent applications to spintronics.

18. Pulsed THz spectroscopy of substance under disordered opaque cover

NASA Astrophysics Data System (ADS)

Trofimov, V. A.; Zagursky, D. Yu.; Zakharova, I. G.

2016-02-01

Remote sensing using the pulsed THz-TDS is of great interest because of its possible practical applications. Many ordinary materials (paper, for example) are transparent to THz radiation while the hazardous substances, which have to detect, possess fingerprints in this frequency range. However, cover of ordinary material can distort its spectrum in such a way that the spectrum of reflected THz pulse or transmitted THz pulse will contain absorption frequencies, which are inherent to dangerous substance (explosives, illistic drugs....), despite their absence in the material under consideration. This is a consequence of covering material influence due to its density fluctuation or its structure variation, for example. As rule, covering material structure fluctuation may be comparable with some wavelengths of the probing THz radiation. Thus, the cover can act as a disordered photonic structure with respect to incident THz pulse and its action results in additional absorption spectral lines appearance and in turn, the incorrect substance identification will take place. In this paper we discuss an influence of quasi-periodic structure with variable dielectric constant on the spectrum of a substance, which is placed behind or inside such structure. The investigation is conducted by means of computer simulation. We consider a single layer of optically active substance placed between two covers consisting of linear layers with random dielectric permittivity. Incident Gaussian pulse with a few-cycles falls on the substance covered by layers. Both transmitted pulse and reflected pulse are analyzed and their spectra are compared to those of the incident pulse. For description of a THz pulse interaction with an optically active substance covered by disordered structures we use the Maxwell's equations together with matrix-density formalism. The appearance of additional spectrum extremes due to the layered structure influence is illustrated. Computer simulation results were

19. Low-noise THz MgB2 Josephson mixer

NASA Astrophysics Data System (ADS)

Cunnane, Daniel; Kawamura, Jonathan H.; Acharya, Narendra; Wolak, Matthäus A.; Xi, X. X.; Karasik, Boris S.

2016-09-01

The potential applications for high frequency operation of the Josephson effect in MgB2 include THz mixers, direct detectors, and digital circuits. Here we report on MgB2 weak links which exhibit the Josephson behavior up to almost 2 THz and using them for low-noise heterodyne detection of THz radiation. The devices are made from epitaxial film grown in the c-axis direction by the hybrid physical-chemical vapor deposition method. The current in the junctions travels parallel to the surface of the film, thus making possible a large contribution of the quasi-two-dimensional σ-gap in transport across the weak link. These devices are connected to a planar spiral antenna with a dielectric substrate lens to facilitate coupling to free-space radiation for use as a detector. The IcRn product of the junction is 5.25 mV, giving confirmation of a large gap parameter. The sensitivity of the mixer was measured from 0.6 THz to 1.9 THz. At a bath temperature of over 20 K, a mixer noise temperature less than 2000 K (DSB) was measured near 0.6 THz.

20. A single dielectric nanolaser

NASA Astrophysics Data System (ADS)

Huang, Tsung-Yu; Yen, Ta-Jen

2016-09-01

To conquer Ohmic losses from metal and enhance pump absorption efficiency of a nanolaser based on surface plasmon polariton, we theoretically calculate the first magnetic and electric scattering coefficient of a dielectric sphere under a plane wave excitation with a dielectric constant of around 12. From this calculation, we could retrieve both negative effective permittivity and permeability of the sphere simultaneously at frequencies around 153 THz in the aids of Lewin's theory and the power distribution clearly demonstrate the expected negative Goos-Hänchen effect, which usually occurred in a negative refractive waveguide, thus creating two energy vortices to trap incident energy and then promoting the pump absorption efficiency. Meanwhile, a magnetic lasing mode at 167.3 THz is demonstrated and reveals a magnetic dipole resonance mode and a circulating energy flow within the dielectric sphere, providing a possible stopped light feedback mechanism to enable the all-dielectric nanolaser. More importantly, the corresponding mode volume is reduced to 0.01λ3 and a gain threshold of 5.1×103 is obtained. To validate our design of all-dielectric nanolaser, we employ finite-difference-time-domain simulation software to examine the behavior of the nanolaser. From simulation, we could obtain a pinned-down population inversion of 0.001 and a lasing peak at around 166.5 THz, which is very consistent with the prediction of Mie theory. Finally, according to Mie theory, we can regard the all-dielectric nanolaser as the excitation of material polariton and thus could make an analogue between lasing modes of the dielectric and metallic nanoparticles.

1. Model of THz Magnetization Dynamics

PubMed Central

Bocklage, Lars

2016-01-01

Magnetization dynamics can be coherently controlled by THz laser excitation, which can be applied in ultrafast magnetization control and switching. Here, transient magnetization dynamics are calculated for excitation with THz magnetic field pulses. We use the ansatz of Smit and Beljers, to formulate dynamic properties of the magnetization via partial derivatives of the samples free energy density, and extend it to solve the Landau-Lifshitz-equation to obtain the THz transients of the magnetization. The model is used to determine the magnetization response to ultrafast multi- and single-cycle THz pulses. Control of the magnetization trajectory by utilizing the THz pulse shape and polarization is demonstrated. PMID:26956997

2. Electromigration failure mode concerning negative resistance shift of Cu interconnects buried in porous low-k dielectric

NASA Astrophysics Data System (ADS)

Zheng, Hui; Yin, Binfeng; Yu, Hewei; Chen, Leigang; Gao, Lin; Zhou, Ke; Kuo, Chinte

2017-02-01

Electromigration failure mode concerning a negative resistance shift of 4%-11% and cathode burnout was reported for Cu interconnects buried in porous low-k in this paper. Evidence for oxidation and debonding of Ta/TaN liner at high temperature was revealed, which was demonstrated to have been enabled by the unsealed porous low-k due to moisture uptake. The cathode burnout was thus attributed to severe Joule heating induced in the insulated liner after oxidation. The resistance decay of Cu also exhibited to be mainly consistent with the calculation from specularity recovery of electron scattering at the Cu/Ta interface after oxidation and debonding of the liner, although other factors like strain relaxation may also have some contribution.

3. Optimal Super Dielectric Material

DTIC Science & Technology

2015-09-01

electrically insulating materials filled to the point of incipient wetness (paste consistency) with liquids containing dissolved ions. This work...109. This strongly supports the fundamental hypothesis of SDM: In the presence of an electric field any electrically insulating, porous material...ABSTRACT The results of this study establish that powder-based super dielectric materials (SDM) are a large family of porous electrically

4. Coherent Cherenkov radiation as an intense THz source

NASA Astrophysics Data System (ADS)

Bleko, V.; Karataev, P.; Konkov, A.; Kruchinin, K.; Naumenko, G.; Potylitsyn, A.; Vaughan, T.

2016-07-01

Diffraction and Cherenkov radiation of relativistic electrons from a dielectric target has been proposed as mechanism for production of intense terahertz (THz) radiation. The use of an extremely short high-energy electron beam of a 4th generation light source (X-ray free electron laser) appears to be very promising. A moderate power from the electron beam can be extracted and converted into THz radiation with nearly zero absorption losses. The initial experiment on THz observation will be performed at CLARA/VELA FEL test facility in the UK to demonstrate the principle to a wider community and to develop the radiator prototype. In this paper, we present our theoretical predictions (based on the approach of polarization currents), which provides the basis for interpreting the future experimental measurements. We will also present our hardware design and discuss a plan of the future experiment.

5. 3D THz hyperspectrum applied in security check-in

NASA Astrophysics Data System (ADS)

Damian, V.; Logofǎtu, P. C.; Vasile, T.

2016-12-01

We developed a measuring technology using a TDS-THz system to construct hyperspectral images of some objects, including hazardous materials. "T-rays" (the THz spectral domain of the light) have a growing importance in security and imagistic domain. Due to their property of penetrating through dielectric objects, and using non-ionizing radiations, the THz systems have become a standard for "hot-places" (airports, train stations etc.). The hyperspectral images are 3D images having 2D spatial dimension and one spectral dimension. In this way, we obtain simultaneously information about the form of the object and its molecular composition. For discriminating between substances, we must first build a database of spectra for hazardous and dangerous substances. We experiment our system on some items (among them a firecracker, a cigarette and a metal collar) and we tried to discriminate between them using the database of spectra.

6. Terahertz wire grid polarizer fabricated by imprinting porous silicon.

PubMed

Imakita, Kenji; Kamada, Takeshi; Fujii, Minoru; Aoki, Kanna; Mizuhata, Minoru; Hayashi, Shinji

2013-12-01

A terahertz (THz) wire-grid polarizer is fabricated by imprinting porous Si followed by oblique evaporation of Ag. We demonstrate that it works in a wide frequency region covering from 5 to 18 THz with the extinction ratio of 10 dB. The frequency region is much wider than that of THz wire-grid polarizers fabricated by conventional imprint lithography using organic materials. The result suggests that imprinting of porous Si is a promising fabrication technique to realize low-cost wire-grid polarizers working in the THz region.

7. In Situ Synthesis of Porous Carbons by Using Room-Temperature, Atmospheric-Pressure Dielectric Barrier Discharge Plasma as High-Performance Adsorbents for Solid-Phase Microextraction.

PubMed

Lin, Yao; Wu, Li; Xu, Kailai; Tian, Yunfei; Hou, Xiandeng; Zheng, Chengbin

2015-09-21

A one-step, template-free method is described to synthesize porous carbons (PCs) in situ on a metal surface by using a room-temperature, atmospheric-pressure dielectric barrier discharge (DBD) plasma. This method not only features high efficiency, environmentally friendliness, and low cost and simple equipment, but also can conveniently realize large-area synthesis of PCs by only changing the design of the DBD reactor. The synthesized PCs have a regulated nestlike morphology, and thus, provide a high specific surface area and high pore volume, which result in excellent adsorption properties. Its applicability was demonstrated by using a PC-coated stainless-steel fiber as a solid-phase microextraction (SPME) fiber to preconcentrate polycyclic aromatic hydrocarbons (PAHs) prior to analysis by gas chromatography with flame ionization detection (GC-FID). The results showed that the fiber exhibited excellent enrichment factors (4.1×10(4) to 3.1×10(5)) toward all tested PAHs. Thus, the PC-based SPME-GC-FID provides low limits of detection (2 to 20 ng L(-1)), good precision (<7.8%), and good recoveries (80-115%) for ultra-sensitive determination of PAHs in real water samples. In addition, the PC-coated fiber could be stable enough for more than 500 replicate extraction cycles.

8. THz channel characterization for future wireless gigabit indoor communication systems

NASA Astrophysics Data System (ADS)

Piesiewicz, Radoslaw; Jemai, Jaouhar; Koch, Martin; Kurner, Thomas

2005-03-01

Short range wireless communication systems are expanding at rapid rate, finding application in offices, congested urban areas and homes. Development of wireless local area networks is accompanied by a steady increase in the demand for ever higher data rates. This in turn entails the necessity to develop communication systems which operate at higher frequencies. Currently WLAN works at a few GHz, while systems operating at several ten GHz appear already feasible. It can be expected that wireless short-range communication networks will soon push towards the THz frequency range and that systems which handle high-density information and support wider bandwidth communications will be developed in a few years time. Since THz radiation is strongly absorbed by the atmosphere, working distances may be short and individual THz pico-cells may cover only single rooms or at most one building. For an indoor system of practical importance it must be robust against shadowing. Recently, flexible all-plastic mirrors, supporting specular reflections in the THz range have been demonstrated. They are cheap and easy to produce and can be used as frequency selective wall-paper to enhance the reflectivity of walls and hence facilitate non-line-of-sight communication in a THz cell. For this case the spatial and temporal characteristics of the indoor THz propagation channel in a room with randomly placed objects and moving people are derived with ray-tracing methodology and Monte Carlo simulations. Our simulations show that high-gain antennas will be needed for the realization of THz communication in indoor environments. Furthermore, indirect transmission paths between transmitter and receiver, supported by dielectric mirrors make the communication channel much more robust against shadowing.

9. Quantitative study of rectangular waveguide behavior in the THz.

SciTech Connect

Rowen, Adam M.; Nordquist, Christopher Daniel; Wanke, Michael Clement

2009-10-01

This report describes our efforts to quantify the behavior of micro-fabricated THz rectangular waveguides on a configurable, robust semiconductor-based platform. These waveguides are an enabling technology for coupling THz radiation directly from or to lasers, mixers, detectors, antennas, and other devices. Traditional waveguides fabricated on semiconductor platforms such as dielectric guides in the infrared or co-planar waveguides in the microwave regions, suffer high absorption and radiative losses in the THz. The former leads to very short propagation lengths, while the latter will lead to unwanted radiation modes and/or crosstalk in integrated devices. This project exploited the initial developments of THz micro-machined rectangular waveguides developed under the THz Grand Challenge Program, but instead of focusing on THz transceiver integration, this project focused on exploring the propagation loss and far-field radiation patterns of the waveguides. During the 9 month duration of this project we were able to reproduce the waveguide loss per unit of length in the waveguides and started to explore how the loss depended on wavelength. We also explored the far-field beam patterns emitted by H-plane horn antennas attached to the waveguides. In the process we learned that the method of measuring the beam patterns has a significant impact on what is actually measured, and this may have an effect on most of the beam patterns of THz that have been reported to date. The beam pattern measurements improved significantly throughout the project, but more refinements of the measurement are required before a definitive determination of the beam-pattern can be made.

10. Corrugated capillary as THz Cherenkov Smith-Purcell radiator

NASA Astrophysics Data System (ADS)

Lekomtsev, K. V.; Aryshev, A. S.; Tishchenko, A. A.; Ponomarenko, A. A.; Sukharev, V. M.; Terunuma, N.; Urakawa, J.; Strikhanov, M. N.

2016-07-01

In this article we discussed Particle In Cell electromagnetic simulations and mechanical design of dielectric capillaries that produce THz Cherenkov Smith-Purcell radiation (ChSPR), arising when a femtosecond electron multi-bunch beam propagates through corrugated and non-corrugated dielectric capillaries with metallic radiation reflectors. We investigated the influence of the four-bunch beam on the SPR field spectrum and on the ChSPR power spectrum, and the influence of the non-central beam propagation on the ChSPR power spectrum. We also discussed the design and assembly of the capillaries, constructed as sets of cylindrical rings.

11. A review on the sub-THz/THz gyrotrons

NASA Astrophysics Data System (ADS)

Kumar, Nitin; Singh, Udaybir; Bera, Anirban; Sinha, A. K.

2016-05-01

A review on the sub-THz/THz gyrotrons is performed in this manuscript. The present development status of gyrotrons can be divided into three streams for the sake of better understanding: 1. low frequency (<35 GHz), medium power (<100 kW), small size and easy to handle gyrotrons for industrial applications, 2. very high power (1 MW or more), medium frequency (100-200 GHz) gyrotrons for plasma fusion applications, 3. low power (few tens of watt to kW), high frequency (>200 GHz) gyrotrons for various innovative applications. In this manuscript, the third stream of gyrotron development is reviewed. In last few decades several innovative applications are searched in sub-THz/THz band where the gyrotrons could be used as an efficient source of RF radiation. The applications of sub-THz/THz gyrotrons including the futuristic scope of the device are also discussed in this article. Further, several criticalities arise in the design and development when the gyrotron operation shifts toward the high frequency band. Various such design and technological challenges are also discussed here. Finally the development status of sub-THz/THz gyrotrons as per the use in various scientific and technological applications is also discussed.

12. THz Imaging of Skin Burn: Seeing the Unseen—An Overview

PubMed Central

Dutta, Moumita; Bhalla, Amar S.; Guo, Ruyan

2016-01-01

Significance: This review article puts together all the studies performed so far in realizing terahertz (THz) spectra as a probing mechanism for burn evaluation, summarizing their experimental conditions, observations, outcomes, merits, and demerits, along with a comparative discussion of other currently used technologies to present the state of art in a condensed manner. The key features of this noncontact investigation technique like its precise burn depth analysis and the approaches it follows to convert the probed data into a quantitative measure have also been discussed in this article. Recent Advances: The current research developments in THz regime observed in device design technologies (like THz time domain spectrometer, quantum cascade THz lasers, THz single-photon detectors, etc.) and in understanding its unique properties (like nonionizing nature, penetrability through dry dielectrics, etc.) have motivated the research world to realize THz window as a potential candidate for burn detection. Critical Issues: Application of appropriate medical measure for burn injury is primarily subjective to proper estimation of burn depth. Tool modality distinguishing between partial and full-thickness burn contributing toward correct medical care is indeed awaited. Future Directions: The overview of THz imaging as a burn assessment tool as provided in this article will certainly help in further nurturing of this emerging diagnostic technique particularly in improving its detection and accompanied image processing methods so that the minute nuances captured by the THz beam can be correlated with the physiological–anatomical changes in skin structures, caused by burn, for better sensitivity, resolution, and quantitative analysis. PMID:27602253

13. Exploration of the effects of burn parameters on THz wound imaging

NASA Astrophysics Data System (ADS)

Bajwa, Neha; Sung, Shijun; Fishbein, Michael; Grundfest, Warren S.; Taylor, Zachary D.

2015-08-01

The high contrast resolution afforded by terahertz (1 THz = 1012 Hz) imaging of physiologic tissue continues to drive explorations into the utility of THz technology for burn wound detection. Although we have previously reported the use of a novel, reflective THz imaging technology to sense spatiotemporal differences in reflectivity between partial and full thickness burn wounds, no evidence exists of a one-to-one correlation between structural damage observed in histological assessments of burn severity and THz signal. For example, varying burn induction methods may all result in a common burn wound severity, however, burn features observed in parallel THz imagery may not be identical. Successful clinical translation of THz technology as a comprehensive burn guidance tool, therefore, necessitates an understanding of THz signal and its relation to wound pathophysiology. In this work, longitudinal THz imagery was acquired with a quartz (n = 2.1, 500 μm) window of cutaneous wounds induced with the same brand geometry and contact pressure but varying contact times (5, 7, and 10 seconds) in in vivo, pre-clinical rat models (n=3) over a period of 3 days. Though all burn wounds were evaluated to be deep partial thickness with histology, THz contrasts observed for each burn contact time were intrinsically unique. This is the first preliminary in vivo evidence of a many-to-one relationship between changes in THz contrast and burn severity as ascertained by histology. Future large-scale studies are required to assess whether these observed changes in THz contrast may be interpreted as physiological changes occurring over time, morphometric changes related to anatomical change, or electromagnetic changes between dielectric substrate windows and the underlying tissue.

14. THz stark spectroscopy (Conference Presentation)

NASA Astrophysics Data System (ADS)

Feurer, Thomas; Rohwer, Egmont; Akbarimoosavi, Maryam

2016-09-01

Stark spectroscopy has been pioneered many decades ago and is a unique tool to extract information on molecular constants such as changes of dipole moments or polarizabilities upon excitation. Here we introduce a new twist, i.e. THz Stark spectroscopy. In THz fields the electric field vector oscillates on time scales of picoseconds and thus much faster than in conventional Stark spectroscopy. It therefore may allow to distinguish between different electric field contributions by analyzing the dynamics of the THz response. We first demonstrate that conventional THz sources can be boosted by combination with field enhancement structures, reaching field strength of GV/m driving several different materials into the nonlinear response regime. Then we discuss THz fields influencing charge transfer in different molecules.

15. Optically-electrically pumped THz source

NASA Astrophysics Data System (ADS)

Haji-Saeed, Bahareh; Khoury, Jed; Buchwald, Walter; Woods, Charles; Wentzell, Sandra; Krejca, Brian; Kierstead, John

2010-08-01

In this paper, we propose a design for a widely tunable solid-state optically and electrically pumped THz source based on the Smith-Purcell free-electron laser. Our design consists of a thin dielectric layer sandwiched between an upper corrugated structure and a lower layer of thin metal, semiconductor, or high electron mobility material. The lower layer is for current streaming, which replaces the electron beam in the Smith-Purcell free-electron laser design. The upper layer consists of two micro-gratings for optical pumping, and a nano-grating to couple with electrical pumping in the lower layer. The optically generated surface plasmon waves from the upper layer and the electrically induced surface plasmon waves from the lower layer are then coupled. Emission enhancement occurs when the plasmonic waves in both layers are resonantly coupled.

16. High Absorptance Coatings for THz Applications

NASA Technical Reports Server (NTRS)

Wollack, Edward J.

2012-01-01

High absorptance materials find application throughout the electromagnetic spectrum as radiation terminations, calibration standards, and glint reduction coatings. Successful use of materials at millimeter through submillimeter wavelengths requires an accurate knowledge and control over their thermal, mechanical, and electromagnetic properties in order to achieve the desired response while minimizing mass and volume. In practice, the achieved blackness is intimately linked to the material properties and geometry. Here, we summarize the characteristics of a variety of tunable artificial dielectric mixtures appropriate for THz applications at room and cryogenic temperatures. Theoretical guidelines for their application will be provided in the context of the effective-medium mean-field-approximation. The performance of these coatings as elements of reflectance standards, radiometric flux calibrators, passive thermal radiators, and stray light suppression baffles for imaging systems will be reviewed.

17. THz Spectroscopy of the Atmosphere

NASA Technical Reports Server (NTRS)

Pickett, Herbert M.

2000-01-01

THz spectroscopy of the atmosphere has been driven by the need to make remote sensing measurements of OH. While the THz region can be used for sensitive detection on many atmospheric molecules, the THz region is the best region for measuring the diurnal behavior of stratospheric OH by remote sensing. The infrared region near 3 microns suffers from chemiluminescence and from spectral contamination due to water. The ultraviolet region near 300 nm requires solar illumination. The three techniques for OH emission measurements in the THz region include Fourier Transform interferometry, Fabry-Perot interferometry, and heterodyne radiometry. The first two use cryogenic direct detectors while the last technique uses a local oscillator and a mixer to down convert the THz signal to GHz frequencies. All techniques have been used to measure stratospheric OH from balloon platforms. OH results from the Fabry-Perot based FILOS instrument will be given. Heterodyne measurement of OH at 2.5 THz has been selected to be a component of the Microwave Limb Sounder on the Earth Observing System CHEM-1 polar satellite. The design of this instrument will be described. A balloon-based prototype heterodyne 2.5 THz radiometer had its first flight on, 24 May 1998. Results form this flight will be presented.

18. THz spectroscopy of the atmosphere

NASA Astrophysics Data System (ADS)

Pickett, Herbert M.

1999-04-01

THz spectroscopy of the atmosphere has been driven by the need to make remote sensing measurements of OH. While the THz region can be used for sensitive detection on many atmospheric molecules, the THz region is the best region for measuring the diurnal behavior of stratospheric OH by remote sensing.THe IR region near 3 micrometers requires solar illumination. The three techniques for OH emission measurements in the THz region include Fourier Transform interferometry, Fabry-Perot interferometry, and heterodyne radiometry. The first two use cryogenic direct detectors while the last technique uses a local oscillator and a mixer to down convert the THz signal to GHz frequencies. All techniques have been used to measure stratospheric OH from balloon platforms. OH result from the Fabry-Perot based FILOS instrument will be given. Heterodyne measurement of OH at 2.5 THz has been selected to be a component of the microwave limb sounder on the Earth Observing System CHEM-1 polar satellite. The design of this instrument will be described. A balloon-based prototype heterodyne 2.5 THz radiometer had its first flight on 24 May 1998. Results from this flight will be presented.

19. Sapphire decelerating capillary channel integrated with antenna at frequency 0.675 THz

NASA Astrophysics Data System (ADS)

Ashanin, I. A.; Polozov, S. M.

2016-07-01

In recent years, there has been an increasing interest in THz-radiation for application in medicine (THz tomographs), in pharmaceutics (composition analysis for medicines), in introscopy of large-scale objects (ships, trains, containers) and others. THz-radiation can be generated by relativistic electron bunches passing through the Cherenkov decelerating capillary channel (circular waveguide with dielectric filling) with horn extraction. Relativistic electron beams having ∼100 µm in diameter and pulse durations of 1 ps or less (as in photoinjectors) are capable of producing substantial power of THz-radiation. High-peak power coherent Cherenkov radiation can be produced by a properly modulated high-brightness electron beam or by a single, high-density bunch having sub-wavelength dimension. The aperture of a Cherenkov decelerating structure should be comparable with the mm or sub-mm wavelength (0.1-3 mm). Different dielectric materials for the internal surface coating of the capillary channel of mm-sub-mm cross-section can be used. As is known, a frequency of 0.675 THz corresponds to the atmospheric window with high transparency. This report presents the results of electrodynamics study of the metallized sapphire decelerating Cherenkov capillary. A horn antenna attached to the metallized sapphire capillary channel at the 0.675 THz resonant frequency will be considered.

20. THz-metamaterial absorbers

NASA Astrophysics Data System (ADS)

Tuong Pham, Van; Park, J. W.; Vu, Dinh Lam; Zheng, H. Y.; Rhee, J. Y.; Kim, K. W.; Lee, Y. P.

2013-03-01

An ultrabroad-band metamaterial absorber was investigated in mid-IR regime based on a similar model in previous work. The high absorption of metamaterial was obtained in a band of 8-11.7 THz with energy loss distributed in SiO2, which is appropriate potentially for solar-cell applications. A perfect absorption peak was provided by using a sandwich structure with periodical anti-dot pattern in the IR region, getting closed to visible-band metamaterials. The dimensional parameters were examined for the corresponding fabrication. Invited talk at the 6th International Workshop on Advanced Materials Science and Nanotechnology, 30 October-2 November, 2012, Ha Long, Vietnam.

1. Surface plasmon-polariton resonance at diffraction of THz radiation on semiconductor gratings

NASA Astrophysics Data System (ADS)

Spevak, I. S.; Kuzmenko, A. A.; Tymchenko, M.; Gavrikov, V. K.; Shulga, V. M.; Feng, J.; Sun, H. B.; Kamenev, Yu. E.; Kats, A. V.

2016-08-01

Resonance diffraction of THz hidrogen cyanide laser radiation on a semiconductor (InSb) grating is studied both experimentally and theoretically. The specular reflectivity suppression due to the resonance excitation of the THz surface plasmon-polariton is observed on a pure semiconductor grating and on semiconductor gratings covered with a thin dielectric layer. The dielectric coating of the grating results in the resonance shift and widening depending both on the layer thickness and dielectric properties. A simple analytical theory of the resonance diffraction on rather shallow gratings covered with a dielectric layer is presented, and the results are in a good accordance with the experimental data. Analytical expressions for the resonance shift and broadening are essential for the resonance properties understanding and useful for sensing data interpretation of the agents deposited on the grating surface.

2. GHz-THz Electronics

DTIC Science & Technology

2013-03-07

Material and device breakthroughs for meta-materials, artificial dielectrics, ferrites , multi-ferroics, nano-magnetics, and micro/nano...deposition, atomic layer deposition promises monolayer control without metal catalyst In fra re d Tr an sm is si on (% ) C B N 8 Distribution A

3. Compact High Power THz Source

SciTech Connect

Geoffrey Krafft

2003-08-01

In this paper a new type of THz radiation source, based on recirculating an electron beam through a high gradient superconducting radio frequency cavity, and using this beam to drive a standard electromagnetic undulator, is discussed. Because the beam is recirculated, short bunches may be produced that radiate coherently in the undulator, yielding high average THz power for relatively low average beam power. Deceleration from the coherent emission, and the detuning it causes is discussed.

4. Terahertz dielectric response of photoexcited carriers in Si revealed via single-shot optical-pump and terahertz-probe spectroscopy

SciTech Connect

Minami, Yasuo; Horiuchi, Kohei; Masuda, Kaisei; Takeda, Jun; Katayama, Ikufumi

2015-10-26

We have demonstrated accurate observations of terahertz (THz) dielectric response due to photoexcited carriers in a Si plate via single-shot optical-pump and THz-probe spectroscopy. In contrast to conventional THz time-domain spectroscopy, this spectroscopic technique allows single-shot detection of the THz response of materials at a given delay time between the pump and THz pulses, thereby sufficiently extending the time interval between the pump pulses. As a result, we can accurately measure the dielectric properties of materials, while avoiding artifacts in the response caused by the accumulation of long-lived photoexcited carriers. Using our single-shot scheme, the transmittance of a Si plate was measured in the range of 0.5–2.5 THz with different pump fluences. Based on a Drude model analysis, the optically induced complex dielectric constant, plasma frequency, and damping rate in the THz region were quantitatively evaluated.

5. THz Local Oscillator Sources

NASA Astrophysics Data System (ADS)

Mehdi, Imran; Schlecht, Erich; Chattopadhyay, Goutam; Siegel, Peter H.

Most operational Submillimeter-wave radio telescopes, both space borne and ground based, employ local oscillator sources based on Gunn diodes followed by whisker contacted Schottky multipliers. Enough progress, however, has been made on a number of fronts to conclude that next generation of radio telescopes that become operational in the new Millennium will have a different local oscillator (LO) generation architecture. MMIC power amplifiers with impressive gain in the Ka- to-W band have enabled the use of microwave synthesizers which can then be actively multiplied to provide a frequency agile power source beyond 100 GHz. This medium power millimeter source can then be amplified to enable efficient pumping of follow-on balanced multiplier stages. Input power to the multipliers can be further enhanced by power combining to achieve close to half a Watt at W-band. An 800 GHz three-stage multiplier chain, implemented this way has demonstrated a peak output power of 1 mW. A second advance in LO generation lies in the Schottky diode varactor technology. Planar Schottky diode multipliers have now been demonstrated up to 1500 GHz and it can be assumed that most of the future multiplier chains will be based on these robust devices rather than the whisker contacted diode of the past. The ability to produce planar GaAs diode chips deep into the THz range, with submicron dimensions, has opened up a wide range of circuit design space which can be taken advantage of to improve efficiency, bandwidth, and power handling capability of the multipliers. A third breakthrough has been the demonstration of photonic based LO sources utilizing GaAs photomixers. These sources, though not yet implemented in robust space borne missions, offer a number of advantages over their electronic counterparts, including extremely broad tuning, fiber coupled components, and solid-state implementation. Another development, which holds some promise, is the use of micro-machining technology to implement

6. Single-layer graphene-assembled 3D porous carbon composites with PVA and Fe₃O₄ nano-fillers: an interface-mediated superior dielectric and EMI shielding performance.

PubMed

Rao, B V Bhaskara; Yadav, Prasad; Aepuru, Radhamanohar; Panda, H S; Ogale, Satishchandra; Kale, S N

2015-07-28

In this study, a novel composite of Fe3O4 nanofiller-decorated single-layer graphene-assembled porous carbon (SLGAPC) with polyvinyl alcohol (PVA) having flexibility and a density of 0.75 g cm(-3) is explored for its dielectric and electromagnetic interference (EMI) response properties. The composite is prepared by the solution casting method and its constituents are optimized as 15 wt% SLGAPC and 20 wt% Fe3O4 through a novel solvent relaxation nuclear magnetic resonance experiment. The PVA-SLGAPC-Fe3O4 composite shows high dielectric permittivity in the range of 1 Hz-10 MHz, enhanced by a factor of 4 as compared to that of the PVA-SLGAPC composite, with a reduced loss by a factor of 2. The temperature dependent dielectric properties reveal the activation energy behaviour with reference to the glass transition temperature (80 °C) of PVA. The dielectric hysteresis with the temperature cycle reveals a remnant polarization. The enhanced dielectric properties are suggested to be the result of improvement in the localized polarization of the integrated interface system (Maxwell-Wagner-Sillars (MWS) polarization) formed by the uniform adsorption of Fe3O4 on the surface of SLGAPC conjugated with PVA. The EMI shielding property of the composite with a low thickness of 0.3 mm in the X-band (8.2-12.4 GHz) shows a very impressive shielding efficiency of ∼15 dB and a specific shielding effectiveness of 20 dB (g cm(-3))(-1), indicating the promising character of this material for flexible EMI shielding applications.

7. Frequency Selective Surface Based Bandpass Filter for THz Communication System

NASA Astrophysics Data System (ADS)

Das, Subrata; Reza, Khan Mamun; Habib, Md. Ahsan

2012-11-01

In this work, a band pass filter based on frequency selective surface (FSS) is presented. The resonance of the FSS is achieved by perforating slot type ring structure on an Aluminum layer. To ensure adequate mechanical strength, this structure is again supported by a dielectric layer. The physical dimensions of the FSS, i.e. ring radius, slot width, cell dimension and width of the layers all are responsible for the resonance behavior. In its electrical equivalent circuit, these dimensions act as inductor and capacitor. The center frequency of the designed filter is at 0.16 THz with a -3 dB bandwidth of 18 GHz. This filter can be utilized as a part of any THz communication system to achieve application specific frequency discrimination. The simulation has been carried by using commercial software-CST Microwave Studio. The performance of the fabricated FSS is evaluated by Microwave Vector Network Analyzer.

8. Monolithic THz Frequency Multipliers

NASA Technical Reports Server (NTRS)

Erickson, N. R.; Narayanan, G.; Grosslein, R. M.; Martin, S.; Mehdi, I.; Smith, P.; Coulomb, M.; DeMartinez, G.

2001-01-01

Frequency multipliers are required as local oscillator sources for frequencies up to 2.7 THz for FIRST and airborne applications. Multipliers at these frequencies have not previously been demonstrated, and the object of this work was to show whether such circuits are really practical. A practical circuit is one which not only performs as well as is required, but also can be replicated in a time that is feasible. As the frequency of circuits is increased, the difficulties in fabrication and assembly increase rapidly. Building all of the circuit on GaAs as a monolithic circuit is highly desirable to minimize the complexity of assembly, but at the highest frequencies, even a complete monolithic circuit is extremely small, and presents serious handling difficulty. This is compounded by the requirement for a very thin substrate. Assembly can become very difficult because of handling problems and critical placement. It is very desirable to make the chip big enough to that it can be seen without magnification, and strong enough that it may be picked up with tweezers. Machined blocks to house the chips present an additional challenge. Blocks with complex features are very expensive, and these also imply very critical assembly of the parts. It would be much better if the features in the block were as simple as possible and non-critical to the function of the chip. In particular, grounding and other electrical interfaces should be done in a manner that is highly reproducible.

9. Electrodynamic model of the field effect transistor application for THz/subTHz radiation detection: Subthreshold and above threshold operation

SciTech Connect

Dobrovolsky, V.

2014-10-21

Developed in this work is an electrodynamic model of field effect transistor (FET) application for THz/subTHz radiation detection. It is based on solution of the Maxwell equations in the gate dielectric, expression for current in the channel, which takes into account both the drift and diffusion current components, and the equation of current continuity. For the regimes under and above threshold at the strong inversion the response voltage, responsivity, wave impedance, power of ohmic loss in the gate and channel have been found, and the electrical noise equivalent power (ENEP) has been estimated. The responsivity is orders of magnitude higher and ENEP under threshold is orders of magnitude less than these values above threshold. Under the threshold, the electromagnetic field in the gate oxide is identical to field of the plane waves in free-space. At the same time, for strong inversion the charging of the gate capacitance through the resistance of channel determines the electric field in oxide.

10. CVD Diamond Dielectric Accelerating Structures

SciTech Connect

Schoessow, P.; Kanareykin, A.; Gat, R.

2009-01-22

The electrical and mechanical properties of diamond make it an ideal candidate material for use in dielectric accelerating structures: high RF breakdown field, extremely low dielectric losses and the highest available thermoconductive coefficient. Using chemical vapor deposition (CVD) cylindrical diamond structures have been manufactured with dimensions corresponding to fundamental TM{sub 01} mode frequencies in the GHz to THz range. Surface treatments are being developed to reduce the secondary electron emission (SEE) coefficient below unity to reduce the possibility of multipactor. The diamond CVD cylindrical waveguide technology developed here can be applied to a variety of other high frequency, large-signal applications.

11. THz Dynamic Nuclear Polarization NMR

PubMed Central

Nanni, Emilio A.; Barnes, Alexander B.; Griffin, Robert G.; Temkin, Richard J.

2013-01-01

Dynamic nuclear polarization (DNP) increases the sensitivity of nuclear magnetic resonance (NMR) spectroscopy by using high frequency microwaves to transfer the polarization of the electrons to the nuclear spins. The enhancement in NMR sensitivity can amount to a factor of well above 100, enabling faster data acquisition and greatly improved NMR measurements. With the increasing magnetic fields (up to 23 T) used in NMR research, the required frequency for DNP falls into the THz band (140–600 GHz). Gyrotrons have been developed to meet the demanding specifications for DNP NMR, including power levels of tens of watts; frequency stability of a few megahertz; and power stability of 1% over runs that last for several days to weeks. Continuous gyrotron frequency tuning of over 1 GHz has also been demonstrated. The complete DNP NMR system must include a low loss transmission line; an optimized antenna; and a holder for efficient coupling of the THz radiation to the sample. This paper describes the DNP NMR process and illustrates the THz systems needed for this demanding spectroscopic application. THz DNP NMR is a rapidly developing, exciting area of THz science and technology. PMID:24639915

12. Coherent THz Pulses from Linear Accelerators

SciTech Connect

G.L. Carr; H. Loos; J.B. Murphy; T. Shaftan; B. Sheehy; X.-J. Wang; W.R. McKinney; M.C. Martin; G.P. Williams; K. Jordan; G. Neil

2003-10-01

Coherent THz pulses are being produced at several facilities using relativistic electrons from linear accelerators. The THz pulses produced at the Brookhaven accelerator have pulse energies exceeding 50 {micro}J and reach a frequency of 2 THz. The high repetition rate of the Jefferson Lab accelerator leads to an average THz power of 20 watts. Possible uses for these high power pulses are discussed.

13. Antiferromagnetic THz-frequency Josephson-like Oscillator Driven by Spin Current

PubMed Central

Khymyn, Roman; Lisenkov, Ivan; Tiberkevich, Vasyl; Ivanov, Boris A.; Slavin, Andrei

2017-01-01

The development of compact and tunable room temperature sources of coherent THz-frequency signals would open a way for numerous new applications. The existing approaches to THz-frequency generation based on superconductor Josephson junctions (JJ), free electron lasers, and quantum cascades require cryogenic temperatures or/and complex setups, preventing the miniaturization and wide use of these devices. We demonstrate theoretically that a bi-layer of a heavy metal (Pt) and a bi-axial antiferromagnetic (AFM) dielectric (NiO) can be a source of a coherent THz signal. A spin-current flowing from a DC-current-driven Pt layer and polarized along the hard AFM anisotropy axis excites a non-uniform in time precession of magnetizations sublattices in the AFM, due to the presence of a weak easy-plane AFM anisotropy. The frequency of the AFM oscillations varies in the range of 0.1–2.0 THz with the driving current in the Pt layer from 108 A/cm2 to 109 A/cm2. The THz-frequency signal from the AFM with the amplitude exceeding 1 V/cm is picked up by the inverse spin-Hall effect in Pt. The operation of a room-temperature AFM THz-frequency oscillator is similar to that of a cryogenic JJ oscillator, with the energy of the easy-plane magnetic anisotropy playing the role of the Josephson energy. PMID:28262731

14. Antiferromagnetic THz-frequency Josephson-like Oscillator Driven by Spin Current

NASA Astrophysics Data System (ADS)

Khymyn, Roman; Lisenkov, Ivan; Tiberkevich, Vasyl; Ivanov, Boris A.; Slavin, Andrei

2017-03-01

The development of compact and tunable room temperature sources of coherent THz-frequency signals would open a way for numerous new applications. The existing approaches to THz-frequency generation based on superconductor Josephson junctions (JJ), free electron lasers, and quantum cascades require cryogenic temperatures or/and complex setups, preventing the miniaturization and wide use of these devices. We demonstrate theoretically that a bi-layer of a heavy metal (Pt) and a bi-axial antiferromagnetic (AFM) dielectric (NiO) can be a source of a coherent THz signal. A spin-current flowing from a DC-current-driven Pt layer and polarized along the hard AFM anisotropy axis excites a non-uniform in time precession of magnetizations sublattices in the AFM, due to the presence of a weak easy-plane AFM anisotropy. The frequency of the AFM oscillations varies in the range of 0.1–2.0 THz with the driving current in the Pt layer from 108 A/cm2 to 109 A/cm2. The THz-frequency signal from the AFM with the amplitude exceeding 1 V/cm is picked up by the inverse spin-Hall effect in Pt. The operation of a room-temperature AFM THz-frequency oscillator is similar to that of a cryogenic JJ oscillator, with the energy of the easy-plane magnetic anisotropy playing the role of the Josephson energy.

15. Laser Micromachining of THz Components

DTIC Science & Technology

2000-09-29

such an instrument [3] for use on the Large Binocular Telescope now being constructed on Mount Graham, Arizona. Before operation the cell is evacuated...micromachined, 2 THz array receiver being developed for SOFIA, the Stratospheric Observatory for Far Infrared •: Astronomy [3]. Test feedhorns for the array

16. Dispersion of carbon nanotubes in melt compounded polypropylene based composites investigated by THz spectroscopy.

PubMed

Casini, R; Papari, G; Andreone, A; Marrazzo, D; Patti, A; Russo, P

2015-07-13

We investigate the use of Terahertz (THz) Time Domain Spectroscopy (TDS) as a tool for the measurement of the index dispersion of multi-walled carbon nanotubes (MWCNT) in polypropylene (PP) based composites. Samples containing 0.5% by volume concentration of non-functionalized and functionalized carbon nanotubes are prepared by melt compounding technology. Results indicate that the THz response of the investigated nanocomposites is strongly dependent on the kind of nanotube functionalization, which in turn impacts on the level of dispersion inside the polymer matrix. We show that specific dielectric parameters such as the refractive index and the absorption coefficient measured by THz spectroscopy can be both correlated to the index of dispersion as estimated using conventional optical microscopy.

17. Optical and THz investigations of mid-IR materials exposed to alpha particle irradiation

NASA Astrophysics Data System (ADS)

Sporea, Dan; Mihai, Laura; Sporea, Adelina; Vâţã, Ion

2017-01-01

The paper is the first comprehensive study on alpha particle irradiation effects on four mid-IR materials: CaF2, BaF2, Al2O3 (sapphire) and ZnSe. The measurements of the optical spectral transmittance, spectral diffuse reflectance, radioluminescent emission, terahertz (THz) spectral response, transmittance, absorbance, refractive index, real and imaginary parts of the dielectric constant and THz imaging are used as complementary investigations to evaluate these effects. The simulations were run to estimate: (i) the penetration depth, (ii) the scattering of alpha particle beam, (iii) the amount of material affected by this interaction, and (iv) the number of vacancies produced by the radiation exposure for each type of material. The simulation results are compared to the off-line measurement outcomes. The delay and spectral composition change of the reflected THz signal highlight the modification induced in the tested materials by the irradiation process.

18. Optical and THz investigations of mid-IR materials exposed to alpha particle irradiation

PubMed Central

Sporea, Dan; Mihai, Laura; Sporea, Adelina; Vâţã, Ion

2017-01-01

The paper is the first comprehensive study on alpha particle irradiation effects on four mid-IR materials: CaF2, BaF2, Al2O3 (sapphire) and ZnSe. The measurements of the optical spectral transmittance, spectral diffuse reflectance, radioluminescent emission, terahertz (THz) spectral response, transmittance, absorbance, refractive index, real and imaginary parts of the dielectric constant and THz imaging are used as complementary investigations to evaluate these effects. The simulations were run to estimate: (i) the penetration depth, (ii) the scattering of alpha particle beam, (iii) the amount of material affected by this interaction, and (iv) the number of vacancies produced by the radiation exposure for each type of material. The simulation results are compared to the off-line measurement outcomes. The delay and spectral composition change of the reflected THz signal highlight the modification induced in the tested materials by the irradiation process. PMID:28067289

19. Long-range guided THz radiation by thin layers of water.

PubMed

Sczech, Robert; Rivas, Jaime Gómez; Berrier, Audrey; Giannini, Vincenzo; Pirruccio, Giuseppe; Debus, Christian; Schäfer-Eberwein, Heiko; Bolívar, Peter Haring

2012-12-03

We propose a novel method to guide THz radiation with low losses along thin layers of water. This approach is based on the coupling of evanescent surface fields at the opposite sides of the thin water layer surrounded by a dielectric material, which leads to a maximum field amplitude at the interfaces and a reduction of the energy density inside the water film. In spite of the strong absorption of water in this frequency range, calculations show that the field distribution can lead to propagation lengths of several centimeters. By means of attenuated total reflection measurements we demonstrate the coupling of incident THz radiation to the long-range surface guided modes across a layer of water with a thickness of 24 μm. This first demonstration paves the way for THz sensing in aqueous environments.

20. Evaluation of SiO2@CoFe2O4 nano-hollow spheres through THz pulses

NASA Astrophysics Data System (ADS)

Rakshit, Rupali; Pal, Monalisa; Serita, Kazunori; Chaudhuri, Arka; Tonouchi, Masayoshi; Mandal, Kalyan

2016-05-01

We have synthesized cobalt ferrite (CFO) nanoparticles (NPs) of diameter 100 nm and nano-hollow spheres (NHSs) of diameter 100, 160, 250, and 350 nm by a facile one step template free solvothermal technique and carried out SiO2 coating on their surface following Stöber method. The phase and morphology of the nanostructures were confirmed by X-ray diffraction and transmission electron microscope. The magnetic measurements were carried out by vibrating sample magnetometer in order to study the influence of SiO2 coating on the magnetic properties of bare CFO nanostructures. Furthermore, we have applied THz time domain spectroscopy to investigate the THz absorption property of these nanostructures in the frequency range 1.0-2.5 THz. Detailed morphology and size dependent THz absorption study unfolds that the absorption property of these nanostructures sensitively carries the unique signature of its dielectric property.

1. Improvement of passive THz camera images

NASA Astrophysics Data System (ADS)

Kowalski, Marcin; Piszczek, Marek; Palka, Norbert; Szustakowski, Mieczyslaw

2012-10-01

Terahertz technology is one of emerging technologies that has a potential to change our life. There are a lot of attractive applications in fields like security, astronomy, biology and medicine. Until recent years, terahertz (THz) waves were an undiscovered, or most importantly, an unexploited area of electromagnetic spectrum. The reasons of this fact were difficulties in generation and detection of THz waves. Recent advances in hardware technology have started to open up the field to new applications such as THz imaging. The THz waves can penetrate through various materials. However, automated processing of THz images can be challenging. The THz frequency band is specially suited for clothes penetration because this radiation does not point any harmful ionizing effects thus it is safe for human beings. Strong technology development in this band have sparked with few interesting devices. Even if the development of THz cameras is an emerging topic, commercially available passive cameras still offer images of poor quality mainly because of its low resolution and low detectors sensitivity. Therefore, THz image processing is very challenging and urgent topic. Digital THz image processing is a really promising and cost-effective way for demanding security and defense applications. In the article we demonstrate the results of image quality enhancement and image fusion of images captured by a commercially available passive THz camera by means of various combined methods. Our research is focused on dangerous objects detection - guns, knives and bombs hidden under some popular types of clothing.

2. A compact THz imaging system

NASA Astrophysics Data System (ADS)

Sešek, Aleksander; Å vigelj, Andrej; Trontelj, Janez

2015-03-01

The objective of this paper is the development of a compact low cost imaging THz system, usable for observation of the objects near to the system and also for stand-off detection. The performance of the system remains at the high standard of more expensive and bulkiest system on the market. It is easy to operate as it is not dependent on any fine mechanical adjustments. As it is compact and it consumes low power, also a portable system was developed for stand-off detection of concealed objects under textile or inside packages. These requirements rule out all optical systems like Time Domain Spectroscopy systems which need fine optical component positioning and requires a large amount of time to perform a scan and the image capture pixel-by-pixel. They are also almost not suitable for stand-off detection due to low output power. In the paper the antenna - bolometer sensor microstructure is presented and the THz system described. Analysis and design guidelines for the bolometer itself are discussed. The measurement results for both near and stand-off THz imaging are also presented.

3. Frequency dependent optical and dielectric properties of zinc sulfide in Terahertz regime

NASA Astrophysics Data System (ADS)

Ganti, Satya R.; Sundaram, S. K.; McCloy, John S.

2014-07-01

Frequency dependent optical and dielectric properties for several grades of chemical vapor deposited (CVD) zinc sulfide (standard, elemental, and multi-spectral) was performed using a terahertz time-domain spectroscopy (THz-TDS) system in the frequency range from 0.15 THz to 2.5 THz. Zinc sulfide exhibits low frequency vibrational modes characterized by the THz-TDS. Two low-frequency phonon resonance lines were revealed at 0.78 THz and 2.20 THz. These samples were also characterized in the GHz range using a backward wave oscillator (BWO) source quasi-optical spectrometer, and the data obtained by both approaches were compared. Experimental data were also compared with an undamped harmonic oscillator model. These results compare well with the literature values obtained using other methods.

4. Enhancing the low frequency THz resonances (< 1 THz) of organic molecules via electronegative atom substitution

NASA Astrophysics Data System (ADS)

Dash, Jyotirmayee; Ray, Shaumik; Pesala, Bala

2015-03-01

Terahertz (THz) technology is an active area of research with various applications in non-intrusive imaging and spectroscopy. Very few organic molecules have significant resonances below 1 THz. Understanding the origin of low frequency THz modes in these molecules and their absence in other molecules could be extremely important in design and engineering molecules with low frequency THz resonances. These engineered molecules can be used as THz tags for anti-counterfeiting applications. Studies show that low frequency THz resonances are commonly observed in molecules having higher molecular mass and weak intermolecular hydrogen bonds. In this paper, we have explored the possibility of enhancing the strength of THz resonances below 1 THz through electronegative atom substitution. Adding an electronegative atom helps in achieving higher hydrogen bond strength to enhance the resonances below 1 THz. Here acetanilide has been used as a model system. THz-Time Domain Spectroscopy (THz-TDS) results show that acetanilide has a small peak observed below 1 THz. Acetanilide can be converted to 2-fluoroacetanilide by adding an electronegative atom, fluorine, which doesn't have any prominent peak below 1 THz. However, by optimally choosing the position of the electronegative atom as in 4-fluoroacetanilide, a significant THz resonance at 0.86 THz is observed. The origin of low frequency resonances can be understood by carrying out Density Functional Theory (DFT) simulations of full crystal structure. These studies show that adding an electronegative atom to the organic molecules at an optimized position can result in significantly enhanced resonances below 1 THz.

5. Non-invasive Florentine Renaissance Panel Painting Replica Structures Investigation by Using Terahertz Time-Domain Imaging (THz-TDI) Technique

NASA Astrophysics Data System (ADS)

Koch Dandolo, Corinna L.; Picollo, Marcello; Cucci, Costanza; Jepsen, Peter Uhd

2016-11-01

The potentials of the Terahertz Time-Domain Imaging (THz-TDI) technique for a non-invasive inspection of panel paintings have been considered in detail. The THz-TD data acquired on a replica of a panel painting made in imitation of Italian Renaissance panel paintings were processed in order to provide insights as to the limits and potentials of the technique in detecting different kinds of underdrawings and paint layers. Constituent layers, construction techniques, and anomalies were identified and localized by interpreting the extracted THz dielectric stratigraphy.

6. Study on the THz spectrum of methamphetamine

NASA Astrophysics Data System (ADS)

Ning, Li; Shen, Jingling; Jinhai, Sun; Laishun, Liang; Xu, Xiaoyu; Lu, Meihong; Yan, Jia

2005-09-01

The spectral absorption features of methamphetamine (MA), one of the most widely consumed illicit drugs in the world, are studied experimentally by Terahertz (THz) time-domain spectroscopy (THz-TDS), and the characteristic absorption spectra are obtained in the range of 0.2 to 2.6 THz. The vibrational frequencies are calculated using the density functional theory (DFT). Theoretical results show significant agreement with experimental results, and identification of vibrational modes are given. The calculated results further confirm that the characteristic frequencies come from the collective vibrational modes. The results suggest that use of the THz-TDS technique can be an effective way to inspect for illicit drugs.

7. Fabrication of THz Sensor with Metamaterial Absorber

NASA Astrophysics Data System (ADS)

Gonzalez, Hugo; Alves, Fabio; Karunasiri, Gamani

The terahertz (THz) portion of the electromagnetic spectrum (0.1-10 THz) has not been fully utilized due to the lack of sensitive detectors. Real-time imaging in this spectral range has been demonstrated using uncooled infrared microbolometer cameras and external illumination provided by quantum cascade laser (QCL) based THz sources. However, the microbolometer pixels in the cameras have not been optimized to achieve high sensitivity in THz frequencies. Recently, we have developed a highly sensitive micromechanical THz sensor employing bi-material effect with an integrated metamaterial absorber tuned to the THz frequency of interest. The use of bi-material structures causes deflection on the sensor to as the absorbed THz radiation increases its temperature, which can be monitored optically by reflecting a light beam. This approach eliminates the integration of readout electronics needed in microbolometers. The absorption of THz by metamaterial can be tailored by controlling geometrical parameters. The sensors can be fabricated using conventional microelectronic materials and incorporated into pixels to form focal plane arrays (FPAs). In this presentation, characterization and readout of a THz sensor with integrated metamaterial structure will be described. Supported by DoD.

8. Terahertz (THz) Wireless Systems for Space Applications

NASA Technical Reports Server (NTRS)

Hwu, Shian U.; deSilva, Kanishka B.; Jih, Cindy T.

2013-01-01

NASA has been leading the Terahertz (THz) technology development for the sensors and instruments in astronomy in the past 20 years. THz technologies are expanding into much broader applications in recent years. Due to the vast available multiple gigahertz (GHz) broad bandwidths, THz radios offer the possibility for wireless transmission of high data rates. Multi-Gigabits per second (MGbps) broadband wireless access based on THz waves are closer to reality. The THz signal high atmosphere attenuation could significantly decrease the communication ranges and transmittable data rates for the ground systems. Contrary to the THz applications on the ground, the space applications in the atmosphere free environment do not suffer the atmosphere attenuation. The manufacturing technologies for the THz electronic components are advancing and maturing. There is great potential for the NASA future high data wireless applications in environments with difficult cabling and size/weight constraints. In this study, the THz wireless systems for potential space applications were investigated. The applicability of THz systems for space applications was analyzed. The link analysis indicates that MGbps data rates are achievable with compact sized high gain antennas.

9. Curvature Control of Silicon Microlens for THz Dielectric Antenna

NASA Technical Reports Server (NTRS)

Lee, Choonsup; Chattopadhyay, Goutam; Cooper, Ken; Mehdi, Imran

2012-01-01

We have controlled the curvature of silicon microlens by changing the amount of photoresist in order to microfabricate hemispherical silicon microlens which can improve the directivity and reduce substrate mode losses.

10. Dielectric Properties of Diesel and Gasoline by Terahertz Spectroscopy

NASA Astrophysics Data System (ADS)

Arik, Enis; Altan, Hakan; Esenturk, Okan

2014-09-01

In this study we have investigated the dielectric properties of diesel and gasoline in the Terahertz (THz) spectral region. We present frequency dependent absorption coefficients, refractive indices, and dielectric constants calculated from the transient measurements of the fuel oils between 0.1 and 1.1 THz. Observed weak absorption coefficient of fuel oils is explained by transient dipole moments induced by collisions between individual molecules. Fuel oils were modeled successfully with Debye model to investigate the relaxation dynamics after interaction with the electric field. Significant differences in relaxation times of molecules in diesel and gasoline are attributed to the differences in their intermolecular forces. Dispersion forces are much greater in diesel due to the longer hydrocarbon chains (C8-C40) compared to that (C4-C12) of the gasoline. This leads to a comparably faster relaxation right after THz electric field is applied. Clear differences in optical properties offer a simple yet effective way to discriminate fuel oils from each other by using THz spectroscopy without any danger of combustion or decomposition of the samples. Such an approach may also be used for the quality determination of either fuels. The study presents the great potential of THz spectroscopy to study very complex mixtures like fuel oils by the use of instantaneous THz wave/matter interactions and relaxation dynamics of the constituent molecules.

11. Tactical systems applications for THz devices

SciTech Connect

McGee, R.A.

1994-12-31

Currently several weapons systems use millimeter wave, infrared or both for sensing. THz technology is spectrally located so as to be able to exploit the best features of MMW and infrared technology. The items for discussion are Army needs that could be addressed by THz technology. The emphasis is on active and passive sensing parameters for Smart munitions and combat vehicles.

12. High power THz sources for nonlinear imaging

SciTech Connect

Tekavec, Patrick F.; Kozlov, Vladimir G.

2014-02-18

Many biological and chemical compounds have unique absorption features in the THz (0.1 - 10 THz) region, making the use of THz waves attractive for imaging in defense, security, biomedical imaging, and monitoring of industrial processes. Unlike optical radiation, THz frequencies can pass through many substances such as paper, clothing, ceramic, etc. with little attenuation. The use of currently available THz systems is limited by lack of highpower, sources as well as sensitive detectors and detector arrays operating at room temperature. Here we present a novel, high power THz source based on intracavity downconverison of optical pulses. The source delivers 6 ps pulses at 1.5 THz, with an average power of >300 μW and peak powers >450 mW. We propose an imaging method based on frequency upconverison that is ideally suited to use the narrow bandwidth and high peak powers produced by the source. By upconverting the THz image to the infrared, commercially available detectors can be used for real time imaging.

13. THz imaging of histo-pathological samples

NASA Astrophysics Data System (ADS)

Knobloch, Pascal; Schmalstieg, K.; Koch, Martin; Rehberg, E.; Vauti, F.; Donhuijsen, K.

2001-10-01

We investigate the potential of THz imaging for the examination of histo-pathological samples. Data obtained on a pig larynx and on a human liver containing cancerous tissue are presented. Different types of tissue are clearly resolved due to their distinct spectral absorption characteristics or due to a density dependent THz transmission.

14. Laser Micromachining Fabrication of THz Components

NASA Technical Reports Server (NTRS)

DrouetdAubigny, C.; Walker, C.; Jones, B.; Groppi, C.; Papapolymerou, J.; Tavenier, C.

2001-01-01

Laser micromachining techniques can be used to fabricate high-quality waveguide structures and quasi-optical components to micrometer accuracies. Successful GHz designs can be directly scaled to THz frequencies. We expect this promising technology to allow the construction of the first fully integrated THz heterodyne imaging arrays. At the University of Arizona, construction of the first laser micromachining system designed for THz waveguide components fabrication has been completed. Once tested and characterized our system will be used to construct prototype THz lx4 focal plane mixer arrays, magic tees, AR coated silicon lenses, local oscillator source phase gratings, filters and more. Our system can micro-machine structures down to a few microns accuracy and up to 6 inches across in a short time. This paper discusses the design and performance of our micromachining system, and illustrates the type, range and performance of components this exciting new technology will make accessible to the THz community.

15. Majolica imaging with THz waves: preliminary results

NASA Astrophysics Data System (ADS)

Catapano, Ilaria; Affinito, Antonio; Guerriero, Luigi; Bisceglia, Bruno; Soldovieri, Francesco

2016-05-01

Recent advancements performed in the development of stable and flexible devices working at TeraHertz (THz) frequencies have opened the way at considering this technology as a very interesting noninvasive diagnostic tool in cultural heritage. In this frame, the paper aims at assessing the ability of THz imaging to gather information about preservation state and constructive modalities of majolica artworks. In particular, THz surveys have been carried out on two majolica tiles dated back to the nineteenth century and realized as building cladding at Naples (Italy). The analysis has been performed by means of the Zomega fiber-coupled THz time-domain system. This analysis corroborates the ability of THz to reconstruct irregularities of majolica tile topography, to characterize pigment and glaze losses, and to detect and localize glaze and pigment layer as well as the glaze-clay body interface.

16. Surface sealing using self-assembled monolayers and its effect on metal diffusion in porous low-k dielectrics studied using monoenergetic positron beams

NASA Astrophysics Data System (ADS)

Uedono, Akira; Armini, Silvia; Zhang, Yu; Kakizaki, Takeaki; Krause-Rehberg, Reinhard; Anwand, Wolfgang; Wagner, Andreas

2016-04-01

Surface sealing effects on the diffusion of metal atoms in porous organosilicate glass (OSG) films were studied by monoenergetic positron beams. For a Cu(5 nm)/MnN(3 nm)/OSG(130 nm) sample fabricated with pore stuffing, C4F8 plasma etch, unstuffing, and a self-assembled monolayer (SAM) sealing process, it was found that pores with cubic pore side lengths of 1.1 and 3.1 nm coexisted in the OSG film. For the sample without the SAM sealing process, metal (Cu and Mn) atoms diffused from the top Cu/MnN layer into the OSG film and were trapped by the pores. As a result, almost all pore interiors were covered with those metals. For the sample damaged by an Ar/C4F8 plasma etch treatment before the SAM sealing process, SAMs diffused into the OSG film, and they were preferentially trapped by larger pores. The cubic pore side length in these pores containing self-assembled molecules was estimated to be 0.7 nm. Through this work, we have demonstrated that monoenergetic positron beams are a powerful tool for characterizing capped porous films and the trapping of atoms and molecules by pores.

17. ASK modulator based on switchable FSS for THz applications

NASA Astrophysics Data System (ADS)

Kiani, Ghaffer I.; Bird, Trevor S.

2011-04-01

An amplitude shift keying modulator that is based on a switchable frequency selective surface (FSS) is described for THz communication. The FSS uses a square loop aperture geometry, with each unit cell having four PIN diodes across the aperture at 90 degree intervals. To minimize the effect of bias lines on the overall frequency response of the FSS, a crossed-shape negative dc bias line, which is connected to the center of the FSS unit cell, has been placed on the rear surface of the dielectric substrate. Positive dc biasing is provided from the front side of the FSS structure. Simulation results are presented for two possible operating frequencies and two principal polarizations at normal and oblique incidence. These show that a free space modulator based on the proposed FSS structure would provide about 19 dB transmission loss at 600 GHz between on and off states of the PIN diodes for both transverse electric and transverse magnetic polarizations.

18. Slot-line end-fire antennas for THz frequencies

NASA Technical Reports Server (NTRS)

Ekstroem, H.; Gearhart, S.; Acharya, P. R.; Dave, H.; Rebeiz, G.; Jacobsson, S.; Kollberg, E.; Chin, G.

1992-01-01

Tapered slot-line endfire antennas, of BLTSA type, have been fabricated on 1.7 micron thin SiO2/Si3N4 (epsilon (sub r) = 4.5) dielectric membranes. The antenna patterns, in the E-, H-, D- and D-cross planes, were measured at 270, 348, 370, and 802 GHz using bismuth micro bolometer detectors. The antennas have approximately 12 dB directivity, and the -10 dB beam widths are 50 and 55 degrees in the E- and H-planes at 348 GHz, respectively. The measurements at millimeter/submillimeter wavelengths compare well with scale measurements at 45 GHz as well as with theoretical predictions. The overall results are encouraging and show that slot-line antennas can be fabricated for use at THz frequencies. Furthermore, it is shown that the very thin SiO2/Si3N4 membranes are strong enough to be used in practical applications.

19. The Thz Spectrum of Glycolaldehyde

NASA Astrophysics Data System (ADS)

Goubet, Manuel; Huet, Therese R.; Haykal, Imane; Margules, Laurent; Pirali, Olivier; Roy, Pascale

2011-06-01

The vibration-rotation spectrum of the ν_1-0, ν_2-0 and ν_3-0 bands of glycolaldehyde was recorded up to 12 THz, using the far-infrared beamline AILES at the synchrotron SOLEIL and a Fourier transform spectrometer coupled to a multipass cell. More than eight thousands lines were assigned, revealing the rotation structure up to J=80, K_a=38 for the ground state. The THz data were fitted simultaneously with pure rotational transitions of better accuracy observed in the microwave (1), in the millimeter-wave (2) and in the sub-millimeter-wave (3) range. In addition new data were recorded at Lille in the 150-300 GHz and 750-950 GHz range. The THz lines and the microwave - (sub)-millimeterwave lines are reproduced with a standard deviation of 2 10-4 Cm-1 and 40 KHz, respectively. Glycolaldehyde has been identified toward the galactic center (4). The vibrational state partition function can be re-evaluated according to the bands origins associated with ν_1, ν_2, and ν_3, which are observed experimentally for the first time. This work is supported by the Programme National de Physico-Chimie du Milieu Interstellaire (PCMI-CNRS) and by the contract ANR-08-BLAN-0054. 1. M. Rey, J.-R. Aviles-Moreno and T. R. Huet, Chem. Phys. Lett. 430(2006) 121 ; K.-M. Marstokk and H. Mollendal, J. Mol. Struct. 5 (1970) 205. 2. R. A. H. Butler, F. C. De Lucia, D. T. Petkie, H. Mollendal, A. Horn, and E. Herbst, ApJS 134 (2001) 319. ; S. L. Widicus-Weaver, R. A. H. Butler, B. J. Drouin, D. T. Petkie, K. A. Dyl, F. C. De Lucia, and G. A. Blake, ApJ 158(2005)188. 3. P. B. Carroll, B. J. Drouin, and S. L. Widicus-Weaver, ApJ 723 (2010) 845. 4. J. M. Hollis, S. N. Vogel, L. E. Snyder, P. R. Jewell, and F. J. Lovas, ApJ 554 (2001) L81. ; M.T. Beltran, C. Codella, S. Viti, R. Niri, R. Cesaroni, ApJ 690 (2009) L93.

20. THz dynamics of nanoconfined water by ultrafast optical spectroscopy

NASA Astrophysics Data System (ADS)

Taschin, A.; Bartolini, P.; Torre, R.

2017-01-01

We investigated the vibrational dynamics and structural relaxation of water nanoconfined in porous silica samples with a pore size of 4 nm at different levels of hydration and temperature. We used the time-resolved optical Kerr effect (OKE), a spectroscopic technique that enables investigation of ultrafast water dynamics in a wide time (0.1-10 ps) or frequency (10-0.1 THz) window. At low hydration levels corresponding to two complete superficial water layers, no freezing occurs and the water remains mobile at all investigated temperatures. Meanwhile, at full hydration we witness a partial ice formation at about 248 K that coexists with the surface water remaining in the supercooled state. At low hydration, both structural and vibrational dynamics show significant modifications compared to bulk liquid water. This is due to the strong interaction of the water molecules with silica surfaces. Inner water, however, reveals relaxation dynamics very similar to bulk water.

1. Measurement of complex terahertz dielectric properties of polymers using an improved free-space technique

NASA Astrophysics Data System (ADS)

Chang, Tianying; Zhang, Xiansheng; Yang, Chuanfa; Sun, Zhonglin; Cui, Hong-Liang

2017-04-01

The complex dielectric properties of non-polar solid polymer materials were measured in the terahertz (THz) band by a free-space technique employing a frequency-extended vector network analyzer (VNA), and by THz time-domain spectroscopy (TDS). Mindful of THz wave’s unique characteristics, the free-space method for measurement of material dielectric properties in the microwave band was expanded and improved for application in the THz frequency region. To ascertain the soundness and utility of the proposed method, measurements of the complex dielectric properties of a variety of polymers were carried out, including polytetrafluoroethylene (PTFE, known also by the brand name Teflon), polypropylene (PP), polyethylene (PE), and glass fiber resin (Composite Stone). The free-space method relies on the determination of electromagnetic scattering parameters (S-parameters) of the sample, with the gated-reflect-line (GRL) calibration technique commonly employed using a VNA. Subsequently, based on the S-parameters, the dielectric constant and loss characteristic of the sample were calculated by using a Newtonian iterative algorithm. To verify the calculated results, THz TDS technique, which produced Fresnel parameters such as reflection and transmission coefficients, was also used to independently determine the dielectric properties of these polymer samples, with results satisfactorily corroborating those obtained by the free-space extended microwave technique.

2. THz spectroscopy of D2H+

NASA Astrophysics Data System (ADS)

Yu, S.; Pearson, J. C.; Amano, T.; Matsushima, F.

2017-01-01

We extended the measurements of the rotational transitions of D2H+ up to 3 THz by using the JPL frequency multiplier chains and a TuFIR system at Toyama. D2H+ was generated in an extended negative glow discharge cell cooled to liquid nitrogen temperature. We observed five new THz lines. All the available rotational transition frequencies together with the combination differences derived from the three fundamental bands were subject to least square analysis to determine the molecular constants. New THz measurements are definitely useful for better characterization of spectroscopic properties. The improved molecular constants provide better predictions of other unobserved rotational transitions.

3. DNA detection by THz pumping

SciTech Connect

Chernev, A. L.; Bagraev, N. T.; Klyachkin, L. E.; Emelyanov, A. K.; Dubina, M. V.

2015-07-15

DNA semiconductor detection and sequencing is considered to be the most promising approach for future discoveries in genome and proteome research which is dramatically dependent on the challenges faced by semiconductor nanotechnologies. DNA pH-sensing with ion-sensitive field effect transistor (ISFET) is well-known to be a successfully applied electronic platform for genetic research. However this method lacks fundamentally in chemical specificity. Here we develop the first ever silicon nanosandwich pump device, which provides both the excitation of DNA fragments’ self-resonant modes and the feedback for current-voltage measurements at room temperature. This device allows direct detection of singlestranded label-free oligonucleotides by measuring their THz frequency response in aqueous solution. These results provide a new insight into the nanobioelectronics for the future real-time technologies of direct gene observations.

4. Experimental realization of a terahertz all-dielectric metasurface absorber.

PubMed

Liu, Xinyu; Fan, Kebin; Shadrivov, Ilya V; Padilla, Willie J

2017-01-09

Metamaterial absorbers consisting of metal, metal-dielectric, or dielectric materials have been realized across much of the electromagnetic spectrum and have demonstrated novel properties and applications. However, most absorbers utilize metals and thus are limited in applicability due to their low melting point, high Ohmic loss and high thermal conductivity. Other approaches rely on large dielectric structures and / or a supporting dielectric substrate as a loss mechanism, thereby realizing large absorption volumes. Here we present a terahertz (THz) all dielectric metasurface absorber based on hybrid dielectric waveguide resonances. We tune the metasurface geometry in order to overlap electric and magnetic dipole resonances at the same frequency, thus achieving an experimental absorption of 97.5%. A simulated dielectric metasurface achieves a total absorption coefficient enhancement factor of FT=140, with a small absorption volume. Our experimental results are well described by theory and simulations and not limited to the THz range, but may be extended to microwave, infrared and optical frequencies. The concept of an all-dielectric metasurface absorber offers a new route for control of the emission and absorption of electromagnetic radiation from surfaces with potential applications in energy harvesting, imaging, and sensing.

5. s-SNOM based IR and THz spectroscopy for nanoscale material characterization

NASA Astrophysics Data System (ADS)

Gokus, Tobias; Huber, Andreas; Cernescu, Adrian

Scattering-type Scanning Near-field Optical Microscopy (s-SNOM) allows to overcome the diffraction limit of conventional light microscopy enabling optical measurements at a spatial resolution of 10nm. s-SNOM employs an externally-illuminated sharp metallic AFM tip to create a nanoscale hot-spot at its apex. The optical tip-sample near-field interaction is determined by the local dielectric properties (refractive index) of the sample and detection of the elastically tip-scattered light yields nanoscale resolved near-field images simultaneous to topography. Development of a dedicated Fourier-transform detection module for analyzing light scattered from the tip which is illuminated by a broadband laser source enables IR spectroscopy of complex polymer nanostructures. Applications presented further demonstrate characterization of embedded structural phases in biominerals (bone), organic semiconductors or functional semiconductor nanostructures.Furthermore, by extending the concept of broadband-s-SNOM spectroscopy to the THz-spectral range, we demonstrate optical near-field imaging and spectroscopy at THz-frequencies (0.5-2.5 THz) by coupling the free space beam of a dedicated THz-TDS to the s-SNOM system.

6. Development of THz wave oscillation and its application to molecular sciences

NASA Astrophysics Data System (ADS)

Nishizawa, J.

In 1967, a THz wave was generated for the first time using a free electron laser; however, the device was too expensive to be used widely. The author published the idea of THz wave generation by use of resonating vibration between paired atoms in polymer or crystal in 1965, and succeeded with K. Suto to generate a 12 THz wave in 1983. In 1999, the author invited K. Kawase and H. Ito to Sendai RIKEN to realize the concept by use of dielectrics; in 2000, they succeeded in realizing a sweep generator. In the same year, the author suggested the idea of applying the THz wave to cancer diagnosis and treatment, particularly by improving heating selectivity: This enhances the effect of medications by raising only the temperature of the cancer itself, not of the surrounding atomic pairs in the neighborhood. These applications are expected to spread quickly as powerful methodology based on molecular science. The reason for this is that the much improved waveform generated enables higher selectivity, allowing the detection of the existence of abnormal polymer near the paired atoms by measuring resonating frequency between paired atoms.

7. Morphological study of human sweat ducts for the investigation of THz-wave interaction (Conference Presentation)

NASA Astrophysics Data System (ADS)

Kawase, Kodo; Tripathi, Saroj R.

2016-03-01

Recently, some studies reported that the sweat ducts act as a low-Q-factor helical antenna due to their helical structure, and resonate in the terahertz frequency range according to their structural parameters. According to the antenna theory, when the duct works as a helical antenna, the dimension of the helix plays a key role to determine the frequency of resonance. Therefore, the accurate determination of structural parameters of sweat duct is crucially important to obtain the reliable frequency of resonance and modes of operations. Therefore, here we performed the optical coherence tomography (OCT) of human subjects on their palm and foot to investigate the density, distribution and morphological features of sweat ducts. Moreover, we measured the dielectric properties of stratum corneum using terahertz time domain spectroscopy and based upon this information, we determined the frequency of resonance. We recruited 32 subjects for the measurement and the average duct diameter was 95±11μm. Based upon this information on diameter of duct and THz dielectric properties of stratum corneum (ɛ=5.1±1.3), we have calculated the frequency of resonance of sweat duct. Finally, we determined that the center frequency of resonance was 442±76 GHz. We believe that these findings will facilitate further investigation of the THz-skin interaction and provide guidelines for safety levels with respect to human exposure. We will also report on the EEG measurement while being shined by micro watt order THz waves.

8. Enhancement of optics-to-THz conversion efficiency by metallic slot waveguides.

PubMed

Ruan, Zhichao; Veronis, Georgios; Vodopyanov, Konstantin L; Fejer, Marty M; Fan, Shanhui

2009-08-03

A metallic slot waveguide, with a dielectric strip embedded within, is investigated for the purpose of enhancing the optics-to-THz conversion efficiency using the difference-frequency generation (DFG) process. To describe the frequency conversion process in such lossy waveguides, a fully-vectorial coupled-mode theory is developed. Using the coupled-mode theory, we outline the basic theoretical requirements for efficient frequency conversion, which include the needs to achieve large coupling coefficients, phase matching, and low propagation loss for both the optical and THz waves. Following these requirements, a metallic waveguide is designed by considering the trade-off between modal confinement and propagation loss. Our numerical calculation shows that the conversion efficiency in these waveguide structures can be more than one order of magnitude larger than what has been achieved using dielectric waveguides. Based on the distinct impact of the slot width on the optical and THz modal dispersion, we propose a two-step method to realize the phase matching for general pump wavelengths.

9. THz Medical Imaging: in vivo Hydration Sensing

PubMed Central

Taylor, Zachary D.; Singh, Rahul S.; Bennett, David B.; Tewari, Priyamvada; Kealey, Colin P.; Bajwa, Neha; Culjat, Martin O.; Stojadinovic, Alexander; Lee, Hua; Hubschman, Jean-Pierre; Brown, Elliott R.; Grundfest, Warren S.

2015-01-01

The application of THz to medical imaging is experiencing a surge in both interest and federal funding. A brief overview of the field is provided along with promising and emerging applications and ongoing research. THz imaging phenomenology is discussed and tradeoffs are identified. A THz medical imaging system, operating at ~525 GHz center frequency with ~125 GHz of response normalized bandwidth is introduced and details regarding principles of operation are provided. Two promising medical applications of THz imaging are presented: skin burns and cornea. For burns, images of second degree, partial thickness burns were obtained in rat models in vivo over an 8 hour period. These images clearly show the formation and progression of edema in and around the burn wound area. For cornea, experimental data measuring the hydration of ex vivo porcine cornea under drying is presented demonstrating utility in ophthalmologic applications. PMID:26085958

10. THz Detection and Imaging using Rydberg Atoms

NASA Astrophysics Data System (ADS)

Wade, Christopher; Sibalic, Nikola; Kondo, Jorge; de Melo, Natalia; Adams, Charles; Weatherill, Kevin

2016-05-01

Atoms make excellent electromagnetic field sensors because each atom of the same isotope is identical and has well-studied, permanent properties allowing calibration to SI units. Thus far, atoms have not generally been exploited for terahertz detection because transitions from the atomic ground state are constrained to a limited selection of microwave and optical frequencies. In contrast, highly excited Rydberg' states allow us access to many strong, electric dipole transitions from the RF to THz regimes. Recent advances in the coherent optical detection of Rydberg atoms have been exploited by a number of groups for precision microwave electrometry Here we report the demonstration of a room-temperature, cesium Rydberg gas as a THz to optical interface. We present two configurations: First, THz-induced fluorescence offers non-destructive and direct imaging of the THz field, providing real-time, single shot images. Second, we convert narrowband terahertz photons to infrared photons with 6% quantum efficiency allowing us to use nano-Watts of THz power to control micro-Watts of laser power on microsecond timescales. Exploiting hysteresis and a room-temperature phase transition in the response of the medium, we demonstrate a latching optical memory for sub pico-Joule THz pulses.

11. Study of Application of Thz Time Domainspectroscopy in Food Safet

NASA Astrophysics Data System (ADS)

Lang, Liying; Cai, Na

In this paper, a new spectroscopy technology named terahertz time-domain spectroscopy (THz-TDS) is introduced, which is used in food safety. We describe a coherent subpicosecond THz spectroscopy system based on nonresonant optical rectification for the generation of THz radiation. As an example, we measured absorption spectrum of water vapor by THz-TDS in frequency from 0.5 to 2.5 THz, The experiment demonstrated that the spectroscopy resolution of system was up to 0.0001THz, which can be measured vegetable pesticide residual, for it neither need sample pretreatment nor cause pollution.

12. Analysis of band structure, transmission properties, and dispersion behavior of THz wave in one-dimensional parabolic plasma photonic crystal

SciTech Connect

Askari, Nasim; Eslami, Esmaeil; Mirzaie, Reza

2015-11-15

The photonic band gap of obliquely incident terahertz electromagnetic waves in a one-dimensional plasma photonic crystal is studied. The periodic structure consists of lossless dielectric and inhomogeneous plasma with a parabolic density profile. The dispersion relation and the THz wave transmittance are analyzed based on the electromagnetic equations and transfer matrix method. The dependence of effective plasma frequency and photonic band gap characteristics on dielectric and plasma thickness, plasma density, and incident angle are discussed in detail. A theoretical calculation for effective plasma frequency is presented and compared with numerical results. Results of these two methods are in good agreement.

13. Novel detectors for traceable THz power measurements

NASA Astrophysics Data System (ADS)

Müller, Ralf; Bohmeyer, Werner; Kehrt, Mathias; Lange, Karsten; Monte, Christian; Steiger, Andreas

2014-08-01

Several novel types of detectors for the measurement of electromagnetic radiation in the THz spectral range are described. Firstly, detectors based on pyroelectric foil coated with different absorbers have been developed focusing on the following features: high accuracy due to well-characterized absorption, high sensitivity, large area absorbers and frequency and polarization independence. A three-dimensional design with five absorptions gave an overall absorption of more than 98 %. Secondly, detectors based on pyroelectric foils with thin metal layers were realized. An absorption of 50 % can be obtained if the thickness of the layers is carefully adjusted. According to electromagnetic theory this degree of absorption is independent of the polarization and frequency of the radiation in a wide range from at least 20 GHz to 5 THz. The third type of detector is based on a new type of volume absorber with a polished front surface and a gold-coated back side. It is the absorber of choice of the standard power detector for disseminating the spectral power responsivity scale. This standard detector allows the application of a physical model to calculate its spectral responsivity in the range from 1 THz to 5 THz if the detector has been calibrated at one single frequency. Finally, a THz detector calibration facility was set up and is now in operation at PTB to calibrate detectors from customers with an uncertainty as low as 1.7 %.

14. Method of casting patterned dielectric structures

DOEpatents

Poco, John F.; Hrubesh, Lawrence W.

2001-01-01

A pattern of dielectric structures are formed directly on a substrate in a single step using sol-gel chemistry and molding procedures. The resulting dielectric structures are useful in vacuum applications for electronic devices. Porous, lightweight structures having a high aspect ratio that are suitable for use as spacers between the faceplate and baseplate of a field emission display can be manufactured using this method.

15. Tunable Room Temperature THz Sources Based on Nonlinear Mixing in a Hybrid Optical and THz Micro-Ring Resonator

NASA Astrophysics Data System (ADS)

Sinha, Raju; Karabiyik, Mustafa; Al-Amin, Chowdhury; Vabbina, Phani K.; Güney, Durdu Ö.; Pala, Nezih

2015-03-01

We propose and systematically investigate a novel tunable, compact room temperature terahertz (THz) source based on difference frequency generation in a hybrid optical and THz micro-ring resonator. We describe detailed design steps of the source capable of generating THz wave in 0.5-10 THz with a tunability resolution of 0.05 THz by using high second order optical susceptibility (χ(2)) in crystals and polymers. In order to enhance THz generation compared to bulk nonlinear material, we employ a nonlinear optical micro-ring resonator with high-Q resonant modes for infrared input waves. Another ring oscillator with the same outer radius underneath the nonlinear ring with an insulation of SiO2 layer supports the generated THz with resonant modes and out-couples them into a THz waveguide. The phase matching condition is satisfied by engineering both the optical and THz resonators with appropriate effective indices. We analytically estimate THz output power of the device by using practical values of susceptibility in available crystals and polymers. The proposed source can enable tunable, compact THz emitters, on-chip integrated spectrometers, inspire a broader use of THz sources and motivate many important potential THz applications in different fields.

16. Tunable Room Temperature THz Sources Based on Nonlinear Mixing in a Hybrid Optical and THz Micro-Ring Resonator

PubMed Central

Sinha, Raju; Karabiyik, Mustafa; Al-Amin, Chowdhury; Vabbina, Phani K.; Güney, Durdu Ö.; Pala, Nezih

2015-01-01

We propose and systematically investigate a novel tunable, compact room temperature terahertz (THz) source based on difference frequency generation in a hybrid optical and THz micro-ring resonator. We describe detailed design steps of the source capable of generating THz wave in 0.5–10 THz with a tunability resolution of 0.05 THz by using high second order optical susceptibility (χ(2)) in crystals and polymers. In order to enhance THz generation compared to bulk nonlinear material, we employ a nonlinear optical micro-ring resonator with high-Q resonant modes for infrared input waves. Another ring oscillator with the same outer radius underneath the nonlinear ring with an insulation of SiO2 layer supports the generated THz with resonant modes and out-couples them into a THz waveguide. The phase matching condition is satisfied by engineering both the optical and THz resonators with appropriate effective indices. We analytically estimate THz output power of the device by using practical values of susceptibility in available crystals and polymers. The proposed source can enable tunable, compact THz emitters, on-chip integrated spectrometers, inspire a broader use of THz sources and motivate many important potential THz applications in different fields. PMID:25800287

17. RT-CW: widely tunable semiconductor THz QCL sources

NASA Astrophysics Data System (ADS)

Razeghi, M.; Lu, Q. Y.

2016-09-01

Distinctive position of Terahertz (THz) frequencies (ν 0.3 -10 THz) in the electromagnetic spectrum with their lower quantum energy compared to IR and higher frequency compared to microwave range allows for many potential applications unique to them. Especially in the security side of the THz sensing applications, the distinct absorption spectra of explosives and related compounds in the range of 0.1-5 THz makes THz technology a competitive technique for detecting hidden explosives. A compact, high power, room temperature continuous wave terahertz source emitting in a wide frequency range will greatly boost the THz applications for the diagnosis and detection of explosives. Here we present a new strong-coupled strain-balanced quantum cascade laser design for efficient THz generation based intracavity DFG. Room temperature continuous wave operation with electrical frequency tuning range of 2.06-4.35 THz is demonstrated.

18. Reflective THz and MR imaging of burn wounds: a potential clinical validation of THz contrast mechanisms

NASA Astrophysics Data System (ADS)

Bajwa, Neha; Nowroozi, Bryan; Sung, Shijun; Garritano, James; Maccabi, Ashkan; Tewari, Priyamvada; Culjat, Martin; Singh, Rahul; Alger, Jeffry; Grundfest, Warren; Taylor, Zachary

2012-10-01

Terahertz (THz) imaging is an expanding area of research in the field of medical imaging due to its high sensitivity to changes in tissue water content. Previously reported in vivo rat studies demonstrate that spatially resolved hydration mapping with THz illumination can be used to rapidly and accurately detect fluid shifts following induction of burns and provide highly resolved spatial and temporal characterization of edematous tissue. THz imagery of partial and full thickness burn wounds acquired by our group correlate well with burn severity and suggest that hydration gradients are responsible for the observed contrast. This research aims to confirm the dominant contrast mechanism of THz burn imaging using a clinically accepted diagnostic method that relies on tissue water content for contrast generation to support the translation of this technology to clinical application. The hydration contrast sensing capabilities of magnetic resonance imaging (MRI), specifically T2 relaxation times and proton density values N(H), are well established and provide measures of mobile water content, lending MRI as a suitable method to validate hydration states of skin burns. This paper presents correlational studies performed with MR imaging of ex vivo porcine skin that confirm tissue hydration as the principal sensing mechanism in THz burn imaging. Insights from this preliminary research will be used to lay the groundwork for future, parallel MRI and THz imaging of in vivo rat models to further substantiate the clinical efficacy of reflective THz imaging in burn wound care.

19. Millimeter wave and terahertz dielectric properties of biological materials

NASA Astrophysics Data System (ADS)

Khan, Usman Ansar

Broadband dielectric properties of materials can be employed to identify, detect, and characterize materials through their unique spectral signatures. In this study, millimeter wave, submillimeter wave, and terahertz dielectric properties of biological substances inclusive of liquids, solids, and powders were obtained using Dispersive Fourier Transform Spectroscopy (DFTS). Two broadband polarizing interferometers were constructed to test materials from 60 GHz to 1.2 THz. This is an extremely difficult portion of the frequency spectrum to obtain a material's dielectric properties since neither optical nor microwave-based techniques provide accurate data. The dielectric characteristics of liquids such as cyclohexane, chlorobenzene, benzene, ethanol, methanol, 1,4 dioxane, and 10% formalin were obtained using the liquid interferometer. Subsequently the solid interferometer was utilized to determine the dielectric properties of human breast tissues, which are fixed and preserved in 10% formalin. This joint collaboration with the Tufts New England Medical Center demonstrated a significant difference between the dielectric response of tumorous and non-tumorous breast tissues across the spectrum. Powders such as anthrax, flour, talc, corn starch, dry milk, and baking soda have been involved in a number of security threats and false alarms around the globe in the last decade. To be able to differentiate hoax attacks and serious security threats, the dielectric properties of common household powders were also examined using the solid interferometer to identify the powders' unique resonance peaks. A new sample preparation kit was designed to test the powder specimens. It was anticipated that millimeter wave and terahertz dielectric characterization will enable one to clearly distinguish one powder from the other; however most of the powders had relatively close dielectric responses and only Talc had a resonance signature recorded at 1.135 THz. Furthermore, due to

20. Detectivity enhancement in THz electrooptical sampling

SciTech Connect

Ahmed, Saima; Savolainen, Janne; Hamm, Peter

2014-01-15

We demonstrate and discuss a simple scheme that significantly enhances the detectivity of THz electro-optical sampling by introducing a sequence of Brewster windows that increases the ellipticity of the probe beam. By varying the window material or the number of Brewster windows, the enhancement factor can be adjusted; we demonstrate an enhancement factor of ≈20 with four ZnSe Brewster windows. The scheme is particularly useful when very small THz fields are to be measured in connection with low-repetition rate amplified Ti:S laser systems.

1. Plasma shock waves excited by THz radiation

NASA Astrophysics Data System (ADS)

Rudin, S.; Rupper, G.; Shur, M.

2016-10-01

The shock plasma waves in Si MOS, InGaAs and GaN HEMTs are launched at a relatively small THz power that is nearly independent of the THz input frequency for short channel (22 nm) devices and increases with frequency for longer (100 nm to 1 mm devices). Increasing the gate-to-channel separation leads to a gradual transition of the nonlinear waves from the shock waves to solitons. The mathematics of this transition is described by the Korteweg-de Vries equation that has the single propagating soliton solution.

2. Development of a THz spectroscopic imaging system.

PubMed

Usami, M; Iwamoto, T; Fukasawa, R; Tani, M; Watanabe, M; Sakai, K

2002-11-07

We have developed a real-time THz imaging system based on the two-dimensional (2D) electro-optic (EO) sampling technique. Employing the 2D EO-sampling technique, we can obtain THz images using a CCD camera at a video rate of up to 30 frames per second. A spatial resolution of 1.4 mm was achieved. This resolution was reasonably close to the theoretical limit determined by diffraction. We observed not only static objects but also moving ones. To acquire spectroscopic information, time-domain images were collected. By processing these images on a computer, we can obtain spectroscopic images. Spectroscopy for silicon wafers was demonstrated.

3. Complex dielectric properties of anhydrous polycrystalline glucose in the terahertz region

NASA Astrophysics Data System (ADS)

Sun, P.; Liu, W.; Zou, Y.; Jia, Qiong Z.; Li, Jia Y.

2015-03-01

We utilized terahertz time-domain spectroscopy (THz-TDS) to investigate the complex dielectric properties of solid polycrystalline material of anhydrous glucose (D-(+)-glucose with purity >99.9%). THz transmission spectra of samples were measured from 0.2 to 2.2 THz. The samples were prepared into tablets with thicknesses of 0.362, 0.447, 0.504, 0.522 and 0.626 mm, respectively. The imaginary part of the complex dielectric function of polycrystalline glucose showed that there were multiple characteristic absorption peaks at 1.232, 1.445, 1.522, 1.608, 1.811 and 1.987 THz, respectively. Moreover, for a given characteristic absorption peak, the real part of the complex dielectric function showed anomalous dispersion within the full width half maximum (FWHM) of the absorption peak. Both finite difference time-domain (FDTD) numerical simulations and experimental results showed that the complex dielectric function of anhydrous polycrystalline glucose fits well with the Lorentz dielectric mode. The plasma oscillation frequency was below the frequency of the light waves suggesting that the light waves passed through the polycrystalline glucose tablets. Calculations based on density functional theory (DFT) showed that the characteristic absorption peaks of polycrystalline glucose originated mainly from collective intermolecular vibrations such as hydrogen bonds and crystal phonon modes. The THz radiation can excite the vibrational or rotational energy levels of the biological macromolecules. This leads to changes in their spatial configuration or interactions. This study showed that THz-TDS has potential applications in biological and pharmaceutical research and food industry.

4. THz remote sensing for water vapor and cloud observation

NASA Astrophysics Data System (ADS)

Kasai, Yasuko; Ochiai, Satoshi; Mendrok, Jana; Baron, Philippe; Seta, Takamasa; Irimajiri, Yoshihisa

Terahertz (THz) region (0.1-20 THz; 3.3-650 cm-1 ) plays important role for the Earth's radiation budget, for example, 1) Up to 75% of atmospheric OLR is beyond 650 cm-1 (19.5 THz). 2) Up to 50% of basic greenhouse effect, mainly due to the water vapor, is in THz/Far-IR. 3) Clear-sky cooling of free troposphere occurs in THz/far-IR. 4) Upper tropospheric H2O radiative feedback occurs THz/far-IR. Atmospheric radiation in THz-wave region is characterised by the emission from water vapour. In other word, THz radiation is favorable frequency for the remote sensing observation of water vapor. Furthermore, THz-wave might be powerful method to observe ice cloud because of the sensitivity of ice cloud in this frequency, example, the average size of the ice cloud -100micron is consistent to 3THz. Despite the importance for water vapor and ice cloud observation, there are not many observation so far, and still poor knowledge in the atmosphere. Main reason was the lack of the THz technology for the remote sensing observation in this frequency region. We are developing an NICT THz-wave remote sensing system to observe planetary atmosphere. Three researches are currently in progress: 1) Development of the THz-wave radiative transfer model both for clear and cloudy sky including laboratory experiment. 2) Feasibility study for satellite system 3) Development of the ground-based observation system for the demonstration in the city air. We will present the recent status of the THz remote sensing project in NICT, particularly the feasibility study for the water vapor and cloud observation system in THz-wave region from ground-based, air-borne, and satellite born system.

5. Non Destructive Thermal Analysis and In Situ Investigation of Creep Mechanism of Graphite and Ceramic Composites using Phase-sensitive THz Imaging & Nonlinear Resonant Ultrasonic Spectroscopy

SciTech Connect

Zhang, XI-Cheng; Hurley, David; Redo-Scanchez, Albert

2012-11-26

In this project, we conducted a comprehensive study on nuclear graphite properties with terahertz (THz) imaging. Graphite samples from Idaho National Laboratory were carefully imaged by continuous wave (CW) THz. The CW THz imaging of graphite shows that the samples from different billet with different fabricating conditions have different pore size and structure. Based on this result, we then used a phase sensitive THz system to study the graphite properties. In this exploration, various graphite were studied. By imaging nuclear graphite samples in reflection mode at nine different incident polarization angles using THz time-domain spectroscopy, we find that different domain distributions and levels of porosity will introduce polarization dependence in THz reflectivity. Sample with higher density is less porous and has a smaller average domain distribution. As a consequence, it is less polarization-dependent and the polarization-dependent frequency is higher. The results also show that samples oxidized at higher temperatures tend to be more polarization dependent. The graphite from the external billet is more polarization dependent compared to that from the center billet. In addition, we performed laser-based ultrasonic measurements on these graphite samples. The denser, unoxidized samples allow surface acoustic waves to propagate more rapidly than in the samples that had already undergone oxidation. Therefore, for the oxidized samples, the denser samples show less polarization-dependence, higher polarization-dependent frequency, and allow the surface acoustic waves propagate faster.

6. Photonic-integrated circuit for continuous-wave THz generation.

PubMed

Theurer, Michael; Göbel, Thorsten; Stanze, Dennis; Troppenz, Ute; Soares, Francisco; Grote, Norbert; Schell, Martin

2013-10-01

We demonstrate a photonic-integrated circuit for continuous-wave (cw) terahertz (THz) generation. By comprising two lasers and an optical phase modulator on a single chip, the full control of the THz signal is enabled via a unique bidirectional operation technique. Integrated heaters allow for continuous tuning of the THz frequency over 570 GHz. Applied to a coherent cw THz photomixing system operated at 1.5 μm optical wavelength, we reach a signal-to-noise ratio of 44 dB at 1.25 THz, which is identical to the performance of a standard system based on discrete components.

7. Research on THz stepped-frequency ISAR imaging

NASA Astrophysics Data System (ADS)

Liang, Meiyan; Zhang, Zhiheng; Zhang, Cunlin

2016-11-01

High resolution THz inverse synthetic aperture radar (ISAR) imaging for the aircraft is simulated using 0.22THz stepped-frequency (SF) radar system which is designed in the paper. Based on the small rotate angle and the far field approximation, the Range-Doppler algorithm is proposed to reconstruct THz ISAR image of the aircraft. The simulation results indicate that THz stepped-frequency radar can achieve high resolution ISAR images of the aircraft, the resolution of the ISAR images can reach centimeter-scale, which laid a theoretical foundation for radar imaging in THz band.

8. Very High Power THz Radiation Sources.

PubMed

Carr, G L; Martin, M C; McKinney, W R; Jordan, K; Neil, G R; Williams, G P

2003-06-01

We report the production of high power (20watts average, ∼ 1 Megawatt peak) broadbandTHz light based on coherent emission fromrelativistic electrons. Such sources areideal for imaging, for high power damagestudies and for studies of non-linearphenomena in this spectral range. Wedescribe the source, presenting theoreticalcalculations and their experimentalverification. For clarity we compare thissource with one based on ultrafast lasertechniques.

9. Strong-Field THz Interactions with Wavepackets

NASA Astrophysics Data System (ADS)

Bucksbaum, Philip H.

1998-03-01

Intense THz radiation from photoconducting antennas are particularly useful for manipulating the structure and dynamics of atomic and molecular Rydberg states. We have used sub-picosecond half-cycle'' field pulses to follow both the radial(C. Raman, C.W.S. Conover, C.I. Sukenik, and P. H. Bucksbaum, Physical Review Letters 76), 2436 (1996). and angular motion(C.S. Raman, T.C. Weinacht, and P.H. Bucksbaum, Physical Review A 55), R3995-8 (1997). of wavepackets. The impulse imparted to an atomic electron by these pulses can also be used to produce or alter wavepacket motion. The THz radiation can be shaped by modulating optical radiation which photo-excites the antenna.(A. S. Weling et al., Appl. Phys. Lett. 64), 137, 1994. In this way we have produced intense tunable narrow-band THz radiation, which was employed to study population transfer in strongly driven Rydberg systems.(C. Raman, M. F. DeCamp and P. H. Bucksbaum, Optics Express 1) 186 (1997). The same techniques is used to arbitrarily adjust the intensity envelope of the THz pulse, alter its central frequency over a wide range, and to produce and control dispersion. When combined with active pulse-shaping and adaptive feedback techniques, wavepacket shapes and dispersion properties can be controlled.

10. Analysis of porous silicon

NASA Astrophysics Data System (ADS)

Earwaker, L. G.; Farr, J. P. G.; Grzeszczyk, P. E.; Sturland, I.; Keen, J. M.

1985-06-01

Porous silicon, suitable after oxidation for dielectric isolation, has been produced successfully by anodizing silicon in strong HF. The oxidized layer has been shown to have promise in device manufacture, providing high packing densities and radiation hardness. Anodizing has been carried out using both single and double cells, following the effects of current density. HF concentration and silicon resistivity. The resultant porous layers have been characterised with respect to composition and structure. The materials produced differ considerably in lattice strain, composition and reactivities. Prompt radiation analyses 19F(p,αγ), 16O(d,α), 12C(d,p), are useful for monitoring the anodizing procedures and subsequent oxidation: currently, interest centres on the mechanistic information obtained. RBS analysis using α-particles gives a much lower Si response from porous than from bulk silicon. Glancing angle proton recoil analyses reveal considerable quantities of hydrogen in the porous layers. These mutually consistent findings have considerable mechanistic significance; extensive Si-H bonding occurs following a 2 equivalent Faradaic process.

11. Subwavelength silicon through-hole arrays as an all-dielectric broadband terahertz gradient index metamaterial

SciTech Connect

Park, Sang-Gil; Jeong, Ki-Hun; Lee, Kanghee; Han, Daehoon; Ahn, Jaewook

2014-09-01

Structuring at subwavelength scales brings out artificial media with anomalous optical features called metamaterials. All-dielectric metamaterials have high potential for practical applications over the whole electromagnetic spectrum owing to low loss and optical isotropy. Here, we report subwavelength silicon through-hole arrays as an all-dielectric gradient index metamaterial with broadband THz operation. The unit cell consists of a single subwavelength through-hole on highly resistive monocrystalline silicon. Depending on the fill-factor and period, the effective index was linearly modulated at 0.3–1.6 THz. The experimental results also demonstrate silicon gradient refractive index (Si-GRIN) lenses with parabolic index profiles through the spatial modification of a single unit cell along the radial direction. Si-GRIN lenses either focus 0.4–1.6 THz beam to the diffraction-limit or serve as a flat and thin solid immersion lens on the backside of THz photoconductive antenna for highly efficient pulse extraction. This all-dielectric gradient index metamaterial opens up opportunities for integrated THz GRIN optics.

12. Nanotechnology-supported THz medical imaging

PubMed Central

Stylianou, Andreas; Talias, Michael A

2013-01-01

Over the last few decades, the achievements and progress in the field of medical imaging have dramatically enhanced the early detection and treatment of many pathological conditions. The development of new imaging modalities, especially non-ionising ones, which will improve prognosis, is of crucial importance. A number of novel imaging modalities have been developed but they are still in the initial stages of development and serious drawbacks obstruct them from offering their benefits to the medical field. In the 21 st century, it is believed that nanotechnology will highly influence our everyday life and dramatically change the world of medicine, including medical imaging. Here we discuss how nanotechnology, which is still in its infancy, can improve Terahertz (THz) imaging, an emerging imaging modality, and how it may find its way into real clinical applications. THz imaging is characterised by the use of non-ionising radiation and although it has the potential to be used in many biomedical fields, it remains in the field of basic research. An extensive review of the recent available literature shows how the current state of this emerging imaging modality can be transformed by nanotechnology. Innovative scientific concepts that use nanotechnology-based techniques to overcome some of the limitations of the use of THz imaging are discussed. We review a number of drawbacks, such as a low contrast mechanism, poor source performance and bulky THz systems, which characterise present THz medical imaging and suggest how they can be overcome through nanotechnology. Better resolution and higher detection sensitivity can also be achieved using nanotechnology techniques. PMID:24555052

13. Substrate independence of THz vibrational modes of polycrystalline thin films of molecular solids in waveguide THz-TDS

NASA Astrophysics Data System (ADS)

Harsha, S. Sree; Melinger, Joseph. S.; Qadri, S. B.; Grischkowsky, D.

2012-01-01

The influence of the metal substrate on the measurement of high resolution THz vibrational modes of molecular solids with the waveguide THz-TDS technique is investigated. The sample film of salicylic acid is studied using waveguide THz-TDS on three different metal substrates and two-surface passivated substrates. The independence of the observed THz vibrational modes to the metal substrate is demonstrated. Independently, surface passivation is presented as a viable experimental addition to the waveguide THz-TDS technique to aid the characterization of samples with known reactivity to metal surfaces.

14. Novel materials, fabrication techniques and algorithms for microwave and THz components, systems and applications

NASA Astrophysics Data System (ADS)

Liang, Min

This dissertation presents the investigation of several additive manufactured components in RF and THz frequency, as well as the applications of gradient index lens based direction of arrival (DOA) estimation system and broadband electronically beam scanning system. Also, a polymer matrix composite method to achieve artificially controlled effective dielectric properties for 3D printing material is studied. Moreover, the characterization of carbon based nano-materials at microwave and THz frequency, photoconductive antenna array based Terahertz time-domain spectroscopy (THz-TDS) near field imaging system, and a compressive sensing based microwave imaging system is discussed in this dissertation. First, the design, fabrication and characterization of several 3D printed components in microwave and THz frequency are presented. These components include 3D printed broadband Luneburg lens, 3D printed patch antenna, 3D printed multilayer microstrip line structure with vertical transition, THz all-dielectric EMXT waveguide to planar microstrip transition structure and 3D printed dielectric reflectarrays. Second, the additive manufactured 3D Luneburg Lens is employed for DOA estimation application. Using the special property of a Luneburg lens that every point on the surface of the Lens is the focal point of a plane wave incident from the opposite side, 36 detectors are mounted around the surface of the lens to estimate the direction of arrival (DOA) of a microwave signal. The direction finding results using a correlation algorithm show that the averaged error is smaller than 1º for all 360 degree incident angles. Third, a novel broadband electronic scanning system based on Luneburg lens phased array structure is reported. The radiation elements of the phased array are mounted around the surface of a Luneburg lens. By controlling the phase and amplitude of only a few adjacent elements, electronic beam scanning with various radiation patterns can be easily achieved

15. Design and research for biosensing THz microfluidic chips

NASA Astrophysics Data System (ADS)

Fan, Ning; Su, Bo; Zhang, Cong; Zhang, Cunlin

2016-11-01

Many Biomolecules vibration frequencies are in terahertz (0.1THz-10THz) frequency range, so terahertz (THz) technology is an essential tool for detecting biological molecules. However, due to terahertz strongly absorbed by water, it is difficult to detect these molecules for biological and chemical liquid samples. Therefore, we present a novel detection method by combining terahertz technology with microfluidic technology. The strong absorption of water is effectively overcome by controlling the length that terahertz passes through liquid samples. What's more, a higher signal to noise ratio is obtained through using less samples. In this paper, we designed a THz microfluidic chip that is easy to be fabricated by using the materials of Zeonor and polydimethylsiloxane (PDMS). Using terahertz time-domainspectroscopy (THz-TDS) system, we find that the chip has a high transmittance above 80% in the range from 0.2 THz to 2.6 THz. Then the THz spectra of deionized water and different kinds of solutions with different concentrations in the microfluidic chip were measured, respectively. In our research, it is found that different kinds of solutions have different transmission coefficients for THz. In addition, the THz transmission and absorption spectrum changes with the concentration of the same kind of solution.

16. Invited Article: Single-shot THz detection techniques optimized for multidimensional THz spectroscopy

SciTech Connect

Teo, Stephanie M.; Ofori-Okai, Benjamin K.; Werley, Christopher A.; Nelson, Keith A.

2015-05-15

Multidimensional spectroscopy at visible and infrared frequencies has opened a window into the transfer of energy and quantum coherences at ultrafast time scales. For these measurements to be performed in a manageable amount of time, one spectral axis is typically recorded in a single laser shot. An analogous rapid-scanning capability for THz measurements will unlock the multidimensional toolkit in this frequency range. Here, we first review the merits of existing single-shot THz schemes and discuss their potential in multidimensional THz spectroscopy. We then introduce improved experimental designs and noise suppression techniques for the two most promising methods: frequency-to-time encoding with linear spectral interferometry and angle-to-time encoding with dual echelons. Both methods, each using electro-optic detection in the linear regime, were able to reproduce the THz temporal waveform acquired with a traditional scanning delay line. Although spectral interferometry had mediocre performance in terms of signal-to-noise, the dual echelon method was easily implemented and achieved the same level of signal-to-noise as the scanning delay line in only 4.5% of the laser pulses otherwise required (or 22 times faster). This reduction in acquisition time will compress day-long scans to hours and hence provides a practical technique for multidimensional THz measurements.

17. Photonic generation for multichannel THz wireless communication.

PubMed

Shams, Haymen; Fice, Martyn J; Balakier, Katarzyna; Renaud, Cyril C; van Dijk, Frédéric; Seeds, Alwyn J

2014-09-22

We experimentally demonstrate photonic generation of a multichannel THz wireless signal at carrier frequency 200 GHz, with data rate up to 75 Gbps in QPSK modulation format, using an optical heterodyne technique and digital coherent detection. BER measurements were carried out for three subcarriers each modulated with 5 Gbaud QPSK or for two subcarriers modulated with 10 Gbaud QPSK, giving a total speed of 30 Gbps or 40 Gbps, respectively. The system evaluation was also performed with three subcarriers modulated with 12.5 Gbaud QPSK (75 Gbps total) without and with 40 km fibre transmission. The proposed system enhances the capacity of high-speed THz wireless transmission by using spectrally efficient modulated subcarriers spaced at the baud rate. This approach increases the overall transmission capacity and reduces the bandwidth requirement for electronic devices.

18. Carbon Nanotube Quantum Dots as THz Detectors

DTIC Science & Technology

2012-12-14

devices that are viable for wafer -scale production. We recently started testing fabrication processes using epitaxial graphene on SiC in collaboration... laser sources at four different Fig. 4 Top: Drain current versus the gate voltage for different THz field intensities. Bottom: Temperature dependence...research. The first was the small coupling between the quantum dot and the powerful (10 mW) laser source. The second was the difficulty to reproduce the

19. Very high power THz radiation sources

SciTech Connect

Carr, G.L.; Martin, Michael C.; McKinney, Wayne R.; Jordan, K.; Neil, George R.; Williams, G.P.

2002-10-31

We report the production of high power (20 watts average, {approx} 1 Megawatt peak) broadband THz light based on coherent emission from relativistic electrons. Such sources are ideal for imaging, for high power damage studies and for studies of non-linear phenomena in this spectral range. We describe the source, presenting theoretical calculations and their experimental verification. For clarity we compare this source to one based on ultrafast laser techniques.

20. Very High Power THz Radiation Sources

SciTech Connect

G.L. Carr; Michael C. Martin; Wayne R. McKinney; Kevin Jordan; George R. Neil; Gwyn P. Williams

2002-10-01

We report the production of high power (20 watts average, {approx}1 Megawatt peak) broadband THz light based on coherent emission from relativistic electrons. Such sources are ideal for imaging, for high power damage studies and for studies of non-linear phenomena in this spectral range. We describe the source, presenting theoretical calculations and their experimental verification. For clarity, we compare this sources with one based on ultrafast laser techniques.

1. THz Emission Based On Intersubband Plasmon Resonances

SciTech Connect

Coquelin, M.; Zobl, R.; Strasser, G.; Gornik, E.; Bakshi, P.; Umansky, V.; Heiblum, M.

2010-01-04

The radiative decay of collective plasma oscillations as a new mechanism for THz emission is studied. This phenomenon is based on the attractive interaction of two intersubband plasmons. This interaction can be viewed as a collective e-e scattering phenomenon. The emission results fit very well to the results of the current voltage measurements indicating that the conditions for a plasma instability are reached.

2. Time-resolved THz studies of carrier dynamics in semiconductors, superconductors, and strongly-correlated electron materials

SciTech Connect

Kaindl, Robert A.; Averitt, Richard D.

2006-11-14

materials occur at lower energies. The terahertz (THz) regime is particularly rich in such fundamental resonances. This includes ubiquitous lattice vibrations and low-energy collective oscillations of conduction charges. In nanoscale materials, band structure quantization also yields novel infrared and THz transitions, including intersubband absorption in quantum wells. The formation of excitons in turn leads to low-energy excitations analogous to inter-level transitions in atoms. In transition-metal oxides, fundamental excitation gaps arise from charge pairing into superconducting condensates and other correlated states. This motivates the use of ultrafast THz spectroscopy as a powerful tool to study light-matter interactions and microscopic processes in nanoscale and correlated-electron materials.A distinct advantage of coherent THz pulses is that the amplitude and phase of the electric field can be measured directly, as the THz fields are coherent with the fs pulses from which they are generated. Using THz time-domain spectroscopy (THz-TDS), both the real and imaginary parts of the response functions (such as the dielectric function) are obtained directly without the need for Kramers?Kronig transforms. The THz response can also be expressed in terms of absorption and refractive index, or as the optical conductivity. The optical conductivity describes the current response of a many-body system to an electric field, an ideal tool to study conducting systems. A second important advantage is the ultrafast time resolution that results from the short temporal duration of the THz time-domain sources. In particular, optical-pump THz-probe spectroscopy enables a delicate probe of the transient THz conductivity after optical photoexcitation. These experiments can provide insight into quasiparticle interactions, phase transitions, or nonequilibrium dynamics. In this chapter we will provide many such examples. Since THz spectroscopy of solids is a quickly expanding field

3. THz polarization difference imaging of aqueous targets

NASA Astrophysics Data System (ADS)

Sung, Shijun; Bajwa, Neha; Ramirez, Lucia; Grundfest, Warren; Taylor, Zachary

2015-08-01

This paper describes the basic design, implementation, and testing of a polarization difference imaging system for use on aqueous targets. The ultimate performance limitation of THz imaging in many active areas of research is clutter from surface geometry. While the signal to nose ratio (SNR) of standard THz imaging systems is quite large, the signal to clutter ratio (SCR) often faced in an imaging application is orders of magnitude lower and, in many cases, lower than the contrast to noise (CNR) resulting in imagery where the contrast mechanism of interest does not significantly contribute to the overall observed contrast. To overcome these limitations we develop a system that uses a circularly polarized source and linearly polarized detectors to acquire images of transverse electric (TE) and transverse magnetic (TM) reflectivities of the target over the same field of view. Geletin based tissue mimicking phantoms are fabricated with spatially varying water content and modified with a range of surface topologies and surface roughness. TE and TM images are combined to yield self-calibrated clutter-suppressed images. The resulting image indicates that the imaging field clutter affected both polarization channels nearly equally allowing the system to resolve differences in phantom water content. This design is a step toward windowless THz imaging capability critical for clinical translation where patient imaging is dominated by clutter.

4. Multifrequency high precise subTHz-THz-IR spectroscopy for exhaled breath research

NASA Astrophysics Data System (ADS)

Vaks, Vladimir L.; Domracheva, Elena G.; Pripolzin, Sergey I.; Chernyaeva, Mariya B.

2016-09-01

Nowadays the development of analytical spectroscopy with high performance, sensitivity and spectral resolution for exhaled breath research is attended. The method of two-frequency high precise THz spectroscopy and the method of high precise subTHz-THz-IR spectroscopy are presented. Development of a subTHz-THz-IR gas analyzer increases the number of gases that can be identified and the reliability of the detection by confirming the signature in both THz and MIR ranges. The testing measurements have testified this new direction of analytical spectroscopy to open widespread trends of its using for various problems of medicine and biology. First of all, there are laboratory investigations of the processes in exhaled breath and studying of their dynamics. Besides, the methods presented can be applied for detecting intermediate and short time living products of reactions in exhaled breath. The spectrometers have been employed for investigations of acetone, methanol and ethanol in the breath samples of healthy volunteers and diabetes patients. The results have demonstrated an increased concentration of acetone in breath of diabetes patients. The dynamic of changing the acetone concentration before and after taking the medicines is discovered. The potential markers of pre-cancer states and oncological diseases of gastrointestinal tract organs have been detected. The changes in the NO concentration in exhaled breath of cancer patients during radiotherapy as well as increase of the NH3 concentration at gastrointestinal diseases have been revealed. The preliminary investigations of biomarkers in three frequency ranges have demonstrated the advantages of the multifrequency high precise spectroscopy for noninvasive medical diagnostics.

5. Dissociation of D2+ by UV and THz light pulses

NASA Astrophysics Data System (ADS)

Xu, Tian-Yu; He, Feng

2013-10-01

The dissociation of D2+ in the few-cycle UV and THz light pulses is studied by numerically simulating the time-dependent Schrödinger equation. With only the UV pulse, we find the dissociation probability does not increase monotonously with the increasing of the UV pulse intensity or duration. The UV-triggered dissociation is streaked by the time-delayed THz light pulse, i.e., the nuclear momentum oscillates with the half of the THz period when the UV-THz time delay or the carrier envelope phase of the THz pulse is scanned. The difference of the maximum and minimum nuclear momenta equals the THz laser vector potential. The classical calculation of the Newtonian equation for a mass point moving on the THz light-modified molecular potential curves reproduces the quantum simulation results and therefore intuitively explores the physical scenario: The nuclear wave packets propagate along the THz field-dressed molecular potential curves adiabatically but make a fully diabatic transition, while the THz electric field changes direction. This study offers a visual angle to understand the molecular dissociation in the strong laser field with very long wavelengths.

6. Substrate Independence of THz Vibrational Modes of Polycrystalline Thin Films of Molecular Solids in Waveguide THz-TDS

DTIC Science & Technology

2012-01-01

THz-TDS technique is investigated. The sample film of salicylic acid is studied using waveguide THz-TDS on three different metal substrates and two...vibrational modes with wave- guide THz-TDS. The investigation of substrate dependence is performed using salicylic acid as the test molecule. This...Al and a self assembled monolayer (SAM) on Au. Salicylic acid is first characterized in the pel- let form and then compared to the absorption features

7. 3D-Printed Broadband Dielectric Tube Terahertz Waveguide with Anti-Reflection Structure

NASA Astrophysics Data System (ADS)

Vogt, Dominik Walter; Leonhardt, Rainer

2016-11-01

We demonstrate broadband, low loss, and close-to-zero dispersion guidance of terahertz (THz) radiation in a dielectric tube with an anti-reflection structure (AR-tube waveguide) in the frequency range from 0.2 to 1.0 THz. The anti-reflection structure (ARS) consists of close-packed cones in a hexagonal lattice arranged on the outer surface of the tube cladding. The feature size of the ARS is in the order of the wavelength between 0.2 and 1.0 THz. The waveguides are fabricated with the versatile and cost efficient 3D-printing method. Terahertz time-domain spectroscopy (THz-TDS) measurements as well as 3D finite-difference time-domain simulations (FDTD) are performed to extensively characterize the AR-tube waveguides. Spectrograms, attenuation spectra, effective phase refractive indices, and the group-velocity dispersion parameters β 2 of the AR-tube waveguides are presented. Both the experimental and numerical results confirm the extended bandwidth and smaller group-velocity dispersion of the AR-tube waveguide compared to a low loss plain dielectric tube THz waveguide. The AR-tube waveguide prototypes show an attenuation spectrum close to the theoretical limit given by the infinite cladding tube waveguide.

8. Coherent detection of THz waves based on THz-induced time-resolved luminescence quenching in bulk gallium arsenide.

PubMed

Chu, Zheng; Liu, Jinsong; Wang, Kejia

2012-05-01

A kind of photoluminescence quenching, in which the time-resolved photoluminescence is modulated by a THz pulse, has been theoretically investigated by performing the ensemble Monte Carlo method in bulk gallium arsenide (GaAs) at room temperature. The quenching ratio could reach up to 50% under a strong THz field (100  kV/cm). The range in which luminescence quenching is linearly proportional to the THz field could be over 60  kV/cm. On the basis of these results, a principle for THz modulation and coherent detection is proposed.

9. Technology trend in real-time, uncooled image sensors for sub-THz and THz wave detection

NASA Astrophysics Data System (ADS)

Oda, Naoki

2016-05-01

The author summarizes development of uncooled microbolometer terahertz (THz) focal plane arrays (FPAs) and real-time cameras for sub-THz and THz wave detection. The array formats are 320x240 and 640x480, and the cameras have several functions, such as lock-in imaging, external-trigger imaging, image processing (pixel binning and frame integration), beam profiling and so on. The FPAs themselves are sensitive to sub-THz, THz and infrared radiations. Active imaging systems based on the imagers are described. One of them is a real-time transmission-type THz microscope which contains a THz camera and a quantum cascade laser (QCL). The other one is an active sub-THz imaging system, where a transmission imaging mode and a reflection imaging mode can be switched with one-touch operation. Strong THz emitters, such as far-infrared gas lasers and QCLs, are strongly coherent and often produce interference fringes in an image. A method of reducing the interference fringes (beam homogenizing) is described. Microbolometer FPAs developed by other groups, antenna-coupled CMOS FPA, array detectors based on GaAs high-mobility heterostructure and so on are also summarized, which operate in real-time and at room temperature. A fair method of evaluating performance of detectors with different sizes and at different wavelengths is explained and the performances of the detectors are compared.

10. Spectral Trends of Solar Bursts at Sub-THz Frequencies

NASA Astrophysics Data System (ADS)

Fernandes, L. O. T.; Kaufmann, P.; Correia, E.; Giménez de Castro, C. G.; Kudaka, A. S.; Marun, A.; Pereyra, P.; Raulin, J.-P.; Valio, A. B. M.

2017-01-01

Previous sub-THz studies were derived from single-event observations. We here analyze for the first time spectral trends for a larger collection of sub-THz bursts. The collection consists of a set of 16 moderate to small impulsive solar radio bursts observed at 0.2 and 0.4 THz by the Solar Submillimeter-wave Telescope (SST) in 2012 - 2014 at El Leoncito, in the Argentinean Andes. The peak burst spectra included data from new solar patrol radio telescopes (45 and 90 GHz), and were completed with microwave data obtained by the Radio Solar Telescope Network, when available. We critically evaluate errors and uncertainties in sub-THz flux estimates caused by calibration techniques and the corrections for atmospheric transmission, and introduce a new method to obtain a uniform flux scale criterion for all events. The sub-THz bursts were searched during reported GOES soft X-ray events of class C or larger, for periods common to SST observations. Seven out of 16 events exhibit spectral maxima in the range 5 - 40 GHz with fluxes decaying at sub-THz frequencies (three of them associated to GOES class X, and four to class M). Nine out of 16 events exhibited the sub-THz spectral component. In five of these events, the sub-THz emission fluxes increased with a separate frequency from that of the microwave spectral component (two classified as X and three as M), and four events have only been detected at sub-THz frequencies (three classified as M and one as C). The results suggest that the THz component might be present throughout, with the minimum turnover frequency increasing as a function of the energy of the emitting electrons. The peculiar nature of many sub-THz burst events requires further investigations of bursts that are examined from SST observations alone to better understand these phenomena.

11. THz optics and metamaterials: Design, fabrication and characterization

NASA Astrophysics Data System (ADS)

Turaga, Shuvan Prashant

In the past decade, terahertz(THz) based optics and metamaterials have been extensively researched to create components and devices in the frequency range of 0.1 to 5 THz also known as 'THz gap'. Metamaterials, in particular, have realized concepts such as negative refraction, slow light and superlensing through artificially engineered media. The naturally available materials have very weak interaction of terahertz light. Therefore, the design of THz metamaterials to manipulate THz radiation is an important task towards furthering the usage of terahertz light for practical applications. The thesis involved the development of two lab facilities for fabrication and characterization. A state-of-the-art two photon lithography( TPL) system was developed which enables us to manufacture 3D structures with sub-diffraction limit resolution(280nm at 800 nm wavelength). The software was written to enable easy fabrication of multiple structures with different algorithms. For characterizing our metamaterial structures in the terahertz regime, a THz time-domain spectroscopy(THz-TDS) and imaging system was built. This transmission based spectrometer has a dynamic range of 50 dB at 0.5 THz and a bandwidth of about 2.5 THz. To demonstrate the application of these home-built facilities, the metamaterials in the THz regime were fabricated using TPL and UV lithography. To investigate conductive coupling effects in meta-atoms, a new design was proposed, fabricated and characterized. As an application of TPL, free standing polymer helices were fabricated and coated with silver electroless plating. These silver helical metamaterials have potential application as circular polarizers in the MIR and THz regimes. The aspect ratio effects of these helical metamaterials were also studied in order to improve their polarizing performance.

12. Material Inspection Using THz and Thermal Wave

NASA Astrophysics Data System (ADS)

Zhang, Cunlin; Mu, Kaijun; Li, Yanhong; Zhang, X.-C.

2007-03-01

Terahertz (THz) and thermal wave imaging technologies are complementary inspection modalities for use in non-contact and non-destructive evaluation. Both of them are applied in order to evaluate damages on a variety of composite samples. We will also report the test of a large number of insulation foam panels used in NASA's External Fuel Tank through pulse and CW terahertz systems. The study of defects using the two techniques in selected materials, including metal plates, carbon fibers, glass fibers, carbon silicon composites, etc is also shown.

13. Silicon Micromachined Microlens Array for THz Antennas

NASA Technical Reports Server (NTRS)

Lee, Choonsup; Chattopadhyay, Goutam; Mehdi, IImran; Gill, John J.; Jung-Kubiak, Cecile D.; Llombart, Nuria

2013-01-01

5 5 silicon microlens array was developed using a silicon micromachining technique for a silicon-based THz antenna array. The feature of the silicon micromachining technique enables one to microfabricate an unlimited number of microlens arrays at one time with good uniformity on a silicon wafer. This technique will resolve one of the key issues in building a THz camera, which is to integrate antennas in a detector array. The conventional approach of building single-pixel receivers and stacking them to form a multi-pixel receiver is not suited at THz because a single-pixel receiver already has difficulty fitting into mass, volume, and power budgets, especially in space applications. In this proposed technique, one has controllability on both diameter and curvature of a silicon microlens. First of all, the diameter of microlens depends on how thick photoresist one could coat and pattern. So far, the diameter of a 6- mm photoresist microlens with 400 m in height has been successfully microfabricated. Based on current researchers experiences, a diameter larger than 1-cm photoresist microlens array would be feasible. In order to control the curvature of the microlens, the following process variables could be used: 1. Amount of photoresist: It determines the curvature of the photoresist microlens. Since the photoresist lens is transferred onto the silicon substrate, it will directly control the curvature of the silicon microlens. 2. Etching selectivity between photoresist and silicon: The photoresist microlens is formed by thermal reflow. In order to transfer the exact photoresist curvature onto silicon, there needs to be etching selectivity of 1:1 between silicon and photoresist. However, by varying the etching selectivity, one could control the curvature of the silicon microlens. The figure shows the microfabricated silicon microlens 5 x5 array. The diameter of the microlens located in the center is about 2.5 mm. The measured 3-D profile of the microlens surface has a

14. Novel Devices and Components for THz Systems

DTIC Science & Technology

2014-04-25

was output to free-space with a standard fiber-to-free-space coupler and then chopped at 8 Hz for easy THz power and photocurrent measurement. A 10x...motorStep = .0000925; motorSpeed = .000893; end % Variable list Loops = 1; num_channels = 1; ScanRate = 3; % Set scan rate buffer = 100; % 5...second buffer time Scans = (ScanRate/1000) * (time*1000)*2; global final_array; % Configure for 12-bit resolution 167 188 Error = ljud_AddRequest

15. Method for producing high dielectric strength microvalves

DOEpatents

Kirby, Brian J.; Reichmuth, David S.; Shepodd, Timothy J.

2006-04-04

A microvalve having a cast-in-place and lithographically shaped mobile, polymer monolith for fluid flow control in microfluidic devices and method of manufacture. The microvalve contains a porous fluorinated polymer monolithic element whose pores are filled with an electrically insulating, high dielectric strength fluid, typically a perfluorinated liquid. This combination provides a microvalve that combines high dielectric strength with extremely low electrical conductivity. These microvalves have been shown to have resistivities of at least 100 G.OMEGA. and are compatible with solvents such as water at a pH between 2.7 and 9.0, 1-1 propanol, acetonitrile, and acetone.

16. A scanned beam THz imaging system for medical applications

NASA Astrophysics Data System (ADS)

Taylor, Zachary D.; Li, Wenzao; Suen, Jon; Tewari, Priyamvada; Bennett, David; Bajwa, Neha; Brown, Elliott; Culjat, Martin; Grundfest, Warren; Singh, Rahul

2011-10-01

THz medical imaging has been a topic of increased interest recently due largely to improvements in source and detector technology and the identification of suitable applications. One aspect of THz medical imaging research not often adequately addressed is pixel acquisition rate and phenomenology. The majority of active THz imaging systems use translation stages to raster scan a sample beneath a fixed THz beam. While these techniques have produced high resolution images of characterization targets and animal models they do not scale well to human imaging where clinicians are unwilling to place patients on large translation stages. This paper presents a scanned beam THz imaging system that can acquire a 1 cm2 area with 1 mm2 pixels and a per-pixel SNR of 40 dB in less than 5 seconds. The system translates a focused THz beam across a stationary target using a spinning polygonal mirror and HDPE objective lens. The illumination is centered at 525 GHz with ~ 125 GHz of response normalized bandwidth and the component layout is designed to optically co-locate the stationary source and detector ensuring normal incidence across a 50 mm × 50 mm field of view at standoff of 190 mm. Component characterization and images of a test target are presented. These results are some of the first ever reported for a short standoff, high resolution, scanned beam THz imaging system and represent an important step forward for practical integration of THz medical imaging where fast image acquisition times and stationary targets (patients) are requisite.

17. THz transceiver characterization : LDRD project 139363 final report.

SciTech Connect

Nordquist, Christopher Daniel; Wanke, Michael Clement; Cich, Michael Joseph; Reno, John Louis; Fuller, Charles T.; Wendt, Joel Robert; Lee, Mark; Grine, Albert D.

2009-09-01

LDRD Project 139363 supported experiments to quantify the performance characteristics of monolithically integrated Schottky diode + quantum cascade laser (QCL) heterodyne mixers at terahertz (THz) frequencies. These integrated mixers are the first all-semiconductor THz devices to successfully incorporate a rectifying diode directly into the optical waveguide of a QCL, obviating the conventional optical coupling between a THz local oscillator and rectifier in a heterodyne mixer system. This integrated mixer was shown to function as a true heterodyne receiver of an externally received THz signal, a breakthrough which may lead to more widespread acceptance of this new THz technology paradigm. In addition, questions about QCL mode shifting in response to temperature, bias, and external feedback, and to what extent internal frequency locking can improve stability have been answered under this project.

18. Comparative Study of Solar Bursts at Sub-THz Frequencies

NASA Astrophysics Data System (ADS)

Fernandes, L. O. T.; Kaufmann, P.; Correia, E.; Marun, A.; Pereyra, P.; Raulin, J.-P.; Valio, A. B. M.

2016-04-01

We analyze a large set of 17 solar radio bursts observed at sub-THz (0.2 and 0.4 THz) in 2012-2014 together with the new solar patrol radio telescopes (45 and 90 GHz), operated at El Leoncito, in the Argentinean Andes, allowing the derivation of complete burst spectra in this unexplored range of frequencies. We discuss the uncertainties in sub-THz flux estimates caused by calibration techniques and the corrections for atmospheric transmission. The burst spectra were completed with microwave bursts data obtained by the Radio Solar Telescope Network - RSTN. The events selection was based on GOES soft X-rays burst reported for classes stronger then C. Nearly 50 percent of the bursts exhibited a frequency increasing sub-THz spectral component. The results suggest that the THz component might be always present, with the minimum turn-over frequencies shifting to higher frequencies for larger energies of the electrons producing the emissions.

19. [Study on THz spectra of nicotinic acid, nicotinamide and nicotine].

PubMed

Yu, Bin; Huang, Zhen; Wang, Xiao-yan; Zhao, Guo-zhong

2009-09-01

The terahertz (THz) spectra of nicotinic acid, nicotinamide and nicotine were studied at room temperature. The time-domain THz spectra were measured. The frequency-domain spectra were obtained by fast Fourier transform (FFT). The spectral response and the dispersive relationship of refractive index in THz spectral range were obtained. The results show that the samples have obvious spectral response in THz spectral range except nicotine. The corresponding stimulated spectra were given by using density functional theory (DFT) method for both nicotinamide and nicotinic acid. The origin of the absorption peaks of nicotinic acid and nicotinamide was explored. It is thought that the absorption peak of nicotinic acid is caused by the torsion and wagging of the molecule, but the absorption peaks of nicotinamide (except 1.93 THz) are caused by intermolecular or phonon mode. It was shown that the molecule structure and vibrational modes of nicotinic acid and nicotinamide can be analyzed by the combination of simulation and experimental results.

20. Application of porous silicon in terahertz technology

NASA Astrophysics Data System (ADS)

Lo, Shu-Zee Alencious

In this thesis, we discuss our efforts in developing porous silicon based devices for terahertz signal processing. In the first stage of our research, we demonstrate that porous silicon samples fabricated from highly doped p-type silicon can have adjustable refractive indices ranging from 1.5--2.1 and can exhibit a resistivity that is four orders of magnitude higher than that of the silicon wafer from which they were made. We show that the porous silicon becomes stable and relatively lossless after thermal oxidation. The partially oxidized porous silicon is shown to exhibit a smooth absorption spectrum, with low absorption loss of <10 cm-1 over the entire terahertz spectrum. As a proof of concept, we fabricated, for the first time, a porous silicon based multilayered Bragg filter with reflectance of 93% and full-width at half-maximum bandwidth of 0.26 THz. Compared with other multilayered filtering techniques, porous silicon has the advantage that it can be easily fabricated, and offers the possibility of forming multilayer and graded index structures for more advanced filters. The large surface area of nanoporous silicon makes it an especially attractive platform for applications in biochemical detection and diagnostics As part of our effort in developing terahertz waveguide for biosensing, we reported the world's first porous silicon based terahertz waveguide using the principle of surface plasmon polaritons. The effect of porous silicon film thickness on the propagation of surface plasmons is explained theoretically in this thesis and is found to be in good agreement with experimental results.

1. The mechanism of the dielectric relaxation in water.

PubMed

Popov, Ivan; Ishai, Paul Ben; Khamzin, Airat; Feldman, Yuri

2016-05-18

Although relating to the same system, the interpretations of the water spectra from Raman and Dielectric spectroscopy present independent pictures of the nature of water. We show that in the overlap region of the two methods it is possible to combine these views into a coherent concept of what drives the dynamic features of water. In this work, we develop the idea that the dielectric relaxation in water is driven by the migration of defects through the H-bond network, leading to a Debye-like peak in the lower frequencies. The deviation from the Debye law in the higher sub-THz frequencies is traced to a global fluctuation of the same H-bond network, clearly evident in the Raman Spectra. By incorporating these two views, a mathematical formalism is presented that can aptly explicate the dielectric spectra of liquid water.

2. THz characterization of lysozyme at different conformations

NASA Astrophysics Data System (ADS)

Globus, Tatiana; Khromova, Tatyana; Lobo, Rebecca; Woolard, Dwight; Swami, Nathan; Fernandez, Erik

2005-05-01

This work demonstrates application of Fourier Transform Infrared Spectroscopy (FTIR) technique in the low terahertz frequency range of 10-25 cm-1 to discriminate between different protein conformations and evaluate possible application of THz spectroscopy for monitoring of protein folding-unfolding process. A specific procedure developed earlier for unfolding lysozyme by salt (KSCN) precipitation and refolding the lysozyme molecules by removing of KSCN and dissolving in sodium acetate was used to prepare three different forms of lysozyme. In addition, two standard procedures were used to prepare samples in unfolded conformation: denaturation at high temperature ~95° C followed by fast freezing, and dissolution in 6 M guanidine. Thin, air dried protein films were characterized as well as material in the form of gel. Spectra reveal resonance features in transmission which represent vibrational modes in the protein samples. A great variability of spectral features for the different conformational states showed the sensitivity of vibrational frequencies to the three dimensional structure of proteins. The results obtained on liquid (gel) samples indicate that THz transmission spectroscopy can be used for monitoring folding-unfolding process in a realistic, aqueous environment.

3. Micromachined TWTs for THz Radiation Sources

NASA Technical Reports Server (NTRS)

Booske, John H.; vanderWeide, Daniel W.; Kory, Carol L.; Limbach, S.; Downey, Alan (Technical Monitor)

2001-01-01

The Terahertz (THz) region of the electromagnetic spectrum (about 300 - 3000 GHz in frequency or about 0.1 - 1 mm free space wavelength) has enormous potential for high-data-rate communications, spectroscopy, astronomy, space research, medicine, biology, surveillance, remote sensing, industrial process control, etc. It has been characterized as the most scientifically rich, yet under-utilized, region of the electromagnetic spectrum. The most critical roadblock to full exploitation of the THz band is lack of coherent radiation sources that are powerful (0.001 - 1.0 W continuous wave), efficient (> 1%), frequency agile (instantaneously tunable over 1% bandwidths or more), reliable, and comparatively inexpensive. To develop vacuum electron device (VED) radiation sources satisfying these requirements, fabrication and packaging approaches must be heavily considered to minimize costs, in addition to the basic interaction physics and circuit design. To minimize size of the prime power supply, beam voltage must be minimized, preferably 10 kV. Solid state sources satisfy the low voltage requirement, but are many orders of magnitude below power, efficiency, and bandwidth requirements. On the other hand, typical fast-wave VED sources in this regime (e.g., gyrotrons, FELs) tend to be large, expensive, high voltage and very high power devices unsuitable for most of the applications cited above. VEDs based on grating or inter-digital (ID) circuits have been researched and developed. However, achieving forward-wave amplifier operation with instantaneous fractional bandwidths > 1% is problematic for these devices with low-energy (< 15 kV) electron beams. Moreover, the interaction impedance is quite low unless the beam-circuit spacing is kept particularly narrow, often leading to significant beam interception. One solution to satisfy the THz source requirements mentioned above is to develop micromachined VEDs, or "micro-VEDs". Among other benefits, micro-machining technologies

4. Dielectric properties of amorphous phase-change materials

NASA Astrophysics Data System (ADS)

Chen, C.; Jost, P.; Volker, H.; Kaminski, M.; Wirtssohn, M.; Engelmann, U.; Krüger, K.; Schlich, F.; Schlockermann, C.; Lobo, R. P. S. M.; Wuttig, M.

2017-03-01

The dielectric function of several amorphous phase-change materials has been determined by employing a combination of impedance spectroscopy (9 kHz-3 GHz) and optical spectroscopy from the far- (20 c m-1 , 0.6 THz) to the near- (12 000 c m-1 , 360 THz) infrared, i.e., from the DC limit to the first interband transition. While phase-change materials undergo a change from covalent bonding to resonant bonding on crystallization, the amorphous and crystalline phases of ordinary chalcogenide semiconductors are both governed by virtually the same covalent bonds. Here, we study the dielectric properties of amorphous phase-change materials on the pseudobinary line between GeTe and S b2T e3 . These data provide important insights into the charge transport and the nature of bonding in amorphous phase-change materials. No frequency dependence of permittivity and conductivity is discernible in the impedance spectroscopy measurements. Consequently, there are no dielectric relaxations. The frequency-independent conductivity is in line with charge transport via extended states. The static dielectric constant significantly exceeds the optical dielectric constant. This observation is corroborated by transmittance measurements in the far infrared, which show optical phonons. From the intensity of these phonon modes, a large Born effective charge is derived. Nevertheless, it is known that crystalline phase-change materials such as GeTe possess even significantly larger Born effective charges. Crystallization is hence accompanied by a huge increase in the Born effective charge, which reveals a significant change of bonding upon crystallization. In addition, a clear stoichiometry trend in the static dielectric constant along the pseudobinary line between GeTe and S b2T e3 has been identified.

5. Magnetic Fano resonances by design in symmetry broken THz meta-foils

NASA Astrophysics Data System (ADS)

Wu, Jianfeng; Moser, Herbert O.; Li, Rujiang; Yang, Yihao; Jing, Liqiao; Chen, Hongsheng; Breese, Mark B. H.

2017-02-01

Magnetic Fano resonances in there-dimensional symmetry broken meta-foils at THz frequencies are theoretically and experimentally studied. Sharp Fano resonances occur due to the interference between different resonances and can be designed by choosing geometric parameters of the meta-foil. At the Fano resonances, the meta-foil supports antisymmetric modes, whereas, at the main resonance, only a symmetric mode exists. The meta-foil is left-handed at the Fano resonances and shows sharp peaks of the real part of the refractive index in transmission with small effective losses opening a way to very sensitive high-speed sensing of dielectric changes in the surrounding media and of mechanical configuration.

6. Magnetic Fano resonances by design in symmetry broken THz meta-foils

PubMed Central

Wu, Jianfeng; Moser, Herbert O.; Li, Rujiang; Yang, Yihao; Jing, Liqiao; Chen, Hongsheng; Breese, Mark B. H.

2017-01-01

Magnetic Fano resonances in there-dimensional symmetry broken meta-foils at THz frequencies are theoretically and experimentally studied. Sharp Fano resonances occur due to the interference between different resonances and can be designed by choosing geometric parameters of the meta-foil. At the Fano resonances, the meta-foil supports antisymmetric modes, whereas, at the main resonance, only a symmetric mode exists. The meta-foil is left-handed at the Fano resonances and shows sharp peaks of the real part of the refractive index in transmission with small effective losses opening a way to very sensitive high-speed sensing of dielectric changes in the surrounding media and of mechanical configuration. PMID:28150797

7. Temperature-dependent time-domain THz spectroscopic study of spinel NiCo2O4 thin films

NASA Astrophysics Data System (ADS)

Silwal, Punam; Shan, Tianqi; Kim, Daeho; Talbayev, Diyar

2013-03-01

The unique combination of electrical conductivity, infrared transparency, electro catalytic activity, and ferrimagnetic order makes the spinel NiCo2O4 an attractive material for various technological applications. Our previous study showed that high quality epitaxial spinel NiCo2O4 films on MgAl2O4 (001) substrate exhibit metallic behavior accompanied by ferrimagnetic order. The electrical properties of these films can be tuned from metallic to insulating by changing the growth temperature. The comprehensive understanding of the microscopic details of carrier transport in these films requires the study of frequency-dependent optical properties. Terahertz time-domain spectroscopy (THz TDS) can determine the frequency dependent complex dielectric constant, refractive index, and optical conductivity. We used THz TDS to measure the optical properties of NiCo2O4 in the 0.2 - 2.7 THz spectral region. The complex conductivities display a Drude-type frequency response. The extrapolated DC conductivity is consistent with our previous work. The temperature- and growth-condition dependent Drude parameters provide further insight in the metal-insulator transition in these materials.

8. Dielectric metasurfaces

NASA Astrophysics Data System (ADS)

Valentine, Jason

While plasmonics metasurfaces have seen much development over the past several years, they still face throughput limitations due to ohmic losses. On the other hand, dielectric resonators and associated metasurfaces can eliminate the issue of ohmic loss while still providing the freedom to engineer the optical properties of the composite. In this talk, I will present our recent efforts to harness this freedom using metasurfaces formed from silicon and fabricated using CMOS-compatible techniques. Operating in the telecommunications band, I will discuss how we have used this platform to realize a number of novel functionalities including wavefront control, near-perfect reflection, and high quality factor resonances. In many cases the optical performance of these silicon-based metasurfaces can surpass their plasmonic counterparts. Furthermore, for some cases the surfaces are more amenable to large-area fabrication techniques.

9. Artificial high birefringence in all-dielectric gradient grating for broadband terahertz waves

PubMed Central

Chen, Meng; Fan, Fei; Xu, Shi-Tong; Chang, Sheng-Jiang

2016-01-01

Subwavelength dielectric gratings are widely applied in the phase and polarization manipulation of light. However, the dispersion of the normal dielectric gratings is not flat while their birefringences are not enough in the THz regime. In this paper, we have fabricated two all-dielectric gratings with gradient grids in the THz regime, of which artificial birefringence is much larger than that of the equal-grid dielectric grating demonstrated by both experiments and simulations. The transmission and dispersion characteristics are also improved since the gradient grids break the periodicity of grating lattices as a chirp feature. From 0.6–1.4 THz, a broadband birefringence reaches 0.35 with a low dispersion and good linearity of phase shift, and the maximum phase shift is 1.4π. Furthermore, these gradient gratings are applied as half-wave plates and realize a linear polarization conversion with a conversion rate over 99%, also much higher than the equal-grid gratings. These gradient gratings show great advantages compared to the periodic gratings and provide a new way in the designing of artificial birefringence material. PMID:27934962

10. Photoconductive ultrafast low gap materials: pulsed THz emitters and detectors

NASA Astrophysics Data System (ADS)

Petrov, Branko; Fekecs, Andre; Chicoine, Martin; Schiettekatte, Francois; Ares, Richard; Morris, Denis

2014-03-01

Commonly photoconductive (PC) switches used for pulsed THz generation and detection are made on GaAs which works at 800 nm. However, there is a need for PC materials compatible with laser sources emitting at 1550 nm since they are of high interest for fiber-coupled devices to be integrated in THz imaging and spectroscopy systems. We have developed such materials based on low bandgap III-V semiconductors. With our novel approach, based on cold-implantation of heavy ions followed by a rapid thermal annealing (RTA) treatment, it was possible to obtain high resistivity (up to 2500 Ω . cm) and short lifetime (<1ps) materials. THz PC antennas were made on these materials and their characteristics were studied by using a THz time-domain spectroscopy (TDS) setup. The impact of the RTA process and different electrode designs were investigated in order to compare the characteristics of PC antennas in terms of amplitude, bandwidth, and signal to noise ratio. For the emitters, bias-voltage and pump-power dependences are shown. Remarkably high electric field (>50 kV/cm) could be applied for increased emission of pulsed THz radiation due to the high resistivity of our materials. Our THz-TDS setup offers measurement capabilities from 0.1 to 3 THz.

11. Design and simulations of CAEP THz FEL resonator

NASA Astrophysics Data System (ADS)

Dou, Yuhuan; Shu, Xiaojian; Deng, Derong; Yang, Xingfan; Li, Ming

2015-02-01

A high power China Academy of Engineering Physics(CAEP) THz free electron laser (FEL) is designed and optimized in a radiation frequency range of 1~3 THz and average output power of about 10 W. The main work focuses on the optimization of different schemes through physical analysis. The wiggler peak field strength and electron beam energy have been selected with eleven frequencies ranging from 1 THz to 3 THz. It is found that the values of the gain and output power of the cavity are largest at 2.6 THz. So we can test the facility at this frequency. While the value of the output power is less than the design goal at the lower frequency region of about 1.0 THz due to the serious slippage between the electron bunch and radiation pulse. To increase the output power at the lower frequency region, the scheme of elliptical hole-coupling optical resonator is proposed to solve this problem. The simulation results show that the elliptical hole-coupling output is effective and applicable for the THz FEL and the output power can be increased by more than 30%.

12. Spiral Antenna-Coupled Microbridge Structures for THz Application.

PubMed

Gou, Jun; Zhang, Tian; Wang, Jun; Jiang, Yadong

2017-12-01

Bolometer sensor is a good candidate for THz imaging due to its compact system, low cost, and wideband operation. Based on infrared microbolometer structures, two kinds of antenna-coupled microbridge structures are proposed with different spiral antennas: spiral antenna on support layer and spiral antenna with extended legs. Aiming at applications in detection and imaging, simulations are carried out mainly for optimized absorption at 2.52 THz, which is the radiation frequency of far-infrared CO2 lasers. The effects of rotation angle, line width, and spacing of the spiral antenna on THz wave absorption of microbridge structures are discussed. Spiral antenna, with extended legs, is a good solution for high absorption rate at low absorption frequency and can be used as electrode lead simultaneously for simplified manufacturing process. A spiral antenna-coupled microbridge structure with an absorption rate of more than 75% at 2.52 THz is achieved by optimizing the structure parameters. This research demonstrates the use of different spiral antennas for enhanced and tunable THz absorption of microbridge structures and provides an effective way to fabricate THz microbolometer detectors with great potential in the application of real-time THz imaging.

13. Reflective terahertz (THz) imaging: system calibration using hydration phantoms

NASA Astrophysics Data System (ADS)

Bajwa, Neha; Garritano, James; Lee, Yoon Kyung; Tewari, Priyamvada; Sung, Shijun; Maccabi, Ashkan; Nowroozi, Bryan; Babakhanian, Meghedi; Sanghvi, Sajan; Singh, Rahul; Grundfest, Warren; Taylor, Zachary

2013-02-01

Terahertz (THz) hydration sensing continues to gain traction in the medical imaging community due to its unparalleled sensitivity to tissue water content. Rapid and accurate detection of fluid shifts following induction of thermal skin burns as well as remote corneal hydration sensing have been previously demonstrated in vivo using reflective, pulsed THz imaging. The hydration contrast sensing capabilities of this technology were recently confirmed in a parallel 7 Tesla Magnetic Resonance (MR) imaging study, in which burn areas are associated with increases in local mobile water content. Successful clinical translation of THz sensing, however, still requires quantitative assessments of system performance measurements, specifically hydration concentration sensitivity, with tissue substitutes. This research aims to calibrate the sensitivity of a novel, reflective THz system to tissue water content through the use of hydration phantoms for quantitative comparisons of THz hydration imagery.Gelatin phantoms were identified as an appropriate tissue-mimicking model for reflective THz applications, and gel composition, comprising mixtures of water and protein, was varied between 83% to 95% hydration, a physiologically relevant range. A comparison of four series of gelatin phantom studies demonstrated a positive linear relationship between THz reflectivity and water concentration, with statistically significant hydration sensitivities (p < .01) ranging between 0.0209 - 0.038% (reflectivity: %hydration). The THz-phantom interaction is simulated with a three-layer model using the Transfer Matrix Method with agreement in hydration trends. Having demonstrated the ability to accurately and noninvasively measure water content in tissue equivalent targets with high sensitivity, reflective THz imaging is explored as a potential tool for early detection and intervention of corneal pathologies.

14. THz-Pulse-Induced Selective Catalytic CO Oxidation on Ru.

PubMed

LaRue, Jerry L; Katayama, Tetsuo; Lindenberg, Aaron; Fisher, Alan S; Öström, Henrik; Nilsson, Anders; Ogasawara, Hirohito

2015-07-17

We demonstrate the use of intense, quasi-half-cycle THz pulses, with an associated electric field component comparable to intramolecular electric fields, to direct the reaction coordinate of a chemical reaction by stimulating the nuclear motions of the reactants. Using a strong electric field from a THz pulse generated via coherent transition radiation from an ultrashort electron bunch, we present evidence that CO oxidation on Ru(0001) is selectively induced, while not promoting the thermally induced CO desorption process. The reaction is initiated by the motion of the O atoms on the surface driven by the electric field component of the THz pulse, rather than thermal heating of the surface.

15. Superconducting Solenoid for Superfast THz Spectroscopy

NASA Astrophysics Data System (ADS)

Bragin, A. V.; Khrushchev, S. V.; Kubarev, V. V.; Mezencev, N. A.; Tsukanov, V. M.; Sozinov, G. I.; Shkaruba, V. A.

This project is related to new spectroscopy method in little-developed THz range. The method is founded on using of a free electron laser (NovoFEL) with high spectral power radiation which can be smoothly tuned in desirable range of spectrum. The objects of research of this method are fast processes in physics, chemical and biological reactions. Uniform magnetic field of 6 T value in the research area can considerably increase possibilities of this method. The magnetic field will modulate radiation of free molecules induction on characteristic frequencies of the Zeeman splitting that gives more possibilities of identification of molecules having even weak magnetic momentum. Moreover, the use of magnetic field allows essentially increase sensitivity of this method due to almost complete separation of weak measuring signals from powerful radiation of the laser. A superconducting solenoid was developed for this method. Its design and peculiarities are described in this paper.

16. Development of SIS Mixers for 1 THz

NASA Technical Reports Server (NTRS)

Zmuidzinas, J.; Kooi, J.; Chattopadhyay, G.; Bumble, B.; LeDuc, H. G.; Stern, J. A.

1998-01-01

SIS heterodyne mixer technology based on niobium tunnel junctions has now been pushed to frequencies over 1 THz, clearly demonstrating that the SIS junctions are capable of mixing at frequencies up to twice the energy gap frequency (4 Delta/h). However, the performance degrades rapidly above the gap frequency of niobium (2 Delta/h approx. 700 GHz) due to substantial ohmic losses in the on-chip tuning circuit. To solve this problem, the tuning circuit should be fabricated using a superconducting film with a larger energy gap, such as NbN; unfortunately, NbN films often have a substantial excess surface resistance in the submillimeter band. In contrast, the SIS mixer measurements we present in this paper indicate that the losses for NbTiN thin films can be quite low.

17. Free-standing THz electromagnetic metamaterials.

PubMed

Moser, H O; Kong, J A; Jian, L K; Chen, H S; Liu, G; Bahou, M; Kalaiselvi, S M P; Maniam, S M; Cheng, X X; Wu, B I; Gu, P D; Chen, A; Heussler, S P; bin Mahmood, Shahrain; Wen, L

2008-09-01

Using micromanufactured S-shaped gold strings suspended in free space by means of window-frames, we experimentally demonstrate an electromagnetic meta-material (EM(3)) in which the metallic structures are no longer embedded in matrices or deposited on substrates such that the response is solely determined by the geometrical parameters and the properties of the metal. Two carefully aligned and assembled window-frames form a bi-layer chip that exhibits 2D left-handed pass-bands corresponding to two different magnetic resonant loops in the range of 1.4 to 2.2 THz as characterized by Fourier transform interferometry and numerical simulation. Chips have a comparably large useful area of 56 mm(2). Our results are a step towards providing EM(3) that fulfill the common notions of a material.

18. Josephson broadband spectroscopy to 1 THz

NASA Astrophysics Data System (ADS)

Edstam, J.; Olsson, H. K.

1994-05-01

We demonstrate the operation of a Josephson Broadband Spectrometer'' (JOBS) with a frequency range and bandwidth of 1 THz. The JOBS uses the inherent frequency tuning of the Josephson oscillations (f=2 eV/h) as a probe of the complex impedance environment, ZL(f), of the Josephson junction. Spectra taken of microstrip resonators (YBa2Cu3O7/SiO/Au) display up to nine harmonic resonances corresponding to a bandwidth of 1000 GHz. We find the surface resistance of YBa2Cu3O7 to scale as f2 over this frequency range, whereas the London penetration depth is frequency independent. The upper frequency limit of the measurement is set by the resonator loss whereas the JOBS presumably has an even larger intrinsic bandwidth.

19. Perspective: Ultrafast magnetism and THz spintronics

NASA Astrophysics Data System (ADS)

Walowski, Jakob; Münzenberg, Markus

2016-10-01

This year the discovery of femtosecond demagnetization by laser pulses is 20 years old. For the first time, this milestone work by Bigot and coworkers gave insight directly into the time scales of microscopic interactions that connect the spin and electron system. While intense discussions in the field were fueled by the complexity of the processes in the past, it now became evident that it is a puzzle of many different parts. Rather than providing an overview that has been presented in previous reviews on ultrafast processes in ferromagnets, this perspective will show that with our current depth of knowledge the first applications are developed: THz spintronics and all-optical spin manipulation are becoming more and more feasible. The aim of this perspective is to point out where we can connect the different puzzle pieces of understanding gathered over 20 years to develop novel applications. Based on many observations in a large number of experiments. Differences in the theoretical models arise from the localized and delocalized nature of ferromagnetism. Transport effects are intrinsically non-local in spintronic devices and at interfaces. We review the need for multiscale modeling to address the processes starting from electronic excitation of the spin system on the picometer length scale and sub-femtosecond time scale, to spin wave generation, and towards the modeling of ultrafast phase transitions that altogether determine the response time of the ferromagnetic system. Today, our current understanding gives rise to the first usage of ultrafast spin physics for ultrafast magnetism control: THz spintronic devices. This makes the field of ultrafast spin-dynamics an emerging topic open for many researchers right now.

20. Room temperature strong light-matter coupling in 3D THz meta-atoms (Conference Presentation)

NASA Astrophysics Data System (ADS)

Paulillo, Bruno; Manceau, Jean-Michel; Li, Lianhe; Linfield, Edmund; Colombelli, Raffaele

2016-04-01

We demonstrate strong light-matter coupling at room temperature in the terahertz (THz) spectral region using 3D meta-atoms with extremely sub-wavelength volumes. Using an air-bridge fabrication scheme, we have implemented sub-wavelength 3D THz micro-resonators that rely on suspended loop antennas connected to semiconductor-filled patch cavities. We have experimentally shown that they possess the functionalities of lumped LC resonators: their frequency response can be adjusted by independently tuning the inductance associated the antenna element or the capacitance provided by the metal-semiconductor-metal cavity. Moreover, the radiation coupling and efficiency can be engineered acting on the design of the loop antenna, similarly to conventional RF antennas. Here we take advantage of this rich playground in the context of cavity electrodynamics/intersubband polaritonics. In the strong light-matter coupling regime, a cavity and a two-level system exchange energy coherently at a characteristic rate called the vacuum Rabi frequency ΩR which is dominant with respect to all other loss mechanisms involved. The signature, in the frequency domain, is the appearance of a splitting between the bare cavity and material system resonances: the new states are called upper and a lower polariton branches. So far, most experimental demonstrations of strong light-matter interaction between an intersubband transition and a deeply sub-wavelength mode in the THz or mid-infrared ranges rely on wavelength-scale or larger resonators such as photonic crystals, diffractive gratings, dielectric micro-cavities or patch cavities. Lately, planar metamaterials have been used to enhance the light-matter interaction and strongly reduce the interaction volume by engineering the electric and magnetic resonances of the individual subwavelength constituents. In this contribution we provide evidence of strong coupling between a THz intersubband transition and an extremely sub-wavelength mode (≈λ/10

1. Comparison of Thermal Detector Arrays for Off-Axis THz Holography and Real-Time THz Imaging.

PubMed

Hack, Erwin; Valzania, Lorenzo; Gäumann, Gregory; Shalaby, Mostafa; Hauri, Christoph P; Zolliker, Peter

2016-02-06

In terahertz (THz) materials science, imaging by scanning prevails when low power THz sources are used. However, the application of array detectors operating with high power THz sources is increasingly reported. We compare the imaging properties of four different array detectors that are able to record THz radiation directly. Two micro-bolometer arrays are designed for infrared imaging in the 8-14 μm wavelength range, but are based on different absorber materials (i) vanadium oxide; (ii) amorphous silicon; (iii) a micro-bolometer array optimized for recording THz radiation based on silicon nitride; and (iv) a pyroelectric array detector for THz beam profile measurements. THz wavelengths of 96.5 μm, 118.8 μm, and 393.6 μm from a powerful far infrared laser were used to assess the technical performance in terms of signal to noise ratio, detector response and detectivity. The usefulness of the detectors for beam profiling and digital holography is assessed. Finally, the potential and limitation for real-time digital holography are discussed.

2. Comparison of Thermal Detector Arrays for Off-Axis THz Holography and Real-Time THz Imaging

PubMed Central

Hack, Erwin; Valzania, Lorenzo; Gäumann, Gregory; Shalaby, Mostafa; Hauri, Christoph P.; Zolliker, Peter

2016-01-01

In terahertz (THz) materials science, imaging by scanning prevails when low power THz sources are used. However, the application of array detectors operating with high power THz sources is increasingly reported. We compare the imaging properties of four different array detectors that are able to record THz radiation directly. Two micro-bolometer arrays are designed for infrared imaging in the 8–14 μm wavelength range, but are based on different absorber materials (i) vanadium oxide; (ii) amorphous silicon; (iii) a micro-bolometer array optimized for recording THz radiation based on silicon nitride; and (iv) a pyroelectric array detector for THz beam profile measurements. THz wavelengths of 96.5 μm, 118.8 μm, and 393.6 μm from a powerful far infrared laser were used to assess the technical performance in terms of signal to noise ratio, detector response and detectivity. The usefulness of the detectors for beam profiling and digital holography is assessed. Finally, the potential and limitation for real-time digital holography are discussed. PMID:26861341

3. High power THz sources and applications at ENEA-Frascati

NASA Astrophysics Data System (ADS)

Gallerano, G. P.; Doria, A.; Giovenale, E.; Spassovsky, I.

2014-01-01

ENEA has a long term expertise in the development of powerful short-pulse mm-wave and THz radiation sources driven by free electrons. Various electron-wave interaction schemes were successfully tested in the past, including Cerenkov and Smith-Purcell radiators as well as undulator devices. Two THz-FEL sources are currently available, covering altogether the spectral range from 90 GHz to 0.7 THz. Recently a novel Electro-Magnetic pulser, capable of providing both nanosecond THz electromagnetic (EM) radiation pulses and electrostatic (ES) pulses with identical time duration in one device has been designed and is currently under development. The pulser will allow, for the first time, direct comparison of EM and ES pulses on biological systems with peak electric fields that are significantly higher than any reported to date.

4. THz-wave parametric sources and imaging applications

NASA Astrophysics Data System (ADS)

Kawase, Kodo

2004-12-01

We have studied the generation of terahertz (THz) waves by optical parametric processes based on laser light scattering from the polariton mode of nonlinear crystals. Using parametric oscillation of MgO-doped LiNbO3 crystal pumped by a nano-second Q-switched Nd:YAG laser, we have realized a widely tunable coherent THz-wave sources with a simple configuration. We have also developed a novel basic technology for THz imaging, which allows detection and identification of chemicals by introducing the component spatial pattern analysis. The spatial distributions of the chemicals were obtained from terahertz multispectral trasillumination images, using absorption spectra previously measured with a widely tunable THz-wave parametric oscillator. Further we have applied this technique to the detection and identification of illicit drugs concealed in envelopes. The samples we used were methamphetamine and MDMA, two of the most widely consumed illegal drugs in Japan, and aspirin as a reference.

5. SUB-THz RADIATION MECHANISMS IN SOLAR FLARES

SciTech Connect

Fleishman, Gregory D.; Kontar, Eduard P.

2010-02-01

Observations in the sub-THz range of large solar flares have revealed a mysterious spectral component increasing with frequency and hence distinct from the microwave component commonly accepted to be produced by gyrosynchrotron (GS) emission from accelerated electrons. Evidently, having a distinct sub-THz component requires either a distinct emission mechanism (compared to the GS one), or different properties of electrons and location, or both. We find, however, that the list of possible emission mechanisms is incomplete. This Letter proposes a more complete list of emission mechanisms, capable of producing a sub-THz component, both well known and new in this context, and calculates a representative set of their spectra produced by (1) free-free emission, (2) GS emission, (3) synchrotron emission from relativistic positrons/electrons, (4) diffusive radiation, and (5) Cherenkov emission. We discuss the possible role of the mechanisms in forming the sub-THz emission and emphasize their diagnostics potential for flares.

6. The Jefferson Lab High Power THz User Facility

SciTech Connect

John Klopf; Amelia Greer; Joseph Gubeli; George Neil; Michelle D. Shinn; Timothy Siggins; David W. Waldman; Gwyn Williams; Alan Todd; Vincent Christina; Oleg Chubar

2007-04-27

We describe here, a high power (100 Watt average, 10 MW peak) broadband THz facility based on emission from sub-picosecond bunches of relativistic electrons and the beam transport system that delivers this beam in to a user laboratory.

7. Tunable THz perfect absorber using graphene-based metamaterials

NASA Astrophysics Data System (ADS)

Faraji, Mahboobeh; Moravvej-Farshi, Mohammad Kazem; Yousefi, Leila

2015-11-01

A tunable THz absorber, with absorbance more than 90% is proposed, and numerically characterized. The absorber structure is based on metamaterials with unit cells consisting of two patterned graphene layers separated by a 5-nm thick layer of Al2O3. Numerical results show that when the chemical potential of the top graphene microribbons are tuned by an external variable bias and that of the lower graphene fishnet is kept at μC=0, frequency of the absorption peaks can be tuned as desired, therefore we can have a tunable or switchable absorber. The proposed absorber can have applications in designing tunable reflective THz filters or tunable THz switches and modulators. It can also be used for cloaking objects in THz range.

8. High precision spectroscopy and imaging in THz frequency range

NASA Astrophysics Data System (ADS)

Vaks, Vladimir L.

2014-03-01

Application of microwave methods for development of the THz frequency range has resulted in elaboration of high precision THz spectrometers based on nonstationary effects. The spectrometers characteristics (spectral resolution and sensitivity) meet the requirements for high precision analysis. The gas analyzers, based on the high precision spectrometers, have been successfully applied for analytical investigations of gas impurities in high pure substances. These investigations can be carried out both in absorption cell and in reactor. The devices can be used for ecological monitoring, detecting the components of chemical weapons and explosive in the atmosphere. The great field of THz investigations is the medicine application. Using the THz spectrometers developed one can detect markers for some diseases in exhaled air.

9. Calculations for Tera-Hertz (THZ) Radiation Sources

SciTech Connect

Hussein, Yasser A.; Spencer, James E.; /SLAC

2005-06-07

We explore possibilities for THz sources from 0.3-30 THz. While still inaccessible, this broad gap is even wider for advanced acceleration schemes extending from X or, at most, W band RF at the low end up to CO{sub 2} lasers. While the physical implementations of these two approaches are quite different, both are proving difficult to develop so that lower frequency, superconducting RF is currently preferred. Similarly, the validity of modeling techniques varies greatly over this range of frequencies but generally mandates coupling Maxwell's equations to the appropriate device transport physics for which there are many options. Here we study radiation from undulatory-shaped transmission lines using finite-difference, time-domain (FDTD) simulations. Also, we present Monte-Carlo techniques for pulse generation. Examples of THz sources demonstrating coherence are shown with the goal of optimizing on-chip THz radiators for applications that may lead to accelerators.

10. FLUTE: a versatile linac-based THz source.

PubMed

Nasse, M J; Schuh, M; Naknaimueang, S; Schwarz, M; Plech, A; Mathis, Y-L; Rossmanith, R; Wesolowski, P; Huttel, E; Schmelling, M; Müller, A-S

2013-02-01

A new compact versatile linear accelerator named FLUTE is currently being designed at the Karlsruhe Institute of Technology. This paper presents the status of this 42 MeV machine. It will be used to generate strong (several 100 MV/m) ultra-short (~1 ps) THz pulses (up to ~4-25 THz) for photon science experiments, as well as to conduct a variety of accelerator studies. The latter range from comparing different coherent THz radiation generation schemes to compressing electron bunches and studying the electron beam stability. The bunch charge will cover a wide range (~100 pC-3 nC). Later we plan to also produce ultra-short x-ray pulses from the electron bunches, which, for example, could then be combined for THz pump-x-ray probe experiments.

11. FLUTE: A versatile linac-based THz source

SciTech Connect

Nasse, M. J.; Schuh, M.; Schwarz, M.; Naknaimueang, S.; Mathis, Y.-L.; Rossmanith, R.; Wesolowski, P.; Huttel, E.; Plech, A.; Schmelling, M.; Mueller, A.-S.

2013-02-15

A new compact versatile linear accelerator named FLUTE is currently being designed at the Karlsruhe Institute of Technology. This paper presents the status of this 42 MeV machine. It will be used to generate strong (several 100 MV/m) ultra-short ({approx}1 ps) THz pulses (up to {approx}4-25 THz) for photon science experiments, as well as to conduct a variety of accelerator studies. The latter range from comparing different coherent THz radiation generation schemes to compressing electron bunches and studying the electron beam stability. The bunch charge will cover a wide range ({approx}100 pC-3 nC). Later we plan to also produce ultra-short x-ray pulses from the electron bunches, which, for example, could then be combined for THz pump-x-ray probe experiments.

12. THz QCL self-mixing interferometry for biomedical applications

NASA Astrophysics Data System (ADS)

Rakić, Aleksandar D.; Taimre, Thomas; Bertling, Karl; Lim, Yah Leng; Wilson, Stephen J.; Nikolić, Milan; Valavanis, Alexander; Indjin, Dragan; Linfield, Edmund H.; Davies, A. Giles; Ferguson, Blake; Walker, Graeme; Schaider, Helmut; Soyer, H. Peter

2014-09-01

In this paper, we introduce the self-mixing phenomenon in terahertz quantum cascade lasers (THz QCLs) and present recent advancements in the development of coherent THz imaging and sensing systems that exploit the self-mixing effect. We describe an imaging method which utilises the interferometric nature of optical feedback in a THz QCL to employ it as a homodyning transceiver. This results in a highly sensitive and compact scheme. Due to the inherently low penetration depth of THz radiation in hydrated biological tissue, imaging of superficial skin is an ideal application for this technique. We present results for imaging of excised skin tissue, showing high-contrast between different tissue types and pathologies.

13. THz time-domain spectroscopy imaging for mail inspection

NASA Astrophysics Data System (ADS)

Zhang, Liquan; Wang, Zhongdong; Ma, Yanmei; Hao, Erjuan

2011-08-01

Acquiring messages from the mail but not destroying the envelope is a big challenge in the war of intelligence. If one can read the message of the mail when the envelope is closed, he will benefit from the message asymmetry and be on a good wicket in the competition. In this paper, we presented a transmitted imaging system using THz time-domain spectroscopy technology. We applied the system to image the mail inside an envelope by step-scanning imaging technology. The experimental results show that the THz spectroscopy can image the mail in an envelope. The words in the paper can be identified easily from the background. We also present the THz image of a metal blade in the envelope, in which we can see the metal blade clearly. The results show that it is feasible of THz Time-Domain Spectroscopy Imaging for mail inspection applications.

14. Dielectric Metamaterials with Toroidal Dipolar Response

NASA Astrophysics Data System (ADS)

Basharin, Alexey A.; Kafesaki, Maria; Economou, Eleftherios N.; Soukoulis, Costas M.; Fedotov, Vassili A.; Savinov, Vassili; Zheludev, Nikolay I.

2015-01-01

Toroidal multipoles are the terms missing in the standard multipole expansion; they are usually overlooked due to their relatively weak coupling to the electromagnetic fields. Here, we propose and theoretically study all-dielectric metamaterials of a special class that represent a simple electromagnetic system supporting toroidal dipolar excitations in the THz part of the spectrum. We show that resonant transmission and reflection of such metamaterials is dominated by toroidal dipole scattering, the neglect of which would result in a misunderstanding interpretation of the metamaterials' macroscopic response. Because of the unique field configuration of the toroidal mode, the proposed metamaterials could serve as a platform for sensing or enhancement of light absorption and optical nonlinearities.

15. Analysis of cavity and window for THz gyrotron

SciTech Connect

Alaria, Mukesh Kumar; Mukherjee, P.; Rao, R.R.; Sinha, A.K. E-mail: aksinha@ceeri.ernet.in

2011-07-01

In this paper study of cavity and window has been carried out using Ansoft HFSS for Terahertz Gyrotron. Eigen mode analysis of the cavity has been carried out at 1 THz. An idea about the operating modes in the cavity of the Gyrotron and obtained the simulated Eigen frequency and field pattern of the modes. The design of window for 1 THz Gyrotron has also been carried out using HFSS. The simulated results have also been compared with ST microwave studio. (author)

16. The physical theory and propagation model of THz atmospheric propagation

NASA Astrophysics Data System (ADS)

Wang, R.; Yao, J. Q.; Xu, D. G.; Wang, J. L.; Wang, P.

2011-02-01

Terahertz (THz) radiation is extensively applied in diverse fields, such as space communication, Earth environment observation, atmosphere science, remote sensing and so on. And the research on propagation features of THz wave in the atmosphere becomes more and more important. This paper firstly illuminates the advantages and outlook of THz in space technology. Then it introduces the theoretical framework of THz atmospheric propagation, including some fundamental physical concepts and processes. The attenuation effect (especially the absorption of water vapor), the scattering of aerosol particles and the effect of turbulent flow mainly influence THz atmosphere propagation. Fundamental physical laws are illuminated as well, such as Lamber-beer law, Mie scattering theory and radiative transfer equation. The last part comprises the demonstration and comparison of THz atmosphere propagation models like Moliere(V5), SARTre and AMATERASU. The essential problems are the deep analysis of physical mechanism of this process, the construction of atmospheric propagation model and databases of every kind of material in the atmosphere, and the standardization of measurement procedures.

17. Investigation on 2.45-THz array transmission imaging

NASA Astrophysics Data System (ADS)

Yao, Rui; Li, Qi; Ding, Shenghui; Wang, Qi

2009-07-01

THz transmission imaging is considered as a promising detection measure and imaging method with wide application prospect in security inspection and counter-terrorism. And high-speed array imaging is a very important direction. In this paper, 2.45-THz transmission imaging experiments are made by applying a 124×124 array detector. The 2.45-THz CW CO2-pumped laser is used as illumination source and its output power is about 17mW. Some undersize articles (gasket, screw and nut) are chosen as objects. THz imaging experiments are respectively demonstrated through 1-2 pieces of paper and two kinds of envelopes to show the imaging effect. The original data is acquired and some image processing methods (5-frame average, median filtering, etc) are used to improve the image effect. Finally the THz images obtained are basically clear. The experimental results show that utilizing the setup designed for 2.45-THz imaging, the images are fast generated and objects' contours are clear through paper and envelop.

18. Computational Investigations of THz Transmittance in the Atmosphere

NASA Astrophysics Data System (ADS)

Yang, Xingyu; Calhoun, Casey; Calhoun, Ronald

2016-06-01

With the recent scientific advancements in Terahertz (THz) wave propagation and reception technology, there has been significant development in new possibilities for using THz waves - offering new possibilities in THz detection and ranging. A first foundational step toward this goal is to better understand THz transmittance in the turbulent atmosphere. In this project, a frequency modulation pattern of THz waves was created by utilizing a system of shifting frequency based on temperature, air humidity, and distance of transmission. The total path loss of the wave in air, based on the wave spread and molecular absorption, was then modeled using radiative transfer theory, onto a set of JavaHAWK filtered-HITRAN data representative of an air sample. This data was used to generate a path loss matrix, which was then used to optimize frequency of transmission for the specific conditions. The concept to be evaluated is whether adaptive frequency modulated THz might usefully decrease transmission losses by adjusting to atmospheric conditions (such as local variations in temperature and humidity).

19. Non-Destructive Evaluation (NDE) Applications of THz Radiation

NASA Astrophysics Data System (ADS)

Zimdars, David

2005-03-01

The technology and applications of time domain terahertz (THz) imaging to non-destructive evaluation (NDE) will be discussed. THz imaging has shown great promise in 2 and 3 dimensional non-contact inspection of non-conductive materials such as plastics, foam, composites, ceramics, paper, wood and glass. THz imaging employs safe low power non-ionizing electromagnetic pulses, with lateral resolution < 200 um, and depth resolution < 50 um. THz pulses can be analyzed spectroscopically to reveal chemical content. Recently, highly integrated turn-key THz imaging systems have been introduced commercially. We will demonstrate the detection of voids and disbonds intentionally incorporated within the sprayed on foam insulation of a space shuttle external tank mock-up segments. An industrially hardened THz scanning system which has been deployed to scan the space shuttle tank with small remote transceiver will be described. Additional terahertz security imaging applications for the detection of weapons and explosives will also be discussed, as well as the application of terahertz sensors for high speed industrial process monitoring and quality control.

20. Co-integrated microfluidic and THz functions for biochip devices

NASA Astrophysics Data System (ADS)

Laurette, S.; Treizebre, A.; Bocquet, B.

2011-06-01

TeraHertz (THz) spectroscopy is becoming an alternative way to probe biological interactions in real-time conditions. However, accurate and reproducible THz measurements of aqueous solutions, largely represented in life sciences, remain difficult. A THz microsystem which couples both electromagnetic and microfluidic integrated functions is presented here. Its technological process is accurately detailed and enables easy designs of advanced THz and microfluidic functions. It is composed of the deposition of gold wires on a glass wafer to guide the THz waves. Then, a whole silicon wafer is bonded by using a thermosensitive-polymer thermo-compression. Silicon is deep-etched to create the microchannels which are finally covered with a second glass wafer. This bonding-etching process enables huge freedom and independence for electromagnetic and microfluidic designs. The technological process characterization has shown that the manufactured biochip is compatible with pressures up to 37 bar. First measurements with empty and water-filled channels have been carried out and have shown the ability to perform THz spectroscopy inside the chip. Then, first measurements on proteins have been performed and shown the system ability to probe protein concentration. This kind of microfluidic microsystem, allowing complex design for integrated electronic and microfluidic circuits, defines a true new instrumental way for life science investigations.

1. Chiral THz metamaterial with tunable optical activity

SciTech Connect

Zhou, Jiangfeng; Taylor, Antoinette; O' Hara, John; Chowdhury, Roy; Zhao, Rongkuo; Soukoullis, Costas M

2010-01-01

Optical activity in chiral metamaterials is demonstrated in simulation and shows actively tunable giant polarization rotation at THz frequencies. Electric current distributions show that pure chirality is achieved by our bi-Iayer chiral metamaterial design. The chirality can be optically controlled by illumination with near-infrared light. Optical activity, occurring in chiral materials such as DNA, sugar and many other bio-molecules, is a phenomenon of great importance to many areas of science including molecular biology, analytical chemistry, optoelectronics and display applications. This phenomenon is well understood at an effective medium level as a magnetic/electric moment excited by the electric/magnetic field of the incident electromagnetic (EM) wave. Usually, natural chiral materials exhibit very weak optical activity e.g. a gyrotropic quartz crystal. The optical activity of chiral metamaterials, however, can be five orders of magnitude stronger. Chiral metamaterials are made of sub-wavelength resonators lacking symmetry planes. The asymmetry allows magnetic moments to be excited by the electric field of the incident EM wave and vice versa. Recently, chiral metamaterials have been demonstrated and lead to prospects in giant optical activity, circular dichroism, negative refraction and reversing the Casmir force. These fascinating optical properties require strong chirality, which may be designed through the microscopic structure of chiral metamaterials. However, these metamaterials have a fixed response function, defined by the geometric structuring, which limits their ability to manipulate EM waves. Active metamaterials realize dynamic control of response functions and have produced many influential applications such as ultra-fast switching devices, frequency and phase modulation and memory devices. Introducing active designs to chiral metamaterials will give additional freedom in controlling the optical activity, and therefore enable dynamic manipulation

2. Mid-IR to THz polaritonics: realizing novel materials for nanophotonics (Conference Presentation)

NASA Astrophysics Data System (ADS)

Caldwell, Joshua D.

2016-09-01

The field of nanophotonics is based on the ability to confine light to sub-diffractional dimensions. Up until recently, research in this field has been primarily focused on the use of plasmonic metals. However, the high optical losses inherent in such metal-based surface plasmon materials has led to an ever-expanding effort to identify, low-loss alternative materials capable of supporting sub-diffractional confinement. Beyond this, the limited availability of high efficiency optical sources, refractive and compact optics in the mid-infrared to THz spectral regions make nanophotonic advancements imperative. One highly promising alternative are polar dielectric crystals whereby sub-diffraction confinement of light can be achieved through the stimulation of surface phonon polaritons within an all-dielectric, and thus low loss material system. Due to the wide array of high quality crystalline species and varied crystal structures, a wealth of unanticipated optical properties have recently been reported. However, these materials also have some limitations, primarily in the limited spectral bandwidth of operation for any given material. This talk will discuss recent advancements to improve the material lifetime and to induce additional functionality through isotopic enrichment and hybridization of polaritonic modes for realizing low-loss, actively tunable/modulated nanophotonic materials.

3. Generation of efficient THz radiation by optical rectification in DAST crystal using tunable femtosecond laser pulses

NASA Astrophysics Data System (ADS)

Venkatesh, Mottamchetty; Thirupugalmani, K.; Rao, K. S.; Brahadeeswaran, S.; Chaudhary, A. K.

2017-03-01

We report the efficient THz generation by optical rectification from an indigenously grown organic DAST crystal using the 140 fs oscillator laser pulses tunable in between 780 and 850 nm. The generated THz pulse profile and powers have been measured using the photoconductive (PC) antennas and pyroelectric detector, respectively. The highest THz peak amplitude and power is obtained at 825 nm central wavelength. We have theoretically explained the enhancement of THz radiation based on the matching of average optical group refractive index and average THz refractive index of the DAST crystal at 825 nm. In addition, the dependence of THz peak amplitude and THz power on laser power have been carried out. The measured quantum conversion efficiency (QCE) of 0.5 and 1.5 THz bands are of the order 3.7 × 10-3, 1.4 × 10-3, respectively. Finally, an attempt has been made to study the effect of polarizations on generated THz signal.

4. Intense THz radiation produced in organic salt crystals for high-field applications

NASA Astrophysics Data System (ADS)

Vicario, C.; Ruchert, C.; Hauri, C. P.

2013-03-01

Organic stilbazolium salt crystals pumped by intense, ultrashort mid-infrared laser have been investigated for efficient THz generation by optical rectification. In this paper we present our latest results in view of the generation of single-cycle and high-field THz transient in the THz gap (0.1-10 THz). The organic rectifiers like DAST, OH1 and DSTMS combine extremely large optical susceptibility with excellent velocity matching between the infrared pump and the THz radiation. Our simple collinear conversion scheme provides THz beams with excellent focusing properties and single cycle electric field larger than 1.5 MV/cm and magnetic field strength beyond 0.5 Tesla. The source can potentially cover the full THz gap at field strength which is barely provided by other THz sources. The THz pulse is carrier-envelope phase stable and the polarity of the field can be easily inverted.

5. PECVD of low-dielectric constant films for ULSI

NASA Astrophysics Data System (ADS)

Shimogaki, Yukihiro

1998-10-01

We studied the reduction mechanism of the dielectric constant of F-doped silicon oxide films prepared by PECVD from SiH_4/N_2O/CF4 mixture. From the estimation of the dielectric constant at various frequencies, ranging from 1MHz to 100THz, using CV measurement, Kramers-Kronig relation and the square of the refractive index, we suggest that the dielectric constant due to ionic and electronic polarization is not the dominant factor in decreasing the dielectric constant. It is important to remove -OH in films to obtain very low dielectric constant F-doped silicon oxide films, because Si-OH is the main factor of the orientational polarization in silicon oxide films made by PECVD. To investigate the reaction mechanism which controls the film structure, we changed the residence time of gas in chamber by varying the flow rate. When the residence time in chamber decreases, the film deposition rate increases. We tried to explain flow rate dependency of the deposition rate using a simple CSTR (continuous stirred tank reactor) model. It can be concluded that there are two paths to deposit the films. One route is a deposition by the precursors with poor step coverage profile, and the other route is deposition through intermediates formed by gas phase reactions that contribute to have better step coverage. The overall gas phase reaction rate constant was estimated from these kinetic studies. Same approach was also carried out on the PECVD of C:F film deposition.

6. Dielectric Susceptibility of Liquid Water: Microscopic Insights from Coherent and Incoherent Neutron Scattering

NASA Astrophysics Data System (ADS)

Arbe, A.; Malo de Molina, P.; Alvarez, F.; Frick, B.; Colmenero, J.

2016-10-01

The analysis of neutron scattering results on H dynamics (H2O ) and the dynamic structure factor (D2O ) around the intermolecular peak and at intermediate length scales in terms of the susceptibilities reveals three processes (diffusive, local relaxational and vibrational) at frequencies below 3 THz, to which the contributions commonly invoked in dielectric studies can be directly mapped. We achieve a unified description of the results from both techniques, clarifying the nature of the molecular motions involved in the dielectric spectra and their impact on the structural relaxation.

7. THz Spectroscopy and Spectroscopic Database for Astrophysics

NASA Technical Reports Server (NTRS)

Pearson, John C.; Drouin, Brian J.

2006-01-01

Molecule specific astronomical observations rely on precisely determined laboratory molecular data for interpretation. The Herschel Heterodyne Instrument for Far Infrared, a suite of SOFIA instruments, and ALMA are each well placed to expose the limitations of available molecular physics data and spectral line catalogs. Herschel and SOFIA will observe in high spectral resolution over the entire far infrared range. Accurate data to previously unimagined frequencies including infrared ro-vibrational and ro-torsional bands will be required for interpretation of the observations. Planned ALMA observations with a very small beam will reveal weaker emission features requiring accurate knowledge of higher quantum numbers and additional vibrational states. Historically, laboratory spectroscopy has been at the front of submillimeter technology development, but now astronomical receivers have an enormous capability advantage. Additionally, rotational spectroscopy is a relatively mature field attracting little interest from students and funding agencies. Molecular data base maintenance is tedious and difficult to justify as research. This severely limits funding opportunities even though data bases require the same level of expertise as research. We report the application of some relatively new receiver technology into a simple solid state THz spectrometer that has the performance required to collect the laboratory data required by astronomical observations. Further detail on the lack of preparation for upcoming missions by the JPL spectral line catalog is given.

8. Grating THz laser with optical pumping

NASA Astrophysics Data System (ADS)

Khoury, Jed; Haji-saeed, Bahareh; Woods, Charles; Kierstead, John

2010-04-01

In this paper, we present a design for a widely tunable solid-state optically and electrically pumped THz laser based on the Smith-Purcell free-electron laser. In the free-electron laser, an energetic electron beam pumps a metallic grating to generate surface plasmons. Our solid-state optically pumped design consists of a thin layer of dielectic, such as SiNx, sandwiched between a corrugated structure and a thin metal or semiconductor layer. The lower layer is for current streaming, and replaces the electron beam in the original design. The upper layer consists of one micro-grating for coupling the electromagnetic field in, another for coupling out, and a nano-grating for coupling with the current in the lower layer for electromagnetic field generation. The surface plasmon waves generated from the upper layer by an external electromagnetic field, and the lower layer by the applied current, are coupled. Emission enhancement occurs when the plasmonic waves in both layers are resonantly coupled.

9. The Kassel Laboratory Astrophysics Thz Spectrometrs

NASA Astrophysics Data System (ADS)

Chantzos, Johanna; Herberth, Doris; Kutzer, Pia; Muster, Christoph; Fuchs, Guido W.; Giesen, Thomas

2016-06-01

We present a brief overview of the recently established laboratory astrophysics group in Kassel/Germany with a focus on our THz technology. After an outline of our laboratory equipment and recent projects the talk will focus on our new fast spectral scan technique for molecular jet experiments. Here, a new test setup for broadband fast sweep spectrometry in the MW to submm wavelength region has been realized and can be applied to identify transient molecules in a supersonic jet. An arbitrary waveform generator (AWG) is used to generate chirped pulses with a linear frequency sweep in the MHz regime. Pulse durations are of a few microseconds. These pulses are up-converted in frequency, e.g. into the 50 GHz microwave frequency range utilizing a synthesizer, or using a synthesizer plus standard amplifier multiplier chain (AMC) to reach the 100-300 GHz region. As test, NH_3 has been measured between 18-26 GHz in a supersonic jet of 500 μ s duration. Acetonitrile (CH_3CN) was tested in the (90-110) GHz range. The spectrometer is capable of providing fast, broadband and low-noise measurements. Experiments with non-stabel molecular production conditions can greatly benefit from these advantages. The setup enables the study of Van-der-Waals-clusters, as well as carbon chain molecules and small metal-containing refractory molecules when combined with appropriate molecule sources.

10. Intrinsic dielectric properties of magnetodielectric La2CoMnO6

NASA Astrophysics Data System (ADS)

Silva, R. X.; Moreira, R. L.; Almeida, R. M.; Paniago, R.; Paschoal, C. W. A.

2015-06-01

Manganite with a double perovskite structure is an attractive material because of its interesting magnetoelectric and dielectric responses. In particular, colossal dielectric constant (CDC) behavior has been observed in La2CoMnO6 (LCMO) at radio frequencies and at room temperature. In this paper, we used infrared-reflectivity spectroscopy to study a LCMO ceramic obtained through a modified Pechini's method to determine the phonon contribution to the intrinsic dielectric response of the system and to investigate the CDC origin. The analysis of the main polar modes and of the obtained phonon parameters indicate that the CDC effect of LCMO is of pure extrinsic origin. In addition, we estimated the dielectric constant and the quality factor of the material in the microwave region to be ɛ's ˜ 16 and Qu × f ˜ 124 THz, which verifies that LCMO is appropriate for application in microwave devices and circuitry.

11. Dielectric response of wurtzite gallium nitride in the terahertz frequency range

NASA Astrophysics Data System (ADS)

Hibberd, M. T.; Frey, V.; Spencer, B. F.; Mitchell, P. W.; Dawson, P.; Kappers, M. J.; Oliver, R. A.; Humphreys, C. J.; Graham, D. M.

2016-12-01

We report on the characterization of the intrinsic, anisotropic, dielectric properties of wurtzite gallium nitride in the spectral range of 0.5-11 THz, using terahertz time-domain spectroscopy. The ordinary (ε˜⊥) and extraordinary (ε˜∥) components of the complex dielectric function were determined experimentally for a semi-insulating, m-plane gallium nitride single crystal, providing measurements of the refractive indices (n⊥,∥) and absorption coefficients (α⊥,∥) . These material parameters were successfully modeled by considering the contribution of the optical phonon modes, measured using Raman spectroscopy, to the dielectric function, giving values for the relative static dielectric constants of ε0⊥ = 9.22 ± 0.02 and ε0∥ = 10.32 ± 0.03 for wurtzite gallium nitride.

12. THz-Raman spectroscopy for explosives, chemical, and biological detection

NASA Astrophysics Data System (ADS)

Carriere, James T. A.; Havermeyer, Frank; Heyler, Randy A.

2013-05-01

Raman and Terahertz spectroscopy are both widely used for their ability to safely and remotely identify unknown materials. Each approach has its advantages and disadvantages. Traditional Raman spectroscopy typically measures molecular energy transitions in the 200-5000cm-1 region corresponding to sub-molecular stretching or bending transitions, while Terahertz spectroscopy measures molecular energy transitions in the 1-200cm-1 region (30GHz - 6THz) that correspond to low energy rotational modes or vibrational modes of the entire molecule. Many difficult to detect explosives and other hazardous chemicals are known to have multiple relatively strong transitions in this "Terahertz" (<200cm-1, <6THz) regime, suggesting this method as a powerful complementary approach for identification. However, THz signal generation is often expensive, many THz spectroscopy systems are limited to just a few THz range, and strong water absorption bands in this region can act to mask certain transitions if great care isn't taken during sample preparation. Alternatively, low-frequency or "THz-Raman" spectroscopy, which covers the ~5cm-1 to 200cm-1 (150GHz - 6 THz) regions and beyond, offers a powerful, compact and economical alternative to probe these low energy transitions. We present results from a new approach for extending the range of Raman spectroscopy into the Terahertz regime using an ultra-narrow-band volume holographic grating (VHG) based notch filter system. An integrated, compact Raman system is demonstrated utilizing a single stage spectrometer to show both Stokes and anti-Stokes measurements down to <10cm-1 on traditionally difficult to detect explosives, as well as other chemical and biological samples.

13. Strong terahertz absorption in all-dielectric Huygens' metasurfaces.

PubMed

Cole, Michael A; Powell, David A; Shadrivov, Ilya V

2016-09-19

We propose an all dielectric metamaterial that acts as a perfect terahertz absorber without a ground plane. The unit cell consists of a dielectric cylinder embedded in a low index material. In order to achieve near-perfect terahertz absorption (99.5%) we employ impedance matching of the electric and magnetic resonances within the cylinders of the Huygens' metasurface. The impedance matching is controlled by changing the aspect ratio between the height and diameter of the cylinder. We show that the absorption resonance can be tuned to particular frequencies from 0.3 to 1.9 THz via changing the geometry of the structure while keeping a nearly constant aspect ratio of the cylinders.

14. Strong terahertz absorption in all-dielectric Huygens’ metasurfaces

NASA Astrophysics Data System (ADS)

Cole, Michael A.; Powell, David A.; Shadrivov, Ilya V.

2016-10-01

We propose an all dielectric metamaterial that acts as a perfect terahertz absorber without a ground plane. The unit cell consists of a dielectric cylinder embedded in a low index material. In order to achieve near-perfect terahertz absorption (99.5%) we employ impedance matching of the electric and magnetic resonances within the cylinders of the Huygens’ metasurface. The impedance matching is controlled by changing the aspect ratio between the height and diameter of the cylinder. We show that the absorption resonance can be tuned to particular frequencies from 0.3 to 1.9 THz via changing the geometry of the structure while keeping a nearly constant aspect ratio of the cylinders.

15. Measuring THz QCL feedback using an integrated monolithic transceiver.

SciTech Connect

Wanke, Michael Clement

2010-08-01

THz quantum cascade lasers are of interest for use as solid-state local-oscillators in THz heterodyne receiver systems, especially for frequencies exceeding 2 THz and for use with non-cryogenic mixers which require mW power levels. Among other criteria, to be a good local oscillator, the laser must have a narrow linewidth and excellent frequency stability. Recent phase locking measurements of THz QCLs to high harmonics of microwave frequency reference sources as high as 2.7 THz demonstrate that the linewidth and frequency stability of QCLs can be more than adequate. Most reported THz receivers employing QCLs have used discrete source and detector components coupled via mechanically aligned free-space quasioptics. Unfortunately, retroreflections of the laser off of the detecting element can lead to deleterious feedback effects. Using a monolithically integrated transceiver with a Schottky diode monolithically integrated into a THz QCL, we have begun to explore the sensitivity of the laser performance to feedback due to retroreflections of the THz laser radiation. The transceiver allows us to monitor the beat frequency between internal Fabry-Perot modes of the QCL or between a QCL mode and external radiation incident on the transceiver. When some of the power from a free running Fabry-Perot type QCL is retroreflected with quasi-static optics we observe frequency pulling, mode splitting and chaos. Given the lack of calibrated frequency sources with sufficient stability and power to phase lock a QCL above a couple THz, attempts have been made to lock the absolute laser frequency by locking the beat frequency of a multimoded laser. We have phase locked the beat frequency between Fabry-Perot modes to an {approx}13 GHz microwave reference source with a linewidth less than 1 Hz, but did not see any improvment in stability of the absolute frequency of the laser. In this case, when some laser power is retroreflected back into the laser, the absolute frequency can be pulled

16. A BRIGHT IMPULSIVE SOLAR BURST DETECTED AT 30 THz

SciTech Connect

Kaufmann, P.; Fernandes, L. O. T.; Kudaka, A. S.; De Souza, R. V.; Valio, A.; Raulin, J.-P.; White, S. M.; Freeland, S. L.; Marcon, R.; Aballay, J. L.; Fernandez, G.; Godoy, R.; Marun, A.; Gimenez de Castro, C. G.

2013-05-10

Ground- and space-based observations of solar flares from radio wavelengths to gamma-rays have produced considerable insights but raised several unsolved controversies. The last unexplored wavelength frontier for solar flares is in the range of submillimeter and infrared wavelengths. Here we report the detection of an intense impulsive burst at 30 THz using a new imaging system. The 30 THz emission exhibited remarkable time coincidence with peaks observed at microwave, mm/submm, visible, EUV, and hard X-ray wavelengths. The emission location coincides with a very weak white-light feature, and is consistent with heating below the temperature minimum in the atmosphere. However, there are problems in attributing the heating to accelerated electrons. The peak 30 THz flux is several times larger than the usual microwave peak near 9 GHz, attributed to non-thermal electrons in the corona. The 30 THz emission could be consistent with an optically thick spectrum increasing from low to high frequencies. It might be part of the same spectral component found at sub-THz frequencies whose nature remains mysterious. Further observations at these wavelengths will provide a new window for flare studies.

17. THz near-field imaging of biological tissues employing synchrotronradiation

SciTech Connect

Schade, Ulrich; Holldack, Karsten; Martin, Michael C.; Fried,Daniel

2004-12-23

Terahertz scanning near-field infrared microscopy (SNIM) below 1 THz is demonstrated. The near-field technique benefits from the broadband and highly brilliant coherent synchrotron radiation (CSR) from an electron storage ring and from a detection method based on locking onto the intrinsic time structure of the synchrotron radiation. The scanning microscope utilizes conical wave guides as near-field probes with apertures smaller than the wavelength. Different cone approaches have been investigated to obtain maximum transmittance. Together with a Martin-Puplett spectrometer the set-up enables spectroscopic mapping of the transmittance of samples well below the diffraction limit. Spatial resolution down to about lambda/40 at 2 wavenumbers (0.06 THz) is derived from the transmittance spectra of the near-field probes. The potential of the technique is exemplified by imaging biological samples. Strongly absorbing living leaves have been imaged in transmittance with a spatial resolution of 130 mu-m at about 12 wave numbers (0.36 THz). The THz near-field images reveal distinct structural differences of leaves from different plants investigated. The technique presented also allows spectral imaging of bulky organic tissues. Human teeth samples of various thicknesses have been imaged between 2 and 20 wavenumbers (between 0.06and 0.6 THz). Regions of enamel and dentin within tooth samples are spatially and spectrally resolved, and buried caries lesions are imaged through both the outer enamel and into the underlying dentin.

18. First tests of THz transmission through a Diamond Anvil Cell

SciTech Connect

John Klopf

2011-01-24

The THz source generated by the accelerator driver for the Jefferson Lab Free Electron Laser is unique in the world in its ability to deliver a high average power beam of ultrashort (<500 fs FWHM) broadband THz pulses. The spectrum of this source presents an ideal probe for many low energy phenomena, and the time structure enables measurement of dynamic processes with sub-ps resolution. An outline of the range of potential applications for this THz source as a probe of sub-ps dynamics in materials under extreme conditions will be presented. To demonstrate the capabilities of this source for just such experiments, the first set of tests to characterize the transmission of the THz beam through a diamond anvil cell (DAC) have been performed. These preliminary results will be presented along with a description of the optical design used to deliver the THz beam into and out of the DAC. The current design will be compared with other possible techniques and the plans for the next set of measurements will also be given.

19. Non-destructive sub-THz CW imaging

NASA Astrophysics Data System (ADS)

Karpowicz, Nicholas; Zhong, Hua; Xu, Jingzhou; Lin, Kuang-I.; Hwang, Jenn-Shyong; Zhang, Xi-Cheng

2005-03-01

A simple, compact CW sub-THz imaging system, utilizing a 0.2 and 0.6 THz Gunn diode source is presented. A silicon beam lead diode detector and a Golay cell are used for the detection. Various results are presented, which show that the CW THz imaging modality is suitable for diverse applications, such as non-destructive testing and security. The key components of the system include the Gunn diode assembly, an optical chopper, a polyethylene lens, a detector, a lock-in amplifier, and two translation stages. The beam from the Gunn diode is focused on the sample being imaged by the polyethylene lens, the transmitted or reflected beam is measured by the detector. The energy transmitted through the sample at each point in the plane of the sample is detected. Since the system has relatively few components compared to pulsed THz imaging systems, it is less expensive and easier to design and operate, although it does not provide depth or spectral information about the sample. Since no time-delay scans take place, scanning can be done quickly compared to a time-domain system, limited by the maximum velocity of the translation stages and response of the detectors. It provides information about the macroscopic features of hidden structures within materials that are transparent to sub THz radiation, such as space shuttle insulating foam, articles of clothing, and luggage.

20. THz Pulse Detection by Multilayered GeTe/Sb2Te3.

PubMed

Makino, Kotaro; Kuromiya, Shota; Takano, Keisuke; Kato, Kosaku; Nakajima, Makoto; Saito, Yuta; Tominaga, Junji; Iida, Hitoshi; Kinoshita, Moto; Nakano, Takashi

2016-11-30

We proposed and demonstrated terahertz (THz) pulse detection by means of multilayered GeTe/Sb2Te3 phase-change memory materials that are also known as a multilayer topological insulator-normal insulator (MTN) system. THz time-domain spectroscopy measurement was performed for MTN films with different multilayer repetitions as well as a conventional as-grown Ge-Te-Sb (GST) alloy film. It was found that MTNs absorb THz waves and that the absorption coefficient depends on the number of layers, while the as-grown GST alloy film was almost transparent for THz waves. Simple MTN-based THz detection devices were fabricated, and the THz-induced change in the current signal was measured when a DC bias voltage was applied between the electrodes. We confirmed that irradiation of THz pulse causes a decrease in the resistance of the MTNs. This result indicates that our devices are capable of THz detection.

1. Self-organization approach for THz polaritonic metamaterials

SciTech Connect

Reyes-Coronado, A.; Acosta, M.F.; Merino, R.I.; Orera,, V.M.; Kenanakis, G.; Katsarakis, n.; Kafesaki, M.; Mavidis, Ch.; Garcia de Abajo, J.; Economou, E.N.; Soukoulis, Costas M.

2012-06-15

In this paper we discuss the fabrication and the electromagnetic (EM) characterization of anisotropic eutectic metamaterials, consisting of cylindrical polaritonic LiF rods embedded in either KCl or NaCl polaritonic host. The fabrication was performed using the eutectics directional solidification self-organization approach. For the EM characterization the specular reflectance at far infrared, between 3 THz and 11 THz, was measured and also calculated by numerically solving Maxwell equations, obtaining good agreement between experimental and calculated spectra. Applying an effective medium approach to describe the response of our samples, we predicted a range of frequencies in which most of our systems behave as homogeneous anisotropic media with a hyperbolic dispersion relation, opening thus possibilities for using them in negative refractive index and imaging applications at THz range.

2. THz-wave parametric source and its imaging applications

NASA Astrophysics Data System (ADS)

Kawase, Kodo

2004-08-01

Widely tunable coherent terahertz (THz) wave generation has been demonstrated based on the parametric oscillation using MgO doped LiNbO3 crystal pumped by a Q-switched Nd:YAG laser. This method exhibits multiple advantages like wide tunability, coherency and compactness of its system. We have developed a novel basic technology for terahertz (THz) imaging, which allows detection and identification of chemicals by introducing the component spatial pattern analysis. The spatial distributions of the chemicals were obtained from terahertz multispectral transillumination images, using absorption spectra previously measured with a widely tunable THz-wave parametric oscillator. Further we have applied this technique to the detection and identification of illicit drugs concealed in envelopes. The samples we used were methamphetamine and MDMA, two of the most widely consumed illegal drugs in Japan, and aspirin as a reference.

3. Cooling of radiative quantum dot excitons by THz-radiation

NASA Astrophysics Data System (ADS)

Boxberg, Fredrik; Tulkki, Jukka; Yusa, Go; Sakaki, Hiroyuki

2007-04-01

Yusa et al. reported an anomalous cooling of radiative quantum dot (QD) excitons by THz-radiation in [Proc. 24th ICPS, 1083 (1998)] We have analyzed this experiment using continuum elasticity, multi-band kṡp and spin-resolved Monte-Carlo methods. We show that the unexpected discovery is related to hole relaxation via piezo-electric potential minima, induced in the QD sample by InP stressor islands. The THz-radiation gives rise to a drift of dark excitons from the piezo-electric minima to radiative states in the deformation potential minimum. This increases the QD ground state luminescence at the expense of the luminescence from higher QD states. We reproduce also the delayed flash of QD ground state luminescences when a THz-radiation pulse hits the sample even ˜ 1 s after switching off the carrier generation.

4. 2.7 THz Balanced Waveguide HEB Mixer

NASA Astrophysics Data System (ADS)

Boussaha, Faouzi; Kawamura, Jonathan; Stern, Jeffery; Jung-Kubiak, Cecile

2014-09-01

We report on the development of a waveguide-based balanced superconducting mixer for operation near 2.7 THz. The mixer employs a pair of NbN hot-electron bolometers defined on 6 μm-thick silicon substrate that follows a 90° hybrid coupler. To produce the critical structures of the coupler and waveguide embedding circuit, we have utilized silicon micromachining techniques based on deep reactive ion etching. Operating near 4.2 K bath temperature, we have measured a minimum uncorrected DSB receiver noise temperature of less than 2000 K using Callen-Welton formula and local oscillator sideband noise rejection better than 13 3 dB at 2.74 THz. The concept is suitable for building arrays, readily scalable for higher frequencies up 5 THz, and could accommodate other mixer technologies, such as room-temperature Schottky diode mixers.

5. Filling the THz Gap - High Power Sources and Applications

SciTech Connect

Gwyn Williams

2006-02-01

Electromagnetic waves centered at a frequency of 1 THz lie between photonics on the one hand and electronics on the other, and are very hard to generate and detect. However, since the THz part of the spectrum is energetically equivalent to many important physical, chemical and biological processes including superconducting gaps and protein dynamical processes, it is of great interest to facilitate experimental research in this region. This has stimulated major steps in the past decade for filling this gap in the usable spectrum. In this review paper we describe the evolution of a new generation of sources that boost the average power available in the THz region by more than a million-fold, making this region routinely accessible for the first time. This is achieved using two enhancement factors, namely relativistic electrons and super-radiance. We will also point to the scientific potential for discovery that is now enabled in this region.

6. Geometrical Aberration Suppression for Large Aperture Sub-THz Lenses

NASA Astrophysics Data System (ADS)

Rachon, M.; Liebert, K.; Siemion, A.; Bomba, J.; Sobczyk, A.; Knap, W.; Coquillat, D.; Suszek, J.; Sypek, M.

2017-03-01

Advanced THz setups require high performance optical elements with large numerical apertures and small focal lengths. This is due to the high absorption of humid air and relatively low efficiency of commercially available detectors. Here, we propose a new type of double-sided sub-THz diffractive optical element with suppressed geometrical aberration for narrowband applications (0.3 THz). One side of the element is designed as thin structure in non-paraxial approach which is the exact method, but only for ideally flat elements. The second side will compensate phase distribution differences between ideal thin structure and real volume one. The computer-aided optimization algorithm is performed to design an additional phase distribution of correcting layer assuming volume designing of the first side of the element. The experimental evaluation of the proposed diffractive component created by 3D printing technique shows almost two times larger performance in comparison with uncorrected basic diffractive lens.

7. Geometrical Aberration Suppression for Large Aperture Sub-THz Lenses

NASA Astrophysics Data System (ADS)

Rachon, M.; Liebert, K.; Siemion, A.; Bomba, J.; Sobczyk, A.; Knap, W.; Coquillat, D.; Suszek, J.; Sypek, M.

2016-11-01

Advanced THz setups require high performance optical elements with large numerical apertures and small focal lengths. This is due to the high absorption of humid air and relatively low efficiency of commercially available detectors. Here, we propose a new type of double-sided sub-THz diffractive optical element with suppressed geometrical aberration for narrowband applications (0.3 THz). One side of the element is designed as thin structure in non-paraxial approach which is the exact method, but only for ideally flat elements. The second side will compensate phase distribution differences between ideal thin structure and real volume one. The computer-aided optimization algorithm is performed to design an additional phase distribution of correcting layer assuming volume designing of the first side of the element. The experimental evaluation of the proposed diffractive component created by 3D printing technique shows almost two times larger performance in comparison with uncorrected basic diffractive lens.

8. Radiative Characteristics of On-Chip Terahertz (THz) Structures

SciTech Connect

Hussein, Yasser A.; Spencer, James E.; /SLAC

2005-06-07

Previously, we explored possibilities for producing narrow-band THz radiation using either free or bound electrons (solid state) in micro-undulatory configurations [1] because integrated circuit technology appeared well matched to this region extending from about 300 GHz to 30 THz. This range [2]-[3] has largely been neglected until recently because it runs from the limit of WR-3 waveguide around 300 GHz up to CO{sub 2} lasers where the laser regime becomes dominant. There are mainly two approaches for generating THz radiation, i.e. through free or bound electron (BE) implementations. In this paper, emphasis is on producing this radiation using bound electrons via IC technology but in close analogy to free electron lasers (FELs) that are comparatively immense, expensive, need high power and have low efficiencies [4].

9. Active tunable plasmonically induced polarization conversion in the THz regime

NASA Astrophysics Data System (ADS)

Ling, Furi; Yao, Gang; Yao, Jianquan

2016-10-01

A plasmon-induced polarization conversion (PIPC) structure based on periodically patterned graphene was demonstrated in the THz regime. By varying the Fermi level of two connected T-shape graphene strips through the electrostatic gating, the peak frequency and the group index in the transparency window can be tuned, which is good agreement with the coupled Lorentz oscillator model. Due to interference between two polarization selective graphene plasmonic resonances coexisting in the planar metamaterial, polarization conversion can be achieved. The linearly polarized THz wave can be converted to elliptically and right circularly polarized THz wave through varying the relaxation time of electrons in graphene. This novel chip-scale active terahertz device promises essential application opportunities in terahertz sensing and terahertz communications.

10. Relative Infrared (IR) and Terahertz (THz) Signatures of Common Explosives

SciTech Connect

Sharpe, Steven W.; Johnson, Timothy J.; Sheen, David M.; Atkinson, David A.

2006-11-13

Pacific Northwest National Laboratory (PNNL) has recently recorded the infrared (IR) and far-infrared (sometimes called the terahertz, THz) spectral signatures of four common explosives, in the condensed phase. The signatures of RDX, PETN, TNT and Tetryl were recorded both in the infrared and the THz domains, using Fourier transform infrared (FTIR) spectroscopy. Samples consisted of thin films and were made by depositing and subsequent evaporation of an acetone-explosive mixture. The complete spectrum spanned the range from 4,000 to 8 cm-1 at 2.0 cm-1 spectral resolution. Preliminary results in the infrared agree with those of previous workers, while the THz signatures are one order of magnitude weaker than the strongest IR bands.

11. Optimization of THz Radiation Generation from a Laser Wakefield Accelerator

SciTech Connect

Plateau, G. R.; Matlis, N. H.; Toth, C.; Geddes, C. G. R.; Schroeder, C. B.; Tilborg, J. van; Albert, O.; Esarey, E.; Leemans, W. P.

2009-01-22

Ultrashort terahertz pulses with energies in the {mu}J range can be generated with laser wakefield accelerators (LWFA), which are novel, compact accelerators that produce ultrashort electron bunches with energies up to 1 GeV and energy spreads of a few-percent. Laser pulses interacting with a plasma create accelerated electrons which upon exiting the plasma emit terahertz pulses via transition radiation. Because these electron bunches are ultrashort (<50 fs), they can radiate coherently (coherent transition radiation--CTR) in a wide bandwidth ({approx}1-10 THz) yielding high intensity terahertz pulses. In addition to providing a non-invasive bunch-length diagnostic and thus feedback for the LWFA, these high peak power THz pulses are suitable for high field (MV/cm) pump-probe experiments. Here we present energy-based measurements using a Golay cell and an electro-optic technique which were used to characterize these THz pulses.

12. New developments in THz quartz enhanced photoacoustic spectroscopy

NASA Astrophysics Data System (ADS)

Spagnolo, Vincenzo; Patimisco, Pietro; Sampaolo, Angelo; Giglio, Marilena; Vitiello, Miriam S.; Scamarcio, Gaetano; Tittel, Frank K.

2016-09-01

We will report on new developments of quartz-enhanced photo-acoustic (QEPAS) sensor employing THz quantum cascade laser (QCLs). The extension of the QEPAS technique in the THz range was made possible by the realization of custom made QTFs. With the aim to improve the QTF acousto-electric transduction efficiency, we designed and realized new QTF designs. A detailed analysis of the quality factor, the resonance frequency and the electrical resistance of custom quartz tuning forks (QTFs) with different geometrical parameters is reported. The custom QTFs were employed in QEPAS sensors using THz QCLs as the laser excitation sources and targeting CH3OH and H2S. Minimum detection limits of a few tens of ppb and normalized noise equivalent absorption factors down to 3.75×10-11 cm-1W/Hz½ were achieved.

13. Active tunable plasmonically induced polarization conversion in the THz regime

PubMed Central

Ling, Furi; Yao, Gang; Yao, Jianquan

2016-01-01

A plasmon-induced polarization conversion (PIPC) structure based on periodically patterned graphene was demonstrated in the THz regime. By varying the Fermi level of two connected T-shape graphene strips through the electrostatic gating, the peak frequency and the group index in the transparency window can be tuned, which is good agreement with the coupled Lorentz oscillator model. Due to interference between two polarization selective graphene plasmonic resonances coexisting in the planar metamaterial, polarization conversion can be achieved. The linearly polarized THz wave can be converted to elliptically and right circularly polarized THz wave through varying the relaxation time of electrons in graphene. This novel chip-scale active terahertz device promises essential application opportunities in terahertz sensing and terahertz communications. PMID:27734912

14. Method for the production of wideband THz radiation

DOEpatents

Krafft, Geoffrey A.

2008-01-01

A method for the production of extremely wide bandwidth THz radiation comprising: delivering an electron beam from a source to an undulator that does not deflect the angle or transversely move the electron beam; and optimizing the undulator to yield peak emission in the middle of the THz band (1 THz). These objectives are accomplished by magnetically bending the orbit of the incoming electron beam in the undulator according to the function x(z)=x.sub.o exp(-z.sup.2/2.sigma..sup.2) and controlling the transverse magnetic field to be B(z)=B.sub.0(1-z.sup.2/.sigma..sup.2)exp(-z.sup.2/2.sigma..sup.2).

15. Preliminary results of non-contact THz imaging of cornea

NASA Astrophysics Data System (ADS)

Sung, Shijun; Garritano, James; Bajwa, Neha; Deng, Sophie; Hubschman, Jean-Pierre; Grundfest, Warren S.; Taylor, Zachary D.

2015-03-01

This paper presents a novel THz optical design that allows the acquisition of THz reflectivity maps of in vivo cornea without the need for a field flattening window and preliminary imaging results of in vivo rabbit cornea. The system's intended use is to sense small changes in corneal tissue water content (CTWC) that can be precursors for a host of diseases and pathologies. Unique beam optics allows the scanning of a curved surface at normal incidence while keeping the source detector and target stationary. Basic system design principles are discussed and image sets of spherical calibration targets and corneal phantom models are presented. The presented design will enable, for the first time, non-contact THz imaging of animal and human cornea.

16. Characteristics of THz carrier dynamics in GaN thin film and ZnO nanowires by temperature dependent terahertz time domain spectroscopy measurement

NASA Astrophysics Data System (ADS)

Balci, Soner; Baughman, William; Wilbert, David S.; Shen, Gang; Kung, Patrick; Kim, Seongsin Margaret

2012-12-01

We present a comprehensive study of the characteristics of carrier dynamics using temperature dependent terahertz time domain spectroscopy. By utilizing this technique in combination with numerical calculations, the complex refractive index, dielectric function, and conductivity of n-GaN, undoped ZnO NWs, and Al-doped ZnO NWs were obtained. The unique temperature dependent behaviors of major material parameters were studied at THz frequencies, including plasma frequency, relaxation time, carrier concentration and mobility. Frequency and temperature dependent carrier dynamics were subsequently analyzed in these materials through the use of the Drude and the Drude-Smith models.

17. Structure and performance of dielectric films based on self-assembled nanocrystals with a high dielectric constant

SciTech Connect

Huang, LM; Liu, SY; Van Tassell, BJ; Liu, XH; Byro, A; Zhang, HN; Leland, ES; Akins, DL; Steingart, DA; Li, J; O'Brien, S

2013-09-24

Self-assembled films built from nanoparticles with a high dielectric constant are attractive as a foundation for new dielectric media with increased efficiency and range of operation, due to the ability to exploit nanofabrication techniques and emergent electrical properties originating from the nanoscale. However, because the building block is a discrete one-dimensional unit, it becomes a challenge to capture potential enhancements in dielectric performance in two or three dimensions, frequently due to surface effects or the presence of discontinuities. This is a recurring theme in nanoparticle film technology when applied to the realm of thin film semiconductor and device electronics. We present the use of chemically synthesized. (Ba; Sr)TiO3 nanocrystals, and a novel deposition-polymerization technique, as a means to fabricate the dielectric layer. The effective dielectric constant of the film is tunable according to nanoparticle size, and effective film dielectric constants of up to 34 are enabled. Wide area and multilayer dielectrics of up to 8 cm(2) and 190 nF are reported, for which the building block is an 8 nm nanocrystal. We describe models for assessing dielectric performance, and distinct methods for improving the dielectric constant of a nanocrystal thin film. The approach relies on evaporatively driven assembly of perovskite nanocrystals with uniform size distributions in a tunable 7-30 nm size range, coupled with the use of low molecular weight monomer/polymer precursor chemistry that can infiltrate the porous nanocrystal thin film network post assembly. The intercrystal void space (low k dielectric volume fraction) is minimized, while simultaneously promoting intercrystal connectivity and maximizing volume fraction of the high k dielectric component. Furfuryl alcohol, which has good affinity to the surface of. (Ba; Sr ) TiO3 nanocrystals and miscibility with a range of solvents, is demonstrated

18. Dielectric behaviors of typical benzene monosubstitutes, bromobenzene and benzonitrile.

PubMed

Shikata, Toshiyuki; Sugimoto, Natsuki; Sakai, Yuji; Watanabe, Junji

2012-10-18

The dielectric behaviors of typical benzene monosubstitutes, bromobenzene (Br-Bz) and benzonitrile (NC-Bz), were investigated up to 3 THz in the pure liquid state over a temperature range from 10 to 60 °C to understand differences in molecular motions of these simple, planar molecules bearing rather different electric dipole moments: 1.72 and 4.48 D for Br-Bz and NC-Bz in gaseous state, respectively. Temperature dependence of spin-lattice relaxation time (T(1)) for (13)C NMR and viscosities for these liquids were also determined to obtain information for molecular motions. Moreover, depolarized Rayleigh scattering (DRS) experiments were carried out for both liquids at 20 °C to determine frequency dependencies of optical susceptibilities up to 8 THz directly relating to rotational motions of their molecular planes. Most Br-Bz molecules rotate freely over a temperature range examined, showing a Kirkwood correlation factor close to g(K) ∼ 1.0 at dielectric Debye-type relaxation times (ca. 18 ps at 20 °C) essentially identical to microscopic (dielectric) relaxation times evaluated from T(1)(13)C NMR data. A small amount of Br-Bz molecules forms dimeric intermolecular associations in an antiparallel configuration of dipole moments. On the other hand, NC-Bz molecules form stable dimers in the antiparallel dipole configuration at a population much higher than that of Br-Bz because of a markedly greater dipole moment than that of Br-Bz. A major dielectric relaxation mechanism for NC-Bz found at ca. 70 ps at 20 °C results from the dissociation process of dimers with a lifetime longer than a rotational relaxation time, observable as a minor dielectric relaxation mechanism at ca. 12 ps at 20 °C, of individual monomeric NC-Bz molecules without the formation of dimers. The formation of stable dimers in an antiparallel configuration is responsible for the observed small g(K) values, ca. 0.5, and disagreement between major (or minor) dielectric relaxation times and

19. THz Communications using Photonics and Electronic Devices: the Race to Data-Rate

NASA Astrophysics Data System (ADS)

Ducournau, Guillaume; Szriftgiser, Pascal; Pavanello, Fabio; Peytavit, Emilien; Zaknoune, Mohammed; Bacquet, Denis; Beck, Alexandre; Akalin, Tahsin; Lampin, Jean-François; Lampin, Jean-François

2015-02-01

With the mass development of mobile data transfers, wireless communications have recently entered a new area: the carrier frequency is now entering the THz region. After a brief overview of context and key features of THz communication, focus is given on photonic-based THz emitters based on quasi-optic UTC-PDs. A special design of wideband photomixer is presented and its applications for narrow bandwidth THz generation. Using this photomixer, communication links at 200, 400 and 600 GHz are presented.

20. Identifying the distinct phases of THz waves from K-valley electrons in graphite

SciTech Connect

Irfan, Muhammad; Yim, Jong-Hyuk Jho, Young-Dahl; Kim, Changyoung

2013-12-04

The polarity change of THz electromagnetic waves radiated from single-crystalline graphite and polycrystalline graphite films has been studied to identify the main generation mechanism in conventional reflective THz time-domain spectroscopy scheme. The excitation wavelength variation around the K-valley produces no significant changes in THz field strength. We further found that THz waves become fully dispersed without polarity change in lateral detection geometry.

1. Component pattern analysis of chemicals using multispectral THz imaging system

NASA Astrophysics Data System (ADS)

Kawase, Kodo; Ogawa, Yuichi; Watanabe, Yuki

2004-04-01

We have developed a novel basic technology for terahertz (THz) imaging, which allows detection and identification of chemicals by introducing the component spatial pattern analysis. The spatial distributions of the chemicals were obtained from terahertz multispectral transillumination images, using absorption spectra previously measured with a widely tunable THz-wave parametric oscillator. Further we have applied this technique to the detection and identification of illicit drugs concealed in envelopes. The samples we used were methamphetamine and MDMA, two of the most widely consumed illegal drugs in Japan, and aspirin as a reference.

2. Functional multi-band THz meta-foils

PubMed Central

Wu, Jianfeng; Moser, Herbert O.; Xu, Su; Jian, Linke; Banas, Agnieszka; Banas, Krzysztof; Chen, Hongsheng; Bettiol, Andrew A.; Breese, Mark B. H.

2013-01-01

In this paper, we present the first experimental demonstration of double- and triple-band negative refraction index meta-foils in the terahertz (THz) region. Multi-band meta-foils constructed by multi-cell S-string resonators in a single structure exhibit simultaneously negative permittivity and negative permeability responses at multiple frequencies. The phenomena are confirmed by numerical simulations and Fourier transform infrared spectroscopy measurements. The flexible, freestanding multi-band meta-foils provide a promising candidate for the development of multi-frequency THz materials and devices. PMID:24346309

3. Very high power THz radiation at Jefferson Lab

SciTech Connect

Carr, G.L.; Martin, Michael C.; McKinney, Wayne R.; Jordan, K.; Neil, George R.; Williams, G.P.

2002-03-31

We report the production of high power (20 watts average, {approx};1 Megawatt peak) broadband THz light based on coherent emission from relativistic electrons. We describe the source, presenting theoretical calculations and their experimental verification. For clarity we compare this source with one based on ultrafast laser techniques, and in fact the radiation has qualities closely analogous to that produced by such sources, namely that it is spatially coherent, and comprises short duration pulses with transform-limited spectral content. In contrast to conventional THz radiation, however, the intensity is many orders of magnitude greater due to the relativistic enhancement.

4. Very high Power THz radiation at Jefferson Lab

SciTech Connect

G.L. Carr; Michael C. Martin; Wayne R. McKinney; Kevin Jordan; George R. Neil; Gwyn P. Williams

2002-03-01

We report the production of high power (20 watts average, {approx}1 Megawatt peak) broadband THz light based on coherent emission from relativistic electrons. We describe the source, presenting theoretical calculations and their experimental verification. For clarity we compare this source with one based on ultrafast laser techniques, and in fact the radiation has qualities closely analogous to that produced by such sources, namely that it is spatially coherent, and comprises short duration pulses with transform-limited spectral content. In contrast to conventional THz radiation, however, the intensity is many orders of magnitude greater due to the relativistic enhancement.

5. Very high power THz radiation at Jefferson Lab.

PubMed

Carr, G L; Martin, Michael C; McKinney, Wayne R; Jordan, K; Neil, George R; Williams, G P

2002-11-07

We report the production of high power (20 W average, approximately 1 MW peak) broadband THz light based on coherent emission from relativistic electrons. We describe the source, presenting theoretical calculations and their experimental verification. For clarity we compare this source with that based on ultrafast laser techniques, and in fact the radiation has qualities closely analogous to those produced by such sources, namely that it is spatially coherent, and comprises short duration pulses with transform-limited spectral content. In contrast to conventional THz radiation, however, the intensity is many orders of magnitude greater due to the relativistic enhancement.

6. Optical and THz reflectance investigations of organic solar cells

NASA Astrophysics Data System (ADS)

Sporea, Dan; Mihai, Laura; Sporea, Adelina; Galagan, Yulia

2016-04-01

Two Organic Photovoltaic devices having a photoactive layer containing Poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5- (4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM, 99%), and the layer sequences - glass/ITO/ZnO/PAL/PEDOT:PSS/Ag/encapsulation were non-destructively investigated by diffuse optical spectral reflectance, THz spectroscopy and THz imaging. The proposed methods proved to be powerful tools to support quality assurance in organic solar cells development, facilitating both the localization of manufacturing defects and the device degradation, as they are combined with "classical" evaluation means.

7. Resonant metamaterial detectors based on THz quantum-cascade structures

PubMed Central

Benz, A.; Krall, M.; Schwarz, S.; Dietze, D.; Detz, H.; Andrews, A. M.; Schrenk, W.; Strasser, G.; Unterrainer, K.

2014-01-01

We present the design, fabrication and characterisation of an intersubband detector employing a resonant metamaterial coupling structure. The semiconductor heterostructure relies on a conventional THz quantum-cascade laser design and is operated at zero bias for the detector operation. The same active region can be used to generate or detect light depending on the bias conditions and the vertical confinement. The metamaterial is processed directly into the top metal contact and is used to couple normal incidence radiation resonantly to the intersubband transitions. The device is capable of detecting light below and above the reststrahlenband of gallium-arsenide corresponding to the mid-infrared and THz spectral region. PMID:24608677

8. Free-Space Imaging Technology For THz Beams

DTIC Science & Technology

2006-05-31

1513, 2001. • B. Ferguson , S. Wang, D. Gray, D. Abbott, and X.-C. Zhang, “THz wave computed tomography,” Optics Letters, 27, 1312, 2002. • THz...measurement of time-domain with phase and timing data provides tomographic imaging with spectroscopic information. REFERENCES [1] B. Ferguson and X.-C. Zhang...spatiotemporal terahertz field imaging,” Optics Letters 23(14), pp. 1114–1116, 1998. [11] D. D. Arnone, C. M. Ciesla, A. Corchia, S. Egusa, M. Pepper

9. Independent component analysis applications on THz sensing and imaging

NASA Astrophysics Data System (ADS)

Balci, Soner; Maleski, Alexander; Nascimento, Matheus Mello; Philip, Elizabath; Kim, Ju-Hyung; Kung, Patrick; Kim, Seongsin M.

2016-05-01

We report Independent Component Analysis (ICA) technique applied to THz spectroscopy and imaging to achieve a blind source separation. A reference water vapor absorption spectrum was extracted via ICA, then ICA was utilized on a THz spectroscopic image in order to clean the absorption of water molecules from each pixel. For this purpose, silica gel was chosen as the material of interest for its strong water absorption. The resulting image clearly showed that ICA effectively removed the water content in the detected signal allowing us to image the silica gel beads distinctively even though it was totally embedded in water before ICA was applied.

10. Novel Materials with Effective Super Dielectric Constants for Energy Storage

NASA Astrophysics Data System (ADS)

Cortes, Francisco Javier Quintero; Phillips, Jonathan

2015-05-01

To test a theory of the recently discovered phenomenon of super dielectric behavior at very low frequency, the dielectric constants of several pastes', composed of porous alumina powders filled to the point of incipient wetness with water containing dissolved sodium chloride, were measured. The effective dielectric low frequency constants of some of the pastes were greater than 1010, dramatically higher than that of any material ever reported. Moreover, the total energy density reported for one capacitor generated with NaCl-based super dielectric material is marginally higher than found in any prior report. These results are consistent with this recently postulated model of low frequency super dielectric behavior in porous, non-conductive materials saturated with ion-containing liquids: upon the application of an electric field, ions dissolved in the saturating liquid contained in the pores will travel to the ends of pore-filling liquid droplets creating giant dipoles. The fields of these giant dipoles oppose the applied field, reducing the net field created per unit of charge on the capacitor plates, effectively increasing charge/voltage ratio, hence capacitance. This is simply a version of the theory of polarizable media' found in most classic texts on electromagnetism. Other observations reported here include (1) the impact of ion concentration on dielectric values, (2) a maximum voltage similar to that associated with the electrical breakdown of water, (3) the loss of capacitance upon drying, (4) the recovery of capacitance upon the addition of water to a dry super dielectric material, and (5) the linear relationship between capacitance and inverse thickness. All observations are consistent with the earlier proposed model of the super dielectric phenomenon. An extrapolation of results suggests this technology can lead to energy density greater than the best lithium-ion battery.

11. Measuring the dielectric properties of soil-organic mixtures using coaxial impedance dielectric reflectometry

NASA Astrophysics Data System (ADS)

Francisca, Franco M.; Montoro, Marcos A.

2012-05-01

Contamination of soils with non-aqueous phase liquids (NAPLs) is frequently produced by accidental spills and storage tanks or pipes leakage. The main goals dealing with soil and groundwater contamination include determining the extension of the affected zone, monitoring the contaminant plume and quantifying the pollution degree. The objective of this work is to evaluate the potential of dielectric permittivity measurements to detect the presence of NAPLs in sands. Tested samples were fine, medium, coarse and silty sand with different volumetric contents of water and paraffin oil. The dielectric permittivity was measured by means of a Coaxial Impedance Dielectric Reflectometry method in specimens with either known fluid content or at different stages during immiscible displacement tests. A simplified method was developed to quantify the amount of oil from dielectric permittivity measurements and effective mixture media models. Obtained results showed that groundwater contamination with NAPL and the monitoring of immiscible fluid displacement in saturated porous media can be clearly identified from dielectric measurements. Finally, very accurate results can be obtained when computing the contamination degree with the proposed method in comparison with the real volumetric content of NAPL (r2 > 90%).

12. Resonant dielectric metamaterials

DOEpatents

Loui, Hung; Carroll, James; Clem, Paul G; Sinclair, Michael B

2014-12-02

A resonant dielectric metamaterial comprises a first and a second set of dielectric scattering particles (e.g., spheres) having different permittivities arranged in a cubic array. The array can be an ordered or randomized array of particles. The resonant dielectric metamaterials are low-loss 3D isotropic materials with negative permittivity and permeability. Such isotropic double negative materials offer polarization and direction independent electromagnetic wave propagation.

13. Thin InSb layers with metallic gratings: a novel platform for spectrally-selective THz plasmonic sensing.

PubMed

Lin, Shuai; Bhattarai, Khagendra; Zhou, Jiangfeng; Talbayev, Diyar

2016-08-22

We present a computational study of terahertz optical properties of a grating-coupled plasmonic structure based on micrometer-thin InSb layers. We find two strong absorption resonances that we interpret as standing surface plasmon modes and investigate their dispersion relations, dependence on InSb thickness, and the spatial distribution of the electric field. The observed surface plasmon modes are well described by a simple theory of the air/InSb/air tri-layer. The plasmonic response of the grating/InSb structure is highly sensitive to the dielectric environment and the presence of an analyte (e.g., lactose) at the InSb interface, which is promising for terahertz plasmonic sensor applications. We determine the sensor sensitivity to be 7200 nm per refractive index unit (or 0.06 THz per refractive index unit). The lower surface plasmon mode also exhibits a splitting when tuned in resonance with the vibrational mode of lactose at 1.37 THz. We propose that such interaction between surface plasmon and vibrational modes can be used as the basis for a new sensing modality that allows the detection of terahertz vibrational fingerprints of an analyte.

14. Inductive dielectric analyzer

NASA Astrophysics Data System (ADS)

Agranovich, Daniel; Polygalov, Eugene; Popov, Ivan; Ben Ishai, Paul; Feldman, Yuri

2017-03-01

One of the approaches to bypass the problem of electrode polarization in dielectric measurements is the free electrode method. The advantage of this technique is that, the probing electric field in the material is not supplied by contact electrodes, but rather by electromagnetic induction. We have designed an inductive dielectric analyzer based on a sensor comprising two concentric toroidal coils. In this work, we present an analytic derivation of the relationship between the impedance measured by the sensor and the complex dielectric permittivity of the sample. The obtained relationship was successfully employed to measure the dielectric permittivity and conductivity of various alcohols and aqueous salt solutions.

15. Very high Power THz radiation from Relativistic Electrons

SciTech Connect

G.L. Carr; Michael C. Martin; Wayne R. McKinney; Kevin Jordan; George R. Neil; Gwyn P. Williams

2002-08-01

We report the production of high power (20 watts average, {approx}1 Megawatt peak) broadband THz light based on coherent emission from relativistic electrons. We describe the source, presenting theoretical calculations and their experimental verification. For clarity we compare this source with one based on ultrafast laser techniques.

16. New algorithm for the passive THz image quality enhancement

NASA Astrophysics Data System (ADS)

Trofimov, Vyacheslav A.; Trofimov, Vladislav V.

2016-04-01

We propose a new approach for THz image quality enhancing using correlation function between the image under consideration and a standard image. The standard image moves in two directions along a image under analysis. As a result, 2 D correlation function is obtained. Multiplying this function by color number belonging to a grey scale, we restore the image under the analysis. This allows to suppress a noise on a new image. This method allows to see the person clothes details that it means multi-times increasing of the passive THz camera temperature resolution. We discuss a choice of standard image characteristics for an achievement of correlation function for high contrast. Other feature of our approach arises from a possibility of a person image coming to the THz camera by using a computer processing of the image only. It means that we can "decrease" a distance between a person and the passive THz camera. This algorithm is very convenient for using and has a high performance.

17. New THz sources for bio-medical imaging

NASA Astrophysics Data System (ADS)

Harris, James S., Jr.; Gu, Anjia; Kim, Seongsin M.

2007-02-01

We present an evaluation of new terahertz sources for biomedical imaging based upon quantum cascade lasers (QCL) and orientation patterned gallium arsenide (OP-GaAs) optical parametric oscillator (OPO). The recently developed terahertz quantum cascade laser emits a peak output power of up to 40mW at 3.7 THz (λ=81μm). Utilizing coherent terahertz radiation greatly improves the signal to noise ratio of the detection, where it provides a relatively large dynamic range and high spatial resolution. We demonstrated biomedical imaging of malignant tissue contrast in an image of a mouse liver with developed tumors with a THz imaging system based on a QCL. In addition, images of various tissues, such as lung, liver, and brain sections from the laboratory mouse were also obtained. We also explored distinct images from fat, muscle and tendon and measured the absorption coefficient and compared this with FTIR measurements. Another recent technological advance in THz source is based on cascaded optical down-conversion in an OP-GaAs OPO, which provides a tunable THz source over a broad wavelength range with an average power of 1mW at room temperature (RT). The tunability of the OPO source provides additional imaging modes through the ability to excite molecular vibrations and obtain biochemical and structural information in addition to normal absorption or reflectivity contrast.

18. High-resolution waveguide THz spectroscopy of biological molecules.

PubMed

Laman, N; Harsha, S Sree; Grischkowsky, D; Melinger, Joseph S

2008-02-01

Low-frequency vibrational modes of biological molecules consist of intramolecular modes, which are dependent on the molecule as a whole, as well as intermolecular modes, which arise from hydrogen-bonding interactions and van der Waals forces. Vibrational modes thus contain important information about conformation dynamics of biological molecules, and can also be used for identification purposes. However, conventional Fourier transform infrared spectroscopy and terahertz time-domain spectroscopy (THz-TDS) often result in broad, overlapping features that are difficult to distinguish. The technique of waveguide THz-TDS has been recently developed, resulting in sharper features. For this technique, an ordered polycrystalline film of the molecule is formed on a metal sample plate. This plate is incorporated into a metal parallel-plate waveguide and probed via waveguide THz-TDS. The planar order of the film reduces the inhomogeneous broadening, and cooling of the samples to 77K reduces the homogenous broadening. This combination results in the line-narrowing of THz vibrational modes, in some cases to an unprecedented degree. Here, this technique has been demonstrated with seven small biological molecules, thymine, deoxycytidine, adenosine, D-glucose, tryptophan, glycine, and L-alanine. The successful demonstration of this technique shows the possibilities and promise for future studies of internal vibrational modes of large biological molecules.

19. Broadband THz Spectroscopy of 2D Nanoscale Materials

NASA Astrophysics Data System (ADS)

Chen, Lu; Tripathi, Shivendra; Huang, Mengchen; Hsu, Jen-Feng; D'Urso, Brian; Lee, Hyungwoo; Eom, Chang-Beom; Irvin, Patrick; Levy, Jeremy

Two-dimensional (2D) materials such as graphene and transition-metal dichalcogenides (TMDC) have attracted intense research interest in the past decade. Their unique electronic and optical properties offer the promise of novel optoelectronic applications in the terahertz regime. Recently, generation and detection of broadband terahertz (10 THz bandwidth) emission from 10-nm-scale LaAlO3/SrTiO3 nanostructures created by conductive atomic force microscope (c-AFM) lithography has been demonstrated . This unprecedented control of THz emission at 10 nm length scales creates a pathway toward hybrid THz functionality in 2D-material/LaAlO3/SrTiO3 heterostructures. Here we report initial efforts in THz spectroscopy of 2D nanoscale materials with resolution comparable to the dimensions of the nanowire (10 nm). Systems under investigation include graphene, single-layer molybdenum disulfide (MoS2), and tungsten diselenide (WSe2) nanoflakes. 1. Y. Ma, et al., Nano Lett. 13, 2884 (2013). We gratefully acknowledge financial support from the following agencies and grants: AFOSR (FA9550-12-1-0268 (JL, PRI), FA9550-12-1-0342 (CBE)), ONR (N00014-13-1-0806 (JL, CBE), N00014-15-1-2847 (JL)), NSF DMR-1124131 (JL, CBE) and DMR-1234096 (CBE).

20. THz optical design considerations and optimization for medical imaging applications

NASA Astrophysics Data System (ADS)

Sung, Shijun; Garritano, James; Bajwa, Neha; Nowroozi, Bryan; Llombart, Nuria; Grundfest, Warren; Taylor, Zachary D.

2014-09-01

THz imaging system design will play an important role making possible imaging of targets with arbitrary properties and geometries. This study discusses design consideration and imaging performance optimization techniques in THz quasioptical imaging system optics. Analysis of field and polarization distortion by off-axis parabolic (OAP) mirrors in THz imaging optics shows how distortions are carried in a series of mirrors while guiding the THz beam. While distortions of the beam profile by individual mirrors are not significant, these effects are compounded by a series of mirrors in antisymmetric orientation. It is shown that symmetric orientation of the OAP mirror effectively cancels this distortion to recover the original beam profile. Additionally, symmetric orientation can correct for some geometrical off-focusing due to misalignment. We also demonstrate an alternative method to test for overall system optics alignment by investigating the imaging performance of the tilted target plane. Asymmetric signal profile as a function of the target plane's tilt angle indicates when one or more imaging components are misaligned, giving a preferred tilt direction. Such analysis can offer additional insight into often elusive source device misalignment at an integrated system. Imaging plane tilting characteristics are representative of a 3-D modulation transfer function of the imaging system. A symmetric tilted plane is preferred to optimize imaging performance.

1. Performances of THz cameras with enhanced sensitivity in sub-terahertz region

NASA Astrophysics Data System (ADS)

Oda, Naoki; Ishi, Tsutomu; Kurashina, Seiji; Sudou, Takayuki; Morimoto, Takao; Miyoshi, Masaru; Doi, Kohei; Goto, Hideki; Sasaki, Tokuhito; Isoyama, Goro; Kato, Ryukou; Irizawa, Akinori; Kawase, Keigo

2015-05-01

Uncooled microbolometer-type 640x480 and 320x240 Terahertz (THz) focal plane arrays (FPAs) with enhanced sensitivity in sub-THz region are developed, and incorporated into 640x480 and 320x240 cameras, respectively. The pixel in the THz-FPA has such a structure that an area sensitive to electromagnetic wave is suspended above read-out integrated circuit (ROIC). A thin metallic layer is formed on the top of the sensitive area, while a thick metallic layer is formed on the surface of ROIC. The structure composed of the thin metallic layer and the thick metallic layer behaves as an optical cavity. The THz-FPAs reported in this paper have a modified pixel structure which has several times longer optical-cavity length than NEC's previous pixel does, by forming a thick SiN layer on the ROIC. The extended optical-cavity structure is favorable for detecting electromagnetic wave with lower frequency. Consequently, the Minimum Detectable Power per pixel (MDP) is improved ten times in sub-THz region, especially 0.5-0.6 THz. This paper presents spectral frequency dependences of MDP values for THz-FPA with the modified pixel structure and THz-FPA with the previous pixel structure, using THz free electron laser (FEL) developed by Osaka University. The modification of pixel structure extends high sensitivity region to lower frequency region, such as sub-THz region, and the wider spectral coverage of THz camera surely expands its applicability

2. Probe beam-free detection of terahertz wave by electroluminescence induced by intense THz pulse

NASA Astrophysics Data System (ADS)

Shin, J.; Jin, Z.; Nosaka, Y.; Nakazawa, T.; Kodama, R.

2016-03-01

Recently, a table-top fs laser system can generate MW terahertz (THz) pulse with its electric field higher than 100 kV/cm can be generated by several schemes. Such a strong THz field can directly drive electrons inside various materials. Here, we demonstrated a direct THz electric field detection method by measuring the electroluminescence induced by intense THz pulse inside commonly available light emitting diode. An intense THz wave obtained by the two-color laser scheme was focused onto LED along with an external DC bias to induce luminescence which we found proportional to the amplitude of the incident THz field. The scheme can be useful to realize a low-cost, probe-free THz detection and imaging system.

3. Beam profile and spectral characteristic of THz wave in free space

NASA Astrophysics Data System (ADS)

Zhao, Guozhong; Yang, Kun; Wu, Meng; Wu, Lizhong

2008-12-01

Beam profile and spectral characteristic of terahertz (THz) wave in free space are presented in this paper. The beam width of THz wave at the focus point of parabolic mirror is obtained by means of the narrow-slit measurement. By the spectroscopic imaging, we present the transverse mode distribution of THz beam on the cross-section of focus point. Our experimental results show that the centre wavelength of THz spectra has a distinguished red-shift when it is far away the centre of THz focus point. The spectral range of THz wave far from the focus point is less than that of the centre. This kind of spectral characteristic of THz wave is closely related to the diffraction effect of electromagnetic wave.

4. Revealing plasma oscillation in THz spectrum from laser plasma of molecular jet.

PubMed

Li, Na; Bai, Ya; Miao, Tianshi; Liu, Peng; Li, Ruxin; Xu, Zhizhan

2016-10-03

Contribution of plasma oscillation to the broadband terahertz (THz) emission is revealed by interacting two-color (ω/2ω) laser pulses with a supersonic jet of nitrogen molecules. Temporal and spectral shifts of THz waves are observed as the plasma density varies. The former owes to the changing refractive index of the THz waves, and the latter correlates to the varying plasma frequency. Simulation of considering photocurrents, plasma oscillation and decaying plasma density explains the broadband THz spectrum and the varying THz spectrum. Plasma oscillation only contributes to THz waves at low plasma density owing to negligible plasma absorption. At the longer medium or higher density, the combining effects of plasma oscillation and absorption results in the observed low-frequency broadband THz spectra.

5. Optimizing the sensitivity of porous thin film optical sensors

NASA Astrophysics Data System (ADS)

Mackay, Tom G.

2012-10-01

We considered a porous thin film as a platform for optical sensing. It is envisaged that the porous thin filmbecomes infiltrated by a fluid containing an agent to be sensed. The basis for detection of this agent to besensed is provided by changes in the optical properties of the infiltrated porous thin film. Provided that thepore sizes are much smaller than the wavelengths involved, the infiltrated porous thin film may be regardedas a homogenized composite material. Using the well-established Bruggeman homogenization formalism, thesensitivity of such an optical sensor was investigated theoretically. The sensitivity was considered in relation tothe optical properties of the porous thin film and the infiltrating fluid, the porosity of the thin film, and theshape of the pores. For the case of an isotropic dielectric porous thin film of relative permittivity ɛa and anisotropic dielectric fluid of relative permittivity ɛb, the sensitivity was found to be maximized if: (i) the contrast between ɛa and ɛb was maximized; (ii) mid-range values of porosity were used; (iii) the regime 0 < ɛb < 1 with ɛa » 1 pertained, for example; and (iv) pores which have elongated spheroidal shapes were incorporated.

6. Transmission enhancement of THz pulse through Ag2O-Ag layer detected by THz-TDS

NASA Astrophysics Data System (ADS)

Chen, Hua; Li, Wang

2008-12-01

We used terahertz time-domain spectroscopy (THz-TDS) to probe the enhancement transmission of Ag2O-Ag compound. Using a 500μm- GaAs substrate attaching to the sample, the evanescent wave is coupled to the far field. And the transmitted amplitude is enhanced, corresponding to the frequent shift and spectra broadening.

7. Tunable terahertz multichannel filter based on one-dimensional superconductor-dielectric photonic crystals

SciTech Connect

Liu, Yang; Yi, Lin

2014-12-14

By means of the transfer matrix method, the transmission properties of one-dimensional photonic crystals (PCs) consisting of superconductor and dielectric have been systematically investigated within the terahertz frequency range (0.1–10 THz). It is shown that comb-like resonant peaks in transmission band can be formed without adding any defect layer in superconductor-dielectric PCs, which means that such a one-dimensional periodic structure can serve as a tunable terahertz multichannel filter by using the PCs passband. Furthermore, the influences coming from the period of the structure, the thickness of the components, the permittivity of the dielectric layers, temperature, and the normal conducting electrons on the filtering properties are also numerically investigated.

8. Effective dielectric and elastic properties of nanoporous low-k media

NASA Astrophysics Data System (ADS)

Hermann, H.

2010-07-01

This paper presents a mathematically defined characterization of random porous media including random self-similarity and surface fractality. The initial two-phase structure is transformed into a three-phase system by introducing the internal surface layer as the third phase. Effective medium theories are utilized to calculate macroscopic dielectric and elastic properties. The dependence of both the static dielectric constant and Young's modulus on geometrical parameters is analyzed for different combinations of bulk and interface properties. It is shown that the modification of the properties of the internal surface layer is a promising way to improve the effective constants of the materials. The obtained analytical expressions are also used to determine confined regions in the space of structural parameters where pre-specified property combinations are realized. The results are discussed in terms of possible applications of nanometer-scale porous interlayer dielectrics with an ultralow dielectric constant and sufficient mechanical stiffness for future semiconducting devices.

9. Efficient THZ Source Based on Cascaded Optical Down-Conversion in Orientation-Patterned GaAs Structures

DTIC Science & Technology

2008-11-20

techniques for generating THz radiation [5], none of them provides a THz source which is simultaneously ( i ) compact, (ii) highly efficient, (iii...are very attractive for QPM THz-wave generation because of several appealing properties, namely ( i ) small THz absorption coefficient (smaller by an...with periodically- inverted crystalline orientation were used for QPM THz generation: ( i ) diffusion-bonded GaAs (DB-GaAs) [49], produced by

10. Tunable and reconfigurable THz devices for advanced imaging and adaptive wireless communication

NASA Astrophysics Data System (ADS)

Liu, L.; Shams, M. I. B.; Jiang, Z.; Rahman, S.; Hesler, J. L.; Cheng, L.-J.; Fay, P.

2016-09-01

In this paper, we report on two different approaches that have been explored to realize tunable and reconfigurable THz devices for advanced imaging and adaptive wireless communication. The first approach makes use of electronically tunable varactor diodes. Frequency tunable THz antennas based on this approach have been successfully demonstrated for the first time in G-band, enabling the development of spectroscopic THz detectors and focal-plane imaging arrays. The second approach takes advantages of optical THz spatial modulation based on photo-induced free carriers in semiconductors. Using this approach, high-performance tunable THz modulators/attenuators, reconfigurable masks for THz coded aperture imaging, and photo-induced Fresnel-zone-plate antennas for dynamic THz beam steering and forming have been successfully demonstrated. Our recent study also shows that by employing the so-called mesa array technique, sub-wavelength spatial resolution and higher than 100 dB modulation depth can be achieved, making it possible to develop tunable THz devices (e.g., tunable filters) with performance and versatility far beyond those realized by conventional approaches. On the basis of the above investigation, the prospects of high-speed near-field THz imaging, real-time ultra-sensitive heterodyne imaging and prototype adaptive THz wireless communication links will be discussed.

11. Improved Dielectric Films For Capacitors

NASA Technical Reports Server (NTRS)

Yen, Shiao-Ping S.; Lewis, Carol R.; Cygan, Peter J.; Jow, T. Richard

1994-01-01

Dielectric films made from blends of some commercially available high-dielectric-constant cyanoresins with each other and with cellulose triacetate (CTA) have both high dielectric constants and high breakdown strengths. Dielectric constants as high as 16.2. Films used to produce high-energy-density capacitors.

12. Fabrication of Polyurethane Dielectric Actuators

DTIC Science & Technology

2005-01-01

a summary of a 3 year Technology Investment Fund Project entitled “Dielectric Polymer Actuators for Active/ Passive Vibration Isolation”, which was...completed in March 2005. The purpose of this project was to investigate dielectric polymer materials for potential use in active/ passive vibration...devices and systems based on dielectric polymer actuators. Keywords: dielectric actuators, electroactive polymers , Technology Investment Fund 1

13. THz holography in reflection using a high resolution microbolometer array.

PubMed

Zolliker, Peter; Hack, Erwin

2015-05-04

We demonstrate a digital holographic setup for Terahertz imaging of surfaces in reflection. The set-up is based on a high-power continuous wave (CW) THz laser and a high-resolution (640 × 480 pixel) bolometer detector array. Wave propagation to non-parallel planes is used to reconstruct the object surface that is rotated relative to the detector plane. In addition we implement synthetic aperture methods for resolution enhancement and compare Fourier transform phase retrieval to phase stepping methods. A lateral resolution of 200 μm and a relative phase sensitivity of about 0.4 rad corresponding to a depth resolution of 6 μm are estimated from reconstructed images of two specially prepared test targets, respectively. We highlight the use of digital THz holography for surface profilometry as well as its potential for video-rate imaging.

14. THz imaging of majolica tiles and biological attached marble fragments

NASA Astrophysics Data System (ADS)

Catapano, Ilaria; Soldovieri, Francesco

2016-04-01

Devices exploiting waves in the frequency range from 0.1 THz to 10 THz (corresponding to a free-space wavelength ranging from 30 μm to 3 mm) deserve attention as diagnostic technologies for cultural heritage. THz waves are, indeed, non-ionizing radiations capable of penetrating into non-metallic materials, which are opaque to both visible and infrared waves, without implying long term risks to the molecular stability of the exposed objects and humans. Moreover, THz surveys involve low poewr probing waves, are performed without contact with the object and, thanks to the recent developments, which have allowed the commercialization of compact, flexible and portable systems, maybe performed in loco (i.e. in the place where the artworks are usually located). On the other hand, THz devices can be considered as the youngest among the sensing and imaging electromagnetic techniques and their actual potentialities in terms of characterization of artworks is an ongoing research activity. As a contribution within this context, we have performed time of flight THz imaging [1,2] on ceramic and marble objects. In particular, we surveyed majolica tiles produced by Neapolitan ceramists in the 18th and 19th centuries with the aim to gather information on their structure, constructive technique and conservation state. Moreover, we investigated a Marmo di Candoglia fragment in order to characterize the biological attach affecting it. All the surveys were carried out by using the Fiber-Coupled Terahertz Time Domain System (FICO) developed by Z-Omega and available at the Institute of Electromagnetic Sensing of the Environment (IREA). This system is equipped with fiber optic coupled transmitting and receiving probes and with an automatic positioning system enabling to scan a 150 mm x 150 mm area under a reflection measurement configuration. Based on the obtained results we can state that the use of THz waves allows: - the reconstruction of the object topography; - the geometrical

15. Characterization of a THz CW spectrometer pumped at 1550 nm

NASA Astrophysics Data System (ADS)

Yeo, Woon-Gi; Nahar, Niru K.

2015-07-01

We present an evaluation of a cost-effective THz CW spectrometer pumped at 1550 nm wavelengths with a fixed delay line. To study the spectral competence of the spectrometer, transmission data is obtained for various organic and inorganic samples. Spectral comparisons of the samples are presented by using THz time domain spectroscopy and vector network analyzer (VNA). Despite the capability of highly resolved transmission spectroscopy, our current system reveals the uncertainty in interferometric output data for phase analysis. Here, we identify the effect of fringing space of raw output data toward frequency resolution, phase analysis, and data acquisition time. We also propose the proper delay line setup for phase analysis for this type of spectrometers.

16. Hydration dependence of conformational dielectric relaxation of lysozyme.

PubMed

Knab, Joseph; Chen, Jing-Yin; Markelz, Andrea

2006-04-01

Dielectric response of hen egg white lysozyme is measured in the far infrared (5-65 cm-1, 0.15-1.95 THz, 0.6-8.1 meV) as a function of hydration. The frequency range is associated with collective vibrational modes of protein tertiary structure. The observed frequency dependence of the absorbance is broad and glass-like. For the entire frequency range, there is a slight increase in both the absorbance and index of refraction with increasing hydration for <0.27 h (mass of H2O per unit mass protein). At 0.27 h, the absorbance and index begin to increase more rapidly. This transition corresponds to the point where the first hydration shell is filled. The abrupt increase in dielectric response cannot be fully accounted for by the additional contribution to the dielectric response due to bulk water, suggesting that the protein has not yet achieved its fully hydrated state. The broad, glass-like response suggests that at low hydrations, the low frequency conformational hen egg white lysozyme dynamics can be described by a dielectric relaxation model where the protein relaxes to different local minima in the conformational energy landscape. However, the low frequency complex permittivity does not allow for a pure relaxational mechanism. The data can best be modeled with a single low frequency resonance (nu approximately 120 GHz=4 cm-1) and a single Debye relaxation process (tau approximately .03-.04 ps). Terahertz dielectric response is currently being considered as a possible biosensing technique and the results demonstrate the required hydration control necessary for reliable biosensor applications.

17. Slot-Antenna Coupled Microbolometer Arrays for THz Radiation

DTIC Science & Technology

2000-09-29

properties for 2.5THz-CH 3OH laser radiation were microbolometers ), and each bolometer is connected in investigated at room temperature . The detected voltage...configuration of the infrared frequency region, because of its room - single slot antenna coupled microbolometer . The temperature operation and easy...Vol. X 3 slot antenna coupled microbolometer array and a 3 pp.773-776, Jun.1979. 2. D. F. Filpovic, W. Y. Ali-Ahmad, and G. M. Rebeiz, " Millimeter - two

18. Terahertz (THz) Radar: A Solution for Degraded Visibility Environments (DVE)

DTIC Science & Technology

2016-11-01

THz) frequencies. Preliminary measurements are encouraging and validate the system’s relatively high resolution and ability to tune the frequency...produce useful images at reasonable Size, Weight, and Power (SWaP), lidar’s relatively lower obscurant penetration produces problems in several types of...world’s highest frequency radars (lidar excluded). By operating at higher frequencies relative to MMWs, the ACTI can employ higher gain antennas at

19. Emerging electronic devices for THz sensing and imaging

NASA Astrophysics Data System (ADS)

Fay, P.; Xie, Y.; Zhao, Y.; Jiang, Z.; Rahman, S.; Xing, H.; Sensale-Rodriguez, B.; Liu, L.

2014-09-01

Continuing advances in scaling of conventional semiconductor devices are enabling mainstream electronics to operate in the millimeter-wave through THz regime. At the same time, however, novel devices and device concepts are also emerging to address the key challenges for systems in this frequency range, and may offer performance and functional advantages for future systems. In addition to new devices, advances in integration technology and novel system concepts also promise to provide substantial system-level performance and functionality enhancements. Several emerging devices and device concepts, as well as circuit-level concepts to take advantage of them, are discussed. Based on unconventional semiconductor device structures and operational principles, these devices offer the potential for significantly improved system sensitivity and frequency coverage. When combined in arrays, features such as polarimetric detection and frequency tunability for imaging can be achieved. As examples of emerging devices for millimeter-wave through THz sensing and imaging, heterostructure backward diodes in the InAs/AlSb/GaSb material system and GaN-based plasma-wave high electron mobility transistors (HEMTs) will be discussed. Based on interband tunneling, heterostructure backward diodes offer significantly increased sensitivity and extremely low noise for direct detection applications, and have been demonstrated with cutoff frequencies exceeding 8 THz. The plasma-wave HEMT is an emerging device concept that, by leveraging plasma-wave resonances in the two-dimensional electron gas within the channel of the HEMT, offers the prospect for both tunable narrowband detection as well as low-noise amplification at frequencies well into the THz. These emerging devices are both amenable to direct integration within compact planar radiating structures such as annular slot antennas for realization of polarimetric detection and frequency tuning for spectroscopy and imaging.

20. Correlated Particle Motion and THz Spectral Response of Supercritical Water

NASA Astrophysics Data System (ADS)

Śmiechowski, Maciej; Schran, Christoph; Forbert, Harald; Marx, Dominik

2016-01-01

Molecular dynamics simulations of supercritical water reveal distinctly different distance-dependent modulations of dipolar response and correlations in particle motion compared to ambient conditions. The strongly perturbed H-bond network of water at supercritical conditions allows for considerable translational and rotational freedom of individual molecules. These changes give rise to substantially different infrared spectra and vibrational density of states at THz frequencies for densities above and below the Widom line that separates percolating liquidlike and clustered gaslike supercritical water.

1. Quantum-dot micropillars for parametric THz emission

NASA Astrophysics Data System (ADS)

Mariani, S.; Andronico, A.; Favero, I.; Ducci, S.; Todorov, Y.; Sirtori, C.; Kamp, M.; Claudon, J.; Gérard, J. M.; Wang, T.; Jepsen, P. U.; Leo, G.

2013-01-01

We report on the design, fabrication and optical investigation of AlGaAs microcavities for THz Difference Frequency Generation (DFG) between Whispering Gallery Modes (WGMs), where the pump and DFG wavelengths (λ ≍ 1.3 μm and λ ≍ 75-150 μm, respectively) lie on opposite sides of the Restrahlen band. For the pump modes, we demonstrate CW lasing of quantum-dot layers under electrical injection at room temperature. We control the number of lasing WGMs via vertical notches on the pillars sidewalls, providing a selection mechanism for funneling the power only to the modes contributing to DFG. In parallel with the optimization of the pump lasers and in order to validate design and material parameters before the DFG experiments, we have performed linear measurements on two sets of passive samples. For the telecom range, the micropillars have been integrated with waveguides for distributed coupling and characterized via transmission measurements. In the THz range we have measured reflectivity spectra on 2D arrays of identical cylinders. In both cases, we demonstrate a good agreement between experimental results and simulations. On a more speculative note, we numerically show that etching a hole along the pillar axis can facilitate phase matching, while single-lobe farfield pattern can be obtained for the THz mode by micro-structuring the metallic ground plane around the microcavity. Finally, we suggest a real-time fine-tuning mechanism for the forthcoming active devices.

2. Progress Towards Chirped-Pulse Fourier Transform Thz Spectroscopy

NASA Astrophysics Data System (ADS)

Douglass, Kevin O.; Plusquellic, David F.; Gerecht, Eyal

2010-06-01

New opportunities are provided by the development of higher power THz frequency multiplier sources, the development of a broadband Chirped-Pulse FTMW spectroscopy technique at microwave and mm Wave frequencies, and recently demonstrated heterodyne hot electron bolometer detection technology in the THz frequency region with near quantum noise-limited performance and high spectral resolution. Combining these three technologies and extending the chirped-pulse technique to 0.85 THz enables a host of new applications. NIST is currently pursing applications as a point sensor for greenhouse gases, volatile organic compounds, and potentially human breath. The generation and detection of phase stable chirped pulses at 850 GHz will be demonstrated. A description of the experimental setup and preliminary data will be presented for nitrous oxide. G.G. Brown, B.C. Dian, K.O. Douglass, S.M. Geyer, S. Shipman and B.H. Pate, Rev.Sci.Instrum. 79 (2008) 053103. E. Gerecht, D. Gu, L. You, K.S. Yngvesson, IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES. 56, (2008) 1083.

3. Comparison of objects detection capabilities in LWIR and THz ranges

NASA Astrophysics Data System (ADS)

Kowalski, Marcin; Kastek, Mariusz; Szustakowski, Mieczyslaw

2015-10-01

Multispectral systems for detection of concealed dangerous objects are becoming more popular because of their higher effectiveness compared to mono-spectral systems. So far, the problem of detecting objects hidden under clothing was considered only in the case of airports but it is becoming more important for public places like metro stations, and government buildings. Exploration of new spectral bands as well as development of technology result in introduction of new solutions - both mono and multispectral. It has been proved that objects hidden under clothing can be detected and visualized using terahertz (THz) cameras. However, passive THz cameras still offer too low image resolution for objects recognition. Limited range is another issue of passive imagers. On the other hand new infrared cameras offer sufficient parameters to detect objects covered with fabrics in some conditions, as well as high image quality and big pixel resolutions. The purpose of the studies is to investigate and compare the possibilities of using passive cameras operating in long wavelength infrared (LWIR) and THz spectral ranges for detection of concealed objects. For the purpose of investigations, commercial imagers operating in 6.5-11.7 μm and 250GHz (1.25mm) were used. In the article, we present the measurement setup and the results of measurements in various operating conditions. Theoretical studies of both spectral bands focused on detection of objects with passive imagers are also presented.

4. Mechanical detection of electron spin resonance beyond 1 THz

SciTech Connect

Takahashi, Hideyuki; Ohmichi, Eiji; Ohta, Hitoshi

2015-11-02

We report the cantilever detection of electron spin resonance (ESR) in the terahertz (THz) region. This technique mechanically detects ESR as a change in magnetic torque that acts on the cantilever. The ESR absorption of a tiny single crystal of Co Tutton salt, Co(NH{sub 4}){sub 2}(SO{sub 4}){sub 2}⋅6H{sub 2}O, was observed in frequencies of up to 1.1 THz using a backward travelling wave oscillator as a THz-wave source. This is the highest frequency of mechanical detection of ESR till date. The spectral resolution was evaluated with the ratio of the peak separation to the sum of the half-width at half maximum of two absorption peaks. The highest resolution value of 8.59 ± 0.53 was achieved at 685 GHz, while 2.47 ± 0.01 at 80 GHz. This technique will not only broaden the scope of ESR spectroscopy application but also lead to high-spectral-resolution ESR imaging.

5. Systems Analysis for Thermal Infrared  THz Torch' Applications

NASA Astrophysics Data System (ADS)

Hu, Fangjing; Sun, Jingye; Brindley, Helen E.; Liang, Xiaoxin; Lucyszyn, Stepan

2015-05-01

The  THz Torch' concept was recently introduced by the authors for providing secure wireless communications over short distances within the thermal infrared (10-100 THz). Unlike conventional systems, thermal infrared can exploit front-end thermodynamics with engineered blackbody radiation. For the first time, a detailed power link budget analysis is given for this new form of wireless link. The mathematical modeling of a short end-to-end link is provided, which integrates thermodynamics into conventional signal and noise power analysis. As expected from the Friis formula for noise, it is found that the noise contribution from the pyroelectric detector dominates intrinsic noise. From output signal and noise voltage measurements, experimental values for signal-to-noise ratio (SNR) are obtained and compared with calculated predictions. As with conventional communications systems, it is shown for the first time that the measured SNR and measured bit error rate found with this thermodynamics-based system resembles classical empirical models. Our system analysis can serve as an invaluable tool for the development of thermal infrared systems, accurately characterizing each individual channel and, thus, enables the performance of multi-channel  THz Torch' systems to be optimized.

6. THz Time-Domain Spectroscopy of Complex Interstellar Ice Analogs

NASA Astrophysics Data System (ADS)

Ioppolo, Sergio; McGuire, Brett A.; Allodi, Marco A.; de Vries, Xander; Finneran, Ian; Carroll, Brandon; Blake, Geoffrey

2014-06-01

It is generally accepted that complex organic molecules (COMs) form on the icy surface of interstellar grains. Our ability to identify interstellar complex species in the ices is affected by the limited number of laboratory analogs that can be compared to the huge amount of observational data currently coming from international astronomical facilities, such as the Herschel Space Observatory, SOFIA, and ALMA. We have recently constructed a new THz time-domain spectroscopy system to investigate the spectra of interstellar ice analogs in a range that fully covers the spectral bandwidth of the aforementioned facilities (0.3 - 7.5 THz). The system is coupled to a FT-IR spectrometer to monitor the ices in the mid-IR (4000 - 500 cm-1). This talk focuses on the laboratory investigation of the composition and structure of the bulk phases of interstellar ice analogs (i.e., H2O, CO2, CO, CH3OH, NH3, and CH4) compared to more complex molecules (e.g., HCOOH, CH3COOH, CH3CHO, (CH3)2CO, HCOOCH3, and HCOOC2H5). The ultimate goal of this research project is to provide the scientific community with an extensive THz ice database, which will allow quantitative studies of the ISM, and potentially guide future astronomical observations of species in the solid phase.

7. Cast dielectric composite linear accelerator

DOEpatents

Sanders, David M.; Sampayan, Stephen; Slenes, Kirk; Stoller, H. M.

2009-11-10

A linear accelerator having cast dielectric composite layers integrally formed with conductor electrodes in a solventless fabrication process, with the cast dielectric composite preferably having a nanoparticle filler in an organic polymer such as a thermosetting resin. By incorporating this cast dielectric composite the dielectric constant of critical insulating layers of the transmission lines of the accelerator are increased while simultaneously maintaining high dielectric strengths for the accelerator.

8. Multilayer Dielectric Transmissive Optical Phase Modulator

NASA Technical Reports Server (NTRS)

Keys, Andrew Scott; Fork, Richard Lynn

2004-01-01

A multilayer dielectric device has been fabricated as a prototype of a low-loss, low-distortion, transmissive optical phase modulator that would provide as much as a full cycle of phase change for all frequency components of a transmitted optical pulse over a frequency band as wide as 6.3 THz. Arrays of devices like this one could be an alternative to the arrays of mechanically actuated phase-control optics (adaptive optics) that have heretofore been used to correct for wave-front distortions in highly precise optical systems. Potential applications for these high-speed wave-front-control arrays of devices include agile beam steering, optical communications, optical metrology, optical tracking and targeting, directional optical ranging, and interferometric astronomy. The device concept is based on the same principle as that of band-pass interference filters made of multiple dielectric layers with fractional-wavelength thicknesses, except that here there is an additional focus on obtaining the desired spectral phase profile in addition to the device s spectral transmission profile. The device includes a GaAs substrate, on which there is deposited a stack of GaAs layers alternating with AlAs layers, amounting to a total of 91 layers. The design thicknesses of the layers range from 10 nm to greater than 1 micrometer. The number of layers and the thickness of each layer were chosen in a computational optimization process in which the wavelength dependences of the indices of refraction of GaAs and AlAs were taken into account as the design was iterated to maximize the transmission and minimize the group-velocity dispersion for a wavelength band wide enough to include all significant spectral components of the pulsed optical signal to be phase modulated.

9. Polarimetric scattering behavior of rough dielectric materials at terahertz frequencies

NASA Astrophysics Data System (ADS)

Digiovanni, David Anthony

Technologies in the terahertz region of the spectrum are finding increased usage in areas such as communications, remote sensing, and imaging, For example, driven by the promise of greater data transfer rates, free-space communication that traditionally operate in the radio and microwave bands are being developed at terahertz frequencies. Successful transition of communication systems to higher frequencies, particularly for systems located in indoor or urban environments, will require a thorough understanding of the reflection, transmission, absorption, and scattering behavior of a wide variety of materials and surface types. Scattering properties of rough surfaces have been studied extensively at radio and microwave frequencies, however, such properties have only recently become of interest at higher frequencies. The goal of this thesis was to develop a better understanding of electromagnetic scattering from dielectric rough surfaces at millimeter wavelengths and terahertz frequencies. This goal was achieved by measuring the polarimetric scattering behavior of dielectric materials and comparing the measured data to predictions made by rough surface scattering theory. The dielectric properties and the roughness of the samples were tailored in order to provide a controlled parameter space to investigate. Fully polarimetric radar imagery of the rough surfaces were acquired at 160 GHz, 240 GHz, and 1.55 THz. The backscattering measurements were collected as a function of polarization, incident angle, and frequency. The applicability of various rough surface scattering theories was determined for the different roughness regimes studied.

10. Porous Shape Memory Polymers.

PubMed

Hearon, Keith; Singhal, Pooja; Horn, John; Small, Ward; Olsovsky, Cory; Maitland, Kristen C; Wilson, Thomas S; Maitland, Duncan J

2013-02-04

Porous shape memory polymers (SMPs) include foams, scaffolds, meshes, and other polymeric substrates that possess porous three-dimensional macrostructures. Porous SMPs exhibit active structural and volumetric transformations and have driven investigations in fields ranging from biomedical engineering to aerospace engineering to the clothing industry. The present review article examines recent developments in porous SMPs, with focus given to structural and chemical classification, methods of characterization, and applications. We conclude that the current body of literature presents porous SMPs as highly interesting smart materials with potential for industrial use.

11. Tailored Porous Materials

SciTech Connect

BARTON,THOMAS J.; BULL,LUCY M.; KLEMPERER,WALTER G.; LOY,DOUGLAS A.; MCENANEY,BRIAN; MISONO,MAKOTO; MONSON,PETER A.; PEZ,GUIDO; SCHERER,GEORGE W.; VARTULI,JAMES C.; YAGHI,OMAR M.

1999-11-09

Tailoring of porous materials involves not only chemical synthetic techniques for tailoring microscopic properties such as pore size, pore shape, pore connectivity, and pore surface reactivity, but also materials processing techniques for tailoring the meso- and the macroscopic properties of bulk materials in the form of fibers, thin films and monoliths. These issues are addressed in the context of five specific classes of porous materials: oxide molecular sieves, porous coordination solids, porous carbons, sol-gel derived oxides, and porous heteropolyanion salts. Reviews of these specific areas are preceded by a presentation of background material and review of current theoretical approaches to adsorption phenomena. A concluding section outlines current research needs and opportunities.

12. Porous Shape Memory Polymers

PubMed Central

Hearon, Keith; Singhal, Pooja; Horn, John; Small, Ward; Olsovsky, Cory; Maitland, Kristen C.; Wilson, Thomas S.; Maitland, Duncan J.

2013-01-01

Porous shape memory polymers (SMPs) include foams, scaffolds, meshes, and other polymeric substrates that possess porous three-dimensional macrostructures. Porous SMPs exhibit active structural and volumetric transformations and have driven investigations in fields ranging from biomedical engineering to aerospace engineering to the clothing industry. The present review article examines recent developments in porous SMPs, with focus given to structural and chemical classification, methods of characterization, and applications. We conclude that the current body of literature presents porous SMPs as highly interesting smart materials with potential for industrial use. PMID:23646038

13. THz wave parametric oscillator with a surface-emitted ring-cavity configuration

NASA Astrophysics Data System (ADS)

Yang, Zhen; Wang, Yuye; Xu, Degang; Tang, Longhuang; Xu, Wentao; Duan, Pan; Yan, Chao; Yao, Jianquan

2016-11-01

A surface-emitted ring-cavity terahertz (THz) wave parametric oscillator has been demonstrated for high-energy THz output and fast frequency tuning. Through the special optical design with a Galvano optical scanner and four-mirror ring-cavity structure, a maximum THz output of 12.9 μJ/pulse is achieved at 1.359 THz under the pump pulse energy of 172.8 mJ with the repetition rate of 10 Hz. A further research on the performance of the SE ring-cavity TPO has done to explore more characteristics of THz output. The THz pulse instability and the influence of cavity loss has analyzed. Moreover, the pump depletion rate of the ring-cavity configuration is much lower than the conventional surface-emitted terahertz wave parametric oscillator at the same experimental conditions.

14. High sensitive THz superconducting hot electron bolometer mixers and transition edge sensors

NASA Astrophysics Data System (ADS)

Zhang, W.; Miao, W.; Zhou, K. M.; Guo, X. H.; Zhong, J. Q.; Shi, S. C.

2016-11-01

Terahertz band, which is roughly defined as 0.1 THz to 10 THz, is an interesting frequency region of the electromagnetic spectrum to be fully explored in astronomy. THz observations play key roles in astrophysics and cosmology. High sensitive heterodyne and direct detectors are the main tools for the detection of molecular spectral lines and fine atomic structure spectral lines, which are very important tracers for probing the physical and chemical properties and dynamic processes of objects such as star and planetary systems. China is planning to build an THz telescope at Dome A, Antarctica, a unique site for ground-based THz observations. We are developing THz superconducting hot electron bolometer (HEB) mixers and transition edge sensors (TES), which are quantum limited and back-ground limited detectors, respectively. Here we first introduce the working principles of superconducting HEB and TES, and then mainly present the results achieved at Purple mountain Observatory.

15. Strongly Enhanced THz Emission caused by Localized Surface Charges in Semiconducting Germanium Nanowires

PubMed Central

Lee, Woo-Jung; Ma, Jin Won; Bae, Jung Min; Jeong, Kwang-Sik; Cho, Mann-Ho; Kang, Chul; Wi, Jung-Sub

2013-01-01

A principal cause of THz emission in semiconductor nanostructures is deeply involved with geometry, which stimulates the utilization of indirect bandgap semiconductors for THz applications. To date, applications for optoelectronic devices, such as emitters and detectors, using THz radiation have focused only on direct bandgap materials. This paper reports the first observation of strongly enhanced THz emission from Germanium nanowires (Ge NWs). The origin of THz generation from Ge NWs can be interpreted using two terms: high photoexcited electron-hole carriers (Δn) and strong built-in electric field (Eb) at the wire surface based on the relation . The first is related to the extensive surface area needed to trigger an irradiated photon due to high aspect ratio. The second corresponds to the variation of Fermi-level determined by confined surface charges. Moreover, the carrier dynamics of optically excited electrons and holes give rise to phonon emission according to the THz region. PMID:23760467

16. All-dielectric periodic terajet waveguide using an array of coupled cuboids

SciTech Connect

Minin, I. V. Minin, O. V.; Pacheco-Peña, V. Beruete, M.

2015-06-22

In this paper, the recently proposed technique to produce photonic jets (terajets at terahertz (THz) frequencies) using 3D dielectric cuboids is applied in the design of a mesoscale cuboid-chain waveguide. The chains are basically designed with several dielectric cubes with side λ{sub 0} placed periodically along the axial z-axis and separated by an air-gap. Based on this, a systematic study of the focusing properties and wave guiding of this chain is performed when the air-gap between the dielectric cubes is changed from 0.25λ{sub 0} to 3λ{sub 0} with the best performance achieved at 2.5λ{sub 0}. An analysis when losses are included in the cubes is also done, demonstrating a robust performance. Finally, the wave guiding is experimentally demonstrated at sub-THz frequencies with a good agreement with numerical results. The simulation results of focusing and transport properties are carried out using Finite Integration Technique. The results here presented may be scaled to any frequency ranges such as millimeter, sub-millimeter, and optical frequencies.

17. Pattern formation in dielectric barrier discharges with different dielectric materials

SciTech Connect

Dong, L. F.; Fan, W. L.; Wang, S.; Ji, Y. F.; Liu, Z. W.; Chen, Q.

2011-03-15

The influence of dielectric material on the bifurcation and spatiotemporal dynamics of the patterns in dielectric barrier discharge in argon/air at atmospheric pressure is studied. It is found that pattern bifurcation sequences are different with different dielectric materials. The spatiotemporal dynamics of the hexagonal pattern in dielectric barrier discharge depends on the dielectric material. The hexagon pattern with glass dielectric is an interleaving of two rectangular sublattices appearing at different moments. The hexagon pattern with quartz dielectric is composed of one set of hexagonal lattice discharging twice in one half cycle of the applied voltage, one is at the rising edge and the other at the falling edge. It results in that the accumulation of wall charges in individual microdischarges in a hexagon pattern with quartz dielectric is greater than that with glass dielectric, which is in agreement with the electron density measurement by Stark broadening of Ar I 696.54 nm.

18. High birefringence, low loss terahertz photonic crystal fibres with zero dispersion at 0.3 THz

NASA Astrophysics Data System (ADS)

Yin, Guo-Bing; Li, Shu-Guang; Wang, Xiao-Yan; Liu, Shuo

2011-09-01

A terahertz photonic crystal fibre (THz-PCF) is designed for terahertz wave propagation. The dispersion property and model birefringence are studied by employing the finite element method. The simulation result reveals the changing patten of dispersion parameter versus the geometry. The influence of the large frequency band of terahertz on birefringence is also discussed. The design of low loss, high birefringence THz-PCFs with zero dispersion frequency at 0.3 THz is presented.

19. DOE-NSF-NIH Workshop on Opportunities in THz Science, February 12-14, 2004

SciTech Connect

Sherwin, M.A.; Bucksbaum, P.H.; Schmuttenmaer, C. A.; Allen, J.; Biedron, S.; Carr, L.; Chamberlain, M.; Crowe, T.; DeLucia, F.; Hu, Q.; Jones, B.; Noordham, B.; Norris, T.; Orenstein, J.; Unterrainer, K.; Van der Meer, L.; Wilke, I.; Williams, G.; Zhang, X.-C.; Cheville, A.; Markelz, A.; Parks, B.; Plancken, P.; Shan, J.; Austin, B.; Basov, D.; Citrin, D.; Grundfest, W.; Heinz, T.; Kono, J.; Mittleman, D.; Siegel, P.; Taylor, T.; Jones, B.; Markelz, A.; Martin, M.; Nelson, K.; Smith, T.; Williams, G.; Allen, M.; Averitt, R.; Brunel, L.; Heilweil, T.; Heyman, J.; Jepsen, P.; Kaind, R.; Leemans, W.; Mihaly, L.; Rangan, C.; Tom, H.; Wallace, V.; Zimdars, D.

2004-02-14

This is the report of the Workshop on Opportunities in THz Science, held on February 12-14, 2004 in Arlington, VA. This workshop brought together researchers who use or produce THz radiation for physics, chemistry, biology, medicine, and materials science to discuss new research opportunities and common resource needs. The charge from the sponsors of the workshop was to focus on basic science questions within these disciplines that have and can be answered using THz radiation.

20. Complete presentation of the Gouy phase shift with the THz digital holography.

PubMed

Wang, Xinke; Sun, Wenfeng; Cui, Ye; Ye, Jiasheng; Feng, Shengfei; Zhang, Yan

2013-01-28

Three dimensional information of the Gouy phase shift in a converging spherical terahertz (THz) beam is directly observed by using a THz balanced electro-optic holographic imaging system. The major properties of the Gouy phase shift are presented, including the longitudinal and transverse distributions, relationships with the frequency and the f-number, influence on the THz polarization. The imaging technique supplies an accurate and comprehensive measurement method for observing and understanding the Gouy phase shift.

1. Tunable, Room Temperature CMOS-Compatible THz Emitters Based on Nonlinear Mixing in Microdisk Resonators

NASA Astrophysics Data System (ADS)

Sinha, Raju; Karabiyik, Mustafa; Ahmadivand, Arash; Al-Amin, Chowdhury; Vabbina, Phani Kiran; Shur, Michael; Pala, Nezih

2016-03-01

We propose and investigate in detail a novel tunable, compact, room temperature terahertz (THz) emitter using individual microdisk resonators for both optical and THz waves with the capability of radiating THz field in 0.5-10 THz range with tuning frequency resolution of 0.05 THz. Enhanced THz generation is achieved by employing a nonlinear optical disk resonator with a high value of second-order nonlinearity ( χ (2)) in order to facilitate the difference-frequency generation (DFG) via nonlinear mixing with the choice of two appropriate input infrared optical waves. Efficient coupling of infrared waves from bus to the nonlinear disk is ensured by satisfying critical coupling condition. Phase matching condition for efficient DFG process is also met by employing modal phase matching technique. Our simulations show that THz output power can be reached up to milliwatt (mW) level with high optical to THz conversion efficiency. The proposed source is Silicon on Insulator (SoI) technology compatible enabling the monolithic integration with Si complementary metal-oxide-semiconductor (CMOS) electronics including plasmonic THz detectors.

2. Pore-size dependent THz absorption of nano-confined water.

PubMed

Sun, Chi-Kuang; You, Borwen; Huang, Yu-Ru; Liu, Kao-Hsiang; Sato, Shusaku; Irisawa, Akiyoshi; Imamura, Motoki; Mou, Chung-Yuan

2015-06-15

We performed a THz absorption spectroscopy study on liquid water confined in mesoporous silica materials, MCM-41-S-18 and MCM-41-S-21, of two different pore sizes at room temperatures. We found that stronger confinement with a smaller pore size causes reduced THz absorption, indicating reduced water mobility due to confinement. Combined with recent theoretical studies showing that the microscopic structure of water inside the nanopores can be separated into a core water region and an interfacial water region, our spectroscopy analysis further reveals a bulk-water-like THz absorption behavior in the core water region and a solid-like THz absorption behavior in the interfacial water region.

3. High Terahertz Absorbing Nanoscale Metal Films for Fabrication of Micromechanical Bi-material THz Sensors

DTIC Science & Technology

2010-06-01

the vacuum cell , when the THz source is off. After the THz illumination, through the lens and the wrapped object, the respective pixels which absorb...placed into the vacuum cell , when the THz source is off. After the THz illumination, through the lens and the wrapped object, the respective pixels...Refraction Index of Silicon Oxide layer % n4=2.05; n5=1.46; n6=2.05; n7=1.46; n8=2.05; n9 =1.46; n10=2.05; n11=1.46; n12=(1-i

4. THz generation from elliptically-focused two-color laser pulses at 1 kHz

NASA Astrophysics Data System (ADS)

Yoo, Yungjun; Kuk, Donghoon; Zhong, Zheqiang; Kim, Ki-Yong

2017-01-01

We have generated high-power terahertz (THz) radiation by elliptical focusing of two-color femtosecond laser pulses in air at a 1-kHz repetition rate. Elliptical focusing produces a 2-dimensional plasma sheet, emitting two diverging THz radiation lobes in the far field. Such radiation is collimated and refocused by a combination of cylindrical and off-axis parabolic mirrors. Here the distances between the 2-D plasma sheet, cylindrical mirror, and off-axis parabolic mirror are carefully adjusted to minimize the THz spot size at the refocus. The refocused THz field strength is estimated by measuring the THz energy, beam spot size, and waveform. Here an uncooled microbolometer camera with real-time lock-in imaging is used to monitor and measure the focused THz beam profiles with a high signal-to-noise ratio at a broad range of THz (1 40 THz) frequencies. High-pressure gas (N2 and Ar) jets puffed in air are also tested as laser targets to boost the output THz energy even further. This material is based upon work supported by the Air Force Office of Scientific Research under Award Number FA9550-16-1-0163.

5. Experimental 0.22 THz Stepped Frequency Radar System for ISAR Imaging

NASA Astrophysics Data System (ADS)

Liang, Mei Yan; Zhang, Cun Lin; Zhao, Ran; Zhao, Yue Jin

2014-09-01

High resolution inverse synthetic aperture radar (ISAR) imaging is demonstrated by using a 0.22 THz stepped-frequency (SF) imaging radar system. The synthesis bandwidth of the terahertz (THz) SF radar is 12 GHz, which are beneficial for high resolution imaging. The resolution of ISAR image can reach centimeter-scale with the use of Range-Doppler algorithm (RDA). Results indicate that high resolution ISAR imaging is realized by using 0.22THz SF radar coupled with turntable scanning, which can provide foundations for further research on high-resolution radar image in the THz band.

6. Characterization of dielectric properties of nanocellulose from wood and algae for electrical insulator applications.

PubMed

Le Bras, David; Strømme, Maria; Mihranyan, Albert

2015-05-07

Cellulose is one of the oldest electrically insulating materials used in oil-filled high-power transformers and cables. However, reports on the dielectric properties of nanocellulose for electrical insulator applications are scarce. The aim of this study was to characterize the dielectric properties of two nanocellulose types from wood, viz., nanofibrillated cellulose (NFC), and algae, viz., Cladophora cellulose, for electrical insulator applications. The cellulose materials were characterized with X-ray diffraction, nitrogen gas and moisture sorption isotherms, helium pycnometry, mechanical testing, and dielectric spectroscopy at various relative humidities. The algae nanocellulose sample was more crystalline and had a lower moisture sorption capacity at low and moderate relative humidities, compared to NFC. On the other hand, it was much more porous, which resulted in lower strength and higher dielectric loss than for NFC. It is concluded that the solid-state properties of nanocellulose may have a substantial impact on the dielectric properties of electrical insulator applications.

7. PREFACE: Dielectrics 2011

NASA Astrophysics Data System (ADS)

Vaughan, Alun; Lewin, Paul

2011-08-01

In 2011, the biennial meeting of the Dielectrics Group of the IOP, Dielectrics 2011, was held for the first time in a number of years at the University of Kent at Canterbury. This conference represents the most recent in a long standing series that can trace its roots back to a two-day meeting that was held in the spring of 1968 at Gregynog Hall of the University of Wales. In the intervening 43 years, this series of meetings has addressed many topics, including dielectric relaxation, high field phenomena, biomaterials and even molecular electronics, and has been held at many different venues within the UK. However, in the early 1990s, a regular venue was established at the University of Kent at Canterbury and, it this respect, this year's conference can be considered as "Dielectrics coming home". The format for the 2011 meeting followed that established at Dielectrics 2009, in breaking away from the concept of a strongly themed event that held sway during the mid 2000s. Rather, we again adopted a general, inclusive approach that was based upon four broad technical areas: Theme 1: Insulation/HV Materials Theme 2: Dielectric Spectroscopy Theme 3: Modelling Dielectric Response Theme 4: Functional Materials The result was a highly successful conference that attracted more than 60 delegates from eight countries, giving the event a truly international flavour, and which included both regular and new attendees; it was particularly pleasing to see the number of early career researchers at the meeting. Consequently, the organizing committee would like to thank our colleagues at the IOP, the invited speakers, our sponsors and all the delegates for making the event such a success. Finally, we look forward to convening again in 2013, when we will be returning to The University of Reading. Prof Alun Vaughan and Prof Paul Lewin, Editors

8. Experimental study on the dielectric properties of polyacrylate dielectric elastomer

NASA Astrophysics Data System (ADS)

Qiang, Junhua; Chen, Hualing; Li, Bo

2012-02-01

The dielectric constant of elastomeric dielectric material is an essential physical parameter, whose value may affect the electromechanical deformation of a dielectric elastomer actuator. Since the dielectric constant is influenced by several external factors as reported before, and no certain value has been confirmed to our knowledge, in the present paper, on the basis of systematical comparison of recent past literature, we conducted extensive works on the measurement of dielectric properties of VHB films, involving five influencing factors: prestretch (both equal and unequal biaxial), electrical frequency, electrode material, stress relaxation time and temperature. Experimental results directly show that the dielectric response changes according to these factors, based on which we investigate the significance of each factor, especially the interaction of two external conditions on the dielectric constant of deformable dielectric, by presenting a physical picture of the mechanism of polarization.

9. Porous organic molecules

NASA Astrophysics Data System (ADS)

Holst, James R.; Trewin, Abbie; Cooper, Andrew I.

2010-11-01

Most synthetic materials that show molecular-scale porosity consist of one-, two- or three-dimensional networks. Porous metal-organic frameworks in particular have attracted a lot of recent attention. By contrast, discrete molecules tend to pack efficiently in the solid state, leaving as little empty space as possible, which leads to non-porous materials. This Perspective discusses recent developments with discrete organic molecules that are porous in the solid state. Such molecules, which may be either crystalline or amorphous, can be categorized as either intrinsically porous (containing permanent covalent cavities) or extrinsically porous (inefficiently packed). We focus on the possible advantages of organic molecules over inorganic or hybrid systems in terms of molecular solubility, choice of components and functionalities, and structural mobility and responsiveness in non-covalent extended solids. We also highlight the potential for 'undiscovered' porous systems among the large number of cage-like organic molecules that are already known.

10. Plasma damage effects on low-k porous organosilicate glass

SciTech Connect

Ren, H.; Shohet, J. L.; Antonelli, G. A.; Nishi, Y.

2010-11-15

Damage induced in low-k porous organosilicate glass (SiCOH) dielectric films by exposure to an electron cyclotron resonance (ECR) plasma was investigated. The effects of charged-particle bombardment and vacuum ultraviolet radiation were separated. Flux measurements showed that the ECR plasma has a greater photon flux in the vacuum ultraviolet (VUV) range than in the UV range. Damage was measured by examining the surface potential and capacitance-voltage characteristics after exposure. It was found that during argon ECR plasma processing, 75% of the charge accumulation comes from ions at the surface, while 25% of the charge accumulation occurs from charge trapped within the bulk of the dielectric film. The charge accumulation can be modified by changing the bias voltage of the wafer chuck. UV exposure was shown to repair both sources of damage. Fourier transform infrared (FTIR) spectroscopy results showed no significant change except for Si-(CH{sub 3}){sub x} bonds. It was found that both charged-particle bombardment and radiation from the ECR plasma damage these bonds. Ellipsometric measurements showed that both the dielectric thickness and the dielectric constant changed during plasma exposure. In addition, both plasma-induced swelling and UV-exposure shrinking effects were observed. The plasma-induced swelling occurs at the surface of the dielectric without changing the porosity of the dielectric, while UV-induced shrinking changes the porosity significantly.

11. Dielectric relaxation and polar phonon softening in relaxor ferroelectric PbMg1/3Ta2/3O3

NASA Astrophysics Data System (ADS)

Kamba, S.; Nuzhnyy, D.; Veljko, S.; Bovtun, V.; Petzelt, J.; Wang, Y. L.; Setter, N.; Levoska, J.; Tyunina, M.; Macutkevic, J.; Banys, J.

2007-10-01

Relaxor ferroelectric PbMg1/3Ta2/3O3 ceramics and thin films were investigated by means of broad-band dielectric, time-domain terahertz (THz), and Fourier-transform infrared (IR) spectroscopy in the frequency range 100 Hz-90 THz at temperatures 100-490 K; the THz and IR spectra were studied from 20 to 900 K. A diffused and strongly temperature dependent peak in the complex permittivity is caused by a dielectric relaxation due to the dynamics of polar clusters. The relaxation appears below the Burns temperature Td in the THz range; it slows down on cooling through the microwave and MHz range and anomalously broadens. The shortest and longest relaxation times of the distribution of relaxation times follow Arrhenius and Vogel-Fulcher laws, respectively. The degree of the B-site order has only a small influence on the parameters of the dielectric relaxation and almost no influence on the phonon parameters. Below Tm≅180 K the distribution of relaxation frequencies becomes broader than our experimental spectral range, and frequency independent dielectric losses develop below 100 GHz in the spectra. Although the macroscopic crystal structure is cubic, IR spectra give evidence about the lower local symmetry, which can be assigned to the presence of the polar clusters below Td. Infrared spectra above Td still reveal more modes than predicted by selection rules in the paraelectric phase of the Fm3¯m space group so that we suggest selection rules which take into account chemical inhomogeneity in the β″-perovskite sublattice.

12. Influence of porosity on electrical properties of low-k dielectrics irradiated with vacuum-ultraviolet radiation

NASA Astrophysics Data System (ADS)

Choudhury, F. A.; Nguyen, H. M.; Baklanov, M. R.; de Marneffe, J. F.; Li, W.; Pei, D.; Benjamin, D. I.; Zheng, H.; King, S. W.; Lin, Y.-H.; Fung, H.-S.; Chen, C.-C.; Nishi, Y.; Shohet, J. L.

2016-09-01

During plasma processing, low-k dielectrics are exposed to high levels of vacuum ultraviolet (VUV) radiation emitted from the plasma. The porous structure of these materials makes them more sensitive to modification because of their low density and consequently deep penetration of active species into the film. Here, we investigate the changes to electrical properties of porous low-k dielectrics as a function of porosity after VUV irradiation. Organosilicate low-k films of porosities between 30% and 50% were exposed to synchrotron VUV radiation at 8 eV with a fluence of approximately 5 × 1014 photons/cm2. Capacitance-voltage measurements showed an increase in the dielectric constant along with a flat-band voltage shift. FTIR results show methyl depletion as well as water uptake after VUV treatment. These show that deterioration of the electrical properties after VUV exposure and the degree of damage are found to be higher for the more porous films.

13. Thz Spectroscopy of 12CH^+, 13CH^+, and 12CD^+

NASA Astrophysics Data System (ADS)

Yu, Shanshan; Drouin, Brian; Pearson, John; Amano, Takayoshi

2015-06-01

In 1937, Dunham detected a couple of unidentified lines in near-UV, and later Douglas and Herzberg identified them based on their laboratory observations to be low-J electronic transitions of CH^+. The electronic spectra, in particular the A^1Π-X^1σ^+ band, have been investigated extensively. On the other hand, the pure rotational transitions have not been studied so extensively. Only the lowest rotational transition, J=1-0, was observed in the laboratory for the normal species, 13CH^+, and CD^+. Based on the laboratory frequency, CH^+ was detected in star forming regions with the Hershel space observatory. Cernicharo et al identified pure rotational transitions from J=2-1 to J=6-5 in the far-infrared region in the ISO spectrum of the planetary nebula NGC 7027. The ISO spectra, however, were of low-resolution, so high-resolution spectroscopic observation is highly desirable. In this presentation, we have extended the measurements to higher-J lines up to 2 THz. For production of CH^+, an extended negative glow discharge in a gas mixture of CH_4 (˜ 0.5 mTorr) diluted in He (˜ 60 mTorr) was used. The optimum discharge current was about 15 mA and the axial magnetic filed to 160 Gauss was applied up. The discharge cell was cooled down to liquid nitrogen temperature. Several frequency multiplier chains, developed at JPL and purchased from Virginia Diodes, were used as THz radiation sources. New THz measurements are not only useful for providing better characterization of spectroscopic properties but also will serve as starting point for astronomical observations. T. Dunham, Publ. Astron. Soc. Pac., 49,~26 (1937) A. E. Douglas and G. Herzberg, Ap. J. 94,~381 (1941) T. Amano, Ap.J.Lett., 716, L1 (2010) T. Amano, J. Chem. Phys., 133, 244305 (2010) J. Cernicharo et al., Ap. J. Lett., 483, L65 (1997)

14. Ultra low-loss hybrid core porous fiber for broadband applications.

PubMed

Islam, Md Saiful; Sultana, Jakeya; Atai, Javid; Abbott, Derek; Rana, Sohel; Islam, Mohammad Rakibul

2017-02-01

In this paper, we present the design and analysis of a novel hybrid porous core octagonal lattice photonic crystal fiber for terahertz (THz) wave guidance. The numerical analysis is performed using a full-vector finite element method (FEM) that shows that 80% of bulk absorption material loss of cyclic olefin copolymer (COC), commercially known as TOPAS can be reduced at a core diameter of 350 μm. The obtained effective material loss (EML) is as low as 0.04  cm-1 at an operating frequency of 1 THz with a core porosity of 81%. Moreover, the proposed photonic crystal fiber also exhibits comparatively higher core power fraction, lower confinement loss, higher effective mode area, and an ultra-flattened dispersion profile with single mode propagation. This fiber can be readily fabricated using capillary stacking and sol-gel techniques, and it can be used for broadband terahertz applications.

15. Dielectric Constant of Suspensions

NASA Astrophysics Data System (ADS)

Mendelson, Kenneth S.; Ackmann, James J.

1997-03-01

We have used a finite element method to calculate the dielectric constant of a cubic array of spheres. Extensive calculations support preliminary conclusions reported previously (K. Mendelson and J. Ackmann, Bull. Am. Phys. Soc. 41), 657 (1996).. At frequencies below 100 kHz the real part of the dielectric constant (ɛ') shows oscillations as a function of the volume fraction of suspension. These oscillations disappear at low conductivities of the suspending fluid. Measurements of the dielectric constant (J. Ackmann, et al., Ann. Biomed. Eng. 24), 58 (1996). (H. Fricke and H. Curtis, J. Phys. Chem. 41), 729 (1937). are not sufficiently sensitive to show oscillations but appear to be consistent with the theoretical results.

16. Superdirective dielectric nanoantennas

NASA Astrophysics Data System (ADS)

Krasnok, Alexander E.; Simovski, Constantin R.; Belov, Pavel A.; Kivshar, Yuri S.

2014-06-01

We introduce the novel concept of superdirective nanoantennas based on the excitation of higher-order magnetic multipole moments in subwavelength dielectric nanoparticles. Our superdirective nanoantenna is a small Si nanosphere containing a notch, and is excited by a dipole located within the notch. In addition to extraordinary directivity, this nanoantenna demonstrates efficient radiation steering at the nanoscale, resulting from the subwavelength sensitivity of the beam radiation direction to variation of the source position inside the notch. We compare our dielectric nanoantenna with a plasmonic nanoantenna of similar geometry, and reveal that the nanoantenna's high directivity in the regime of transmission is not associated with strong localization of near fields in the regime of reception. Likewise, the absence of hot spots inside the nanoantenna leads to low dissipation in the radiation regime, so that our dielectric nanoantenna has significantly smaller losses and high radiation efficiency of up to 70%.

17. Dielectric assist accelerating structure

NASA Astrophysics Data System (ADS)

Satoh, D.; Yoshida, M.; Hayashizaki, N.

2016-01-01

A higher-order TM02 n mode accelerating structure is proposed based on a novel concept of dielectric loaded rf cavities. This accelerating structure consists of ultralow-loss dielectric cylinders and disks with irises which are periodically arranged in a metallic enclosure. Unlike conventional dielectric loaded accelerating structures, most of the rf power is stored in the vacuum space near the beam axis, leading to a significant reduction of the wall loss, much lower than that of conventional normal-conducting linac structures. This allows us to realize an extremely high quality factor and a very high shunt impedance at room temperature. A simulation of a 5 cell prototype design with an existing alumina ceramic indicates an unloaded quality factor of the accelerating mode over 120 000 and a shunt impedance exceeding 650 M Ω /m at room temperature.

18. PREFACE: Dielectrics 2013

NASA Astrophysics Data System (ADS)

Hadjiloucas, Sillas; Blackburn, John

2013-11-01

This volume records the 42nd Dielectrics Group Proceedings of the Dielectrics Conference that took place at the University of Reading UK from 10-12 April 2013. The meeting is part of the biennial Dielectrics series of the Dielectrics Group, and formerly Dielectrics Society, and is organised by the Institute of Physics. The conference proceedings showcase some of the diversity and activity of the Dielectrics community worldwide, and bring together contributions from academics and industrial researchers with a diverse background and experiences from the Physics, Chemistry and Engineering communities. It is interesting to note some continuing themes such as Insulation/HV Materials, Dielectric Spectroscopy, Dielectric Measurement Techniques and Ferroelectric materials have a growing importance across a range of technologically important areas from the Energy sector to Materials research, Semiconductor and Electronics industries, and Metrology. We would like to thank all of our colleagues and friends in the Dielectrics community who have supported this event by contributing manuscripts and participating in the event. The conference has provided excellent networking opportunities for all delegates. Our thanks go also to our theme chairs: Dr Stephen Dodd (University of Leicester) on Insulation/HV Materials, Professor Darryl Almond (University of Bath) on Dielectric Spectroscopy, Dr John Blackburn (NPL) on Dielectric Measurement Techniques and Professor Anthony R West (University of Sheffield) on Ferroelectric Materials. We would also like to thank the other members of the Technical Programme Committee for their support, and refereeing the submitted manuscripts. Our community would also like to wish a full recovery to our plenary speaker Prof John Fothergill (City University London) who was unexpectedly unable to give his talk as well as thank Professor Alun Vaughan for stepping in and giving an excellent plenary lecture in his place at such very short notice. We are also

19. Controlling birefringence in dielectrics

NASA Astrophysics Data System (ADS)

Danner, Aaron J.; Tyc, Tomáš; Leonhardt, Ulf

2011-06-01

Birefringence, from the very essence of the word itself, refers to the splitting of light rays into two parts. In natural birefringent materials, this splitting is a beautiful phenomenon, resulting in the perception of a double image. In optical metamaterials, birefringence is often an unwanted side effect of forcing a device designed through transformation optics to operate in dielectrics. One polarization is usually implemented in dielectrics, and the other is sacrificed. Here we show, with techniques beyond transformation optics, that this need not be the case, that both polarizations can be controlled to perform useful tasks in dielectrics, and that rays, at all incident angles, can even follow different trajectories through a device and emerge together as if the birefringence did not exist at all. A number of examples are shown, including a combination Maxwell fisheye/Luneburg lens that performs a useful task and is achievable with current fabrication materials.

20. Structure and performance of dielectric films based on self-assembled nanocrystals with a high dielectric constant

NASA Astrophysics Data System (ADS)

Huang, Limin; Liu, Shuangyi; Van Tassell, Barry J.; Liu, Xiaohua; Byro, Andrew; Zhang, Henan; Leland, Eli S.; Akins, Daniel L.; Steingart, Daniel A.; Li, Jackie; O'Brien, Stephen

2013-10-01

Self-assembled films built from nanoparticles with a high dielectric constant are attractive as a foundation for new dielectric media with increased efficiency and range of operation, due to the ability to exploit nanofabrication techniques and emergent electrical properties originating from the nanoscale. However, because the building block is a discrete one-dimensional unit, it becomes a challenge to capture potential enhancements in dielectric performance in two or three dimensions, frequently due to surface effects or the presence of discontinuities. This is a recurring theme in nanoparticle film technology when applied to the realm of thin film semiconductor and device electronics. We present the use of chemically synthesized (Ba,Sr)TiO3 nanocrystals, and a novel deposition-polymerization technique, as a means to fabricate the dielectric layer. The effective dielectric constant of the film is tunable according to nanoparticle size, and effective film dielectric constants of up to 34 are enabled. Wide area and multilayer dielectrics of up to 8 cm2 and 190 nF are reported, for which the building block is an 8 nm nanocrystal. We describe models for assessing dielectric performance, and distinct methods for improving the dielectric constant of a nanocrystal thin film. The approach relies on evaporatively driven assembly of perovskite nanocrystals with uniform size distributions in a tunable 7-30 nm size range, coupled with the use of low molecular weight monomer/polymer precursor chemistry that can infiltrate the porous nanocrystal thin film network post assembly. The intercrystal void space (low k dielectric volume fraction) is minimized, while simultaneously promoting intercrystal connectivity and maximizing volume fraction of the high k dielectric component. Furfuryl alcohol, which has good affinity to the surface of (Ba,Sr)TiO3 nanocrystals and miscibility with a range of solvents, is demonstrated to be ideal for the production of nanocomposites. The

1. Real-time nondestructive imaging with THz waves

NASA Astrophysics Data System (ADS)

Zhang, LiangLiang; Karpowicz, Nick; Zhang, CunLin; Zhao, YueJin; Zhang, XiCheng

2008-03-01

We present a real-time imaging measurement in the terahertz (THz) frequency region. The dynamic subtraction technique is used to reduce long-term optical background drift. The reflective images of two targets, a Nikon camera's lens cap and a plastic toy gun, are obtained. For the lens cap, the image data were processed to be false-color images. For the toy gun, we show that even under an optically opaque canvas bag, a clear terahertz image is obtained. It is shown that terahertz real-time imaging can be used to nondestructively detect concealed objects.

2. Detection of covered materials in the TDS-THz setup

NASA Astrophysics Data System (ADS)

Palka, Norbert

2013-05-01

We report on a new method for extracting the characteristic features of covered materials, including Hexogen, in the range 0.5-1.8 THz. This time domain spectroscopy-based technique takes into account only part of the signal reflected from a covered sample, and analyzes it by Fourier transform. The obtained power spectrum has distinctive peaks that correspond to peaks measured in the transmission configuration and can be applied for further identification. We showed results obtained for the samples of hexogen, lactose, and tartaric acid covered with commonly used packaging materials such as plastic, foil, paper and cotton.

3. Electron beam induced THz emissions from nanotube array

NASA Astrophysics Data System (ADS)

Kumar, Ashok; Kumar, Pawan

2016-10-01

A new scheme of terahertz radiation generation by passing an ultrashort electron bunch over a planar array of nanotube/nanorod across their lengths is proposed and analyzed. The beam pulse exerts a repulsive impulse on the free electron cylinder of each nanorod and displaces them with respect to ion cylinder. After the passage of the pulse, the electron cylinders oscillate at their natural frequency ω p / √{ 2 } (where ω p is the plasma frequency of electrons in each carbon nanotube) acting as phased array dipole antennae, emitting THz radiation.

4. Low Noise 1.2 THz SIS Receiver

NASA Technical Reports Server (NTRS)

Karpov, A.; Miller, D.; Rice, F.; Zmuidzinas, J.; Stern, J. A.; Bumble, B.; LeDuc, H. G.

2001-01-01

We present the development of a low noise superconductor insulator superconductor (SIS) mixer for the 1.1 - 1.25 THz heterodyne receiver of FIRST space radiotelescope. The quasi-optical SIS mixer has two NbTiN/AlN/Nb junctions with critical current density 30 kA/sq cm. The individual junction area is close to 0.65 square micrometers. The SIS junctions are coupled to the optical input beam through a planar double slot antenna and a Si hyperhemispherical lens. The minimum DSB receiver noise temperature is 650 K, about 12 hv/k.

5. Modulating sub-THz radiation with current in superconducting metamaterial.

PubMed

Savinov, V; Fedotov, V A; Anlage, S M; de Groot, P A J; Zheludev, N I

2012-12-14

We show that subterahertz transmission of the superconducting metamaterial, an interlinked two-dimensional network of subwavelength resonators connected by a continuous superconducting wire loop, can be dynamically modulated by passing electrical current through it. We have identified the main mechanisms of modulation that correspond to the suppression of the superconductivity in the network by magnetic field and heat dissipation. Using the metamaterial fabricated from thin niobium film, we were able to demonstrate a transmission modulation depth of up to 45% and a bandwidth of at least 100 kHz. The demonstrated approach may be implemented with other superconducting materials at frequencies below the superconducting gap in the THz and subterahertz bands.

6. All-optoelectronic continuous wave THz imaging for biomedical applications.

PubMed

Siebert, Karsten J; Löffler, Torsten; Quast, Holger; Thomson, Mark; Bauer, Tobias; Leonhardt, Rainer; Czasch, Stephanie; Roskos, Hartmut G

2002-11-07

We present an all-optoelectronic THz imaging system for ex vivo biomedical applications based on photomixing of two continuous-wave laser beams using photoconductive antennas. The application of hyperboloidal lenses is discussed. They allow for f-numbers less than 1/2 permitting better focusing and higher spatial resolution compared to off-axis paraboloidal mirrors whose f-numbers for practical reasons must be larger than 1/2. For a specific histological sample, an analysis of image noise is discussed.

7. Low THz spectroscopy of some widely used explosives

NASA Astrophysics Data System (ADS)

Globus, Tatiana; Gelmont, Boris; Khromova, Tatyana

2010-04-01

We investigated resonance spectroscopic features from several widely used explosives materials including RDX and PETN in the low THz range with the goal of understanding the mechanism of interaction between radiation and material in the form of solid films, gels and dilute solutions (suspensions). FTIR spectroscopy was used to measure spectra in transmission and reflection modes. We demonstrated that very small amount of material with a simple sample preparation technique can be used still providing very accurate results. Spectral features are specific not only for main ingredients but for modifications with different plasticizers. The consistency of results for different amount of material was observed. Computational modeling confirmed the lowest frequency modes.

8. THz metamaterials made of phonon-polariton materials

NASA Astrophysics Data System (ADS)

Kafesaki, M.; Basharin, A. A.; Economou, E. N.; Soukoulis, C. M.

2014-08-01

In this paper, we demonstrate numerically various phenomena and possibilities that can be realized in THz metamaterials made of phonon-polariton materials. Such phenomena include hyperbolic dispersion relation, subwavelength imaging using backward propagation and backward radiation, total transmission and subwavelength guiding exploiting Mie-resonant scattering in permittivity near zero host, and toroidal dipolar response. The systems that we use to demonstrate most of these phenomena are two-dimensional periodic systems of μm-scale rods in a host, where both rods and host are made of polaritonic alkali-halide materials.

9. Millimeter-wave/THz FMCW radar techniques for sensing applications

NASA Astrophysics Data System (ADS)

Mirando, D. Amal; Higgins, Michael D.; Wang, Fenggui; Petkie, Douglas T.

2016-10-01

Millimeter-wave and terahertz continuous-wave radar systems have been used to measure physiological signatures for biometric applications and for a variety of non-destructive evaluation applications, such as the detection of defects in materials. Sensing strategies for the simplest homodyne systems, such as a Michelson Interferometer, can be enhanced by using Frequency Modulated Continuous Wave (FMCW) techniques. This allows multiple objects or surfaces to be range resolved while monitoring the phase of the signal in a particular range bin. We will discuss the latest developments in several studies aimed at demonstrating how FMCW techniques can enhance mmW/THz sensing applications.

10. Corneal tissue water content mapping with THz imaging: preliminary clinical results (Conference Presentation)

NASA Astrophysics Data System (ADS)

Sung, Shijun; Bajwa, Neha; Deng, Sophie X.; Taylor, Zachary; Grundfest, Warren

2016-03-01

Well-regulated corneal water content is critical for ocular health and function and can be adversely affected by a number of diseases and injuries. Current clinical practice limits detection of unhealthy corneal water content levels to central corneal thickness measurements performed by ultrasound or optical coherence tomography. Trends revealing increasing or decreasing corneal thickness are fair indicators of corneal water content by individual measurements are highly inaccurate due to the poorly understood relationship between corneal thickness and natural physiologic variation. Recently the utility of THz imaging to accuarately measure corneal water content has been explored on with rabbit models. Preliminary experiments revealed that contact with dielectric windows confounded imaging data and made it nearly impossible to deconvolve thickness variations due to contact from thickness variations due to water content variation. A follow up study with a new optical design allowed the acquisition of rabbit data and the results suggest that the observed, time varying contrast was due entirely to the water dynamics of the cornea. This paper presents the first ever in vivo images of human cornea. Five volunteers with healthy cornea were recruited and their eyes were imaged three times over the course of a few minutes with our novel imaging system. Noticeable changes in corneal reflectivity were observed and attributed to the drying of the tear film. The results suggest that clinically compatible, non-contact corneal imaging is feasible and indicate that signal acquired from non-contact imaging of the cornea is a complicated coupling of stromal water content and tear film.

11. Thermally switchable dielectrics

DOEpatents

Dirk, Shawn M.; Johnson, Ross S.

2013-04-30

Precursor polymers to conjugated polymers, such as poly(phenylene vinylene), poly(poly(thiophene vinylene), poly(aniline vinylene), and poly(pyrrole vinylene), can be used as thermally switchable capacitor dielectrics that fail at a specific temperature due to the non-conjugated precursor polymer irreversibly switching from an insulator to the conjugated polymer, which serves as a bleed resistor. The precursor polymer is a good dielectric until it reaches a specific temperature determined by the stability of the leaving groups. Conjugation of the polymer backbone at high temperature effectively disables the capacitor, providing a built-in safety mechanism for electronic devices.

12. A dielectric affinity microbiosensor

NASA Astrophysics Data System (ADS)

Huang, Xian; Li, Siqi; Schultz, Jerome S.; Wang, Qian; Lin, Qiao

2010-01-01

We present an affinity biosensing approach that exploits changes in dielectric properties of a polymer due to its specific, reversible binding with an analyte. The approach is demonstrated using a microsensor comprising a pair of thin-film capacitive electrodes sandwiching a solution of poly(acrylamide-ran-3-acrylamidophenylboronic acid), a synthetic polymer with specific affinity to glucose. Binding with glucose induces changes in the permittivity of the polymer, which can be measured capacitively for specific glucose detection, as confirmed by experimental results at physiologically relevant concentrations. The dielectric affinity biosensing approach holds the potential for practical applications such as long-term continuous glucose monitoring.

13. Multilayer dielectric diffraction gratings

DOEpatents

Perry, Michael D.; Britten, Jerald A.; Nguyen, Hoang T.; Boyd, Robert; Shore, Bruce W.

1999-01-01

The design and fabrication of dielectric grating structures with high diffraction efficiency used in reflection or transmission is described. By forming a multilayer structure of alternating index dielectric materials and placing a grating structure on top of the multilayer, a diffraction grating of adjustable efficiency, and variable optical bandwidth can be obtained. Diffraction efficiency into the first order in reflection varying between 1 and 98 percent has been achieved by controlling the design of the multilayer and the depth, shape, and material comprising the grooves of the grating structure. Methods for fabricating these gratings without the use of ion etching techniques are described.

14. Multilayer dielectric diffraction gratings

DOEpatents

Perry, M.D.; Britten, J.A.; Nguyen, H.T.; Boyd, R.; Shore, B.W.

1999-05-25

The design and fabrication of dielectric grating structures with high diffraction efficiency used in reflection or transmission is described. By forming a multilayer structure of alternating index dielectric materials and placing a grating structure on top of the multilayer, a diffraction grating of adjustable efficiency, and variable optical bandwidth can be obtained. Diffraction efficiency into the first order in reflection varying between 1 and 98 percent has been achieved by controlling the design of the multilayer and the depth, shape, and material comprising the grooves of the grating structure. Methods for fabricating these gratings without the use of ion etching techniques are described. 7 figs.

15. Controlling of strong tunable THz emission with optimal incommensurate multi-color laser field

NASA Astrophysics Data System (ADS)

Zhang, Lei; Wang, Guo-Li; Zhao, Song-Feng; Zhou, Xiao-Xin

2017-02-01

Based on the photocurrent model, we study terahertz (THz) emission from argon plasmas induced by incommensurate-frequency two- and three-color laser fields. In order to enhance the THz radiation at an arbitrary frequency efficiently, a genetic algorithm is applied to search for the optimum laser parameters. For the longer two-color field, our optimizations show that the THz tunability is mainly determined by two laser frequencies, which approximately meets the law Ω = 2ω1-ω2. However, for the shorter laser pulse, the tunability of the THz wave with lower frequency also depends on the relative phase. To control the tunable THz emission, we systematically investigated how to generate the stronger THz wave with the shorter spectrum width using the optimal synthesized waveform. We found that the THz intensity can be enhanced by about an order with three-color field compared with the two-color cases. We also show that the tunable single ultrashort THz pulses can be obtained by using an optimized 50-fs two-color pulse.

16. Study of the possibility of diagnostic cataract in the THz range

NASA Astrophysics Data System (ADS)

Ezerskaya, A.; Smolyanskaya, O.; Goncharenko, A.; Geyko, I.

2013-03-01

It was revealed correlation between the optical density of the lens's nucleus in terahertz range with its density, determined according to the L. Buratti classification. Consolidation of the lens fibers caused by senile cataract, increases the reflectivity of the lens in the THz range. The temporal structure of reflected THz signals allows to determine the spatial distribution of density in the lens.

17. SYNCHROTRON RADIATION, FREE ELECTRON LASER, APPLICATION OF NUCLEAR TECHNOLOGY, ETC.: Study on the characteristics of linac based THz light source

NASA Astrophysics Data System (ADS)

Zhu, Xiong-Wei; Wang, Shu-Hong; Chen, Sen-Yu

2009-10-01

There are many methods based on linac for THz radiation production. As one of the options for the Beijing Advanced Light, an ERL test facility is proposed for THz radiation. In this test facility, there are 4 kinds of methods to produce THz radiation: coherent synchrotron radiation (CSR), synchrotron radiation (SR), low gain FEL oscillator, and high gain SASE FEL. In this paper, we study the characteristics of the 4 kinds of THz light sources.

18. Subwavelength InSb-based Slot wavguides for THz transport: concept and practical implementations

PubMed Central

Ma, Youqiao; Zhou, Jun; Pištora, Jaromír; Eldlio, Mohamed; Nguyen-Huu, Nghia; Maeda, Hiroshi; Wu, Qiang; Cada, Michael

2016-01-01

Seeking better surface plasmon polariton (SPP) waveguides is of critical importance to construct the frequency-agile terahertz (THz) front-end circuits. We propose and investigate here a new class of semiconductor-based slot plasmonic waveguides for subwavelength THz transport. Optimizations of the key geometrical parameters demonstrate its better guiding properties for simultaneous realization of long propagation lengths (up to several millimeters) and ultra-tight mode confinement (~λ2/530) in the THz spectral range. The feasibility of the waveguide for compact THz components is also studied to lay the foundations for its practical implementations. Importantly, the waveguide is compatible with the current complementary metal-oxide-semiconductor (CMOS) fabrication technique. We believe the proposed waveguide configuration could offer a potential for developing a CMOS plasmonic platform and can be designed into various components for future integrated THz circuits (ITCs). PMID:27924939

19. THz radiation as a bunch diagnostic forlaser-wakefield-accelerated electron bunches

SciTech Connect

van Tilborg, J.; Schroeder, C.B.; Filip, C.V.; Toth, Cs.; Geddes,C.G.R.; Fubiani, G.; Esarey, E.; Leemans, W.P.

2006-02-15

Experimental results are reported from two measurementtechniques (semiconductor switching and electro-optic sampling) thatallow temporal characterization of electron bunches produced by alaser-driven plasma-based accelerator. As femtosecond electron bunchesexit the plasma-vacuum interface, coherent transition radiation (at THzfrequencies) is emitted. Measuring the properties of this radiationallows characterization of the electron bunches. Theoretical work on theemission mechanism is represented, including a model that calculates theTHz waveform from a given bunch profile. It is found that the spectrum ofthe THz pulse is coherent up to the 200 mu m thick crystal (ZnTe)detection limit of 4 THz, which corresponds to the production of sub-50fs (root-mean-square) electron bunch structure. The measurementsdemonstrate both the shot-to-shot stability of bunch parameters that arecritical to THz emission (such as total charge and bunch length), as wellas femtosecond synchrotron between bunch, THz pulse, and laserbeam.

20. THz Plasma Diagnostics: an evolution from FIR and Millimeter waves historical applications

NASA Astrophysics Data System (ADS)

Bombarda, F.; Doria, A.; Galatola Teka, G.; Giovenale, E.; Zerbini, M.

2016-08-01

Extremely broadband (100 GHz-30 THz) single cycle THz pulses are routinely generated with femtosecond laser for Time Domain Spectroscopy applications (TDS). The wide frequency range has an unquestionable diagnostic potential for Tokamak plasmas and not surprisingly THz TDS finds a natural field of application in this area, which is an evolution of the FIR and millimeter waves diagnostics, where ENEA Frascati holds historical expertise. By illuminating the plasma with a THz beam, phase, intensity and polarization of both reflected and transmitted beams can be detected, devising a single diagnostic instrument capable of measuring multiple plasma parameters. We will describe and discuss the laboratory work now in progress to realise a tailored THz-TDS spectrometer with design parameters optimised for the requirements of Tokamak plasmas and the tests of optical fibers and quasioptical couplers to optimise access to plasma. ENEA Frascati and the Photonics group of Physics Dept. of Oxford University are collaborating on this subject [1].

1. THz Acoustic Spectroscopy by using Double Quantum Wells and Ultrafast Optical Spectroscopy

PubMed Central

Wei, Fan Jun; Yeh, Yu-Hsiang; Sheu, Jinn-Kong; Lin, Kung-Hsuan

2016-01-01

GaN is a pivotal material for acoustic transducers and acoustic spectroscopy in the THz regime, but its THz phonon properties have not been experimentally and comprehensively studied. In this report, we demonstrate how to use double quantum wells as a THz acoustic transducer for measuring generated acoustic phonons and deriving a broadband acoustic spectrum with continuous frequencies. We experimentally investigated the sub-THz frequency dependence of acoustic attenuation (i.e., phonon mean-free paths) in GaN, in addition to its physical origins such as anharmonic scattering, defect scattering, and boundary scattering. A new upper limit of attenuation caused by anharmonic scattering, which is lower than previously reported values, was obtained. Our results should be noteworthy for THz acoustic spectroscopy and for gaining a fundamental understanding of heat conduction. PMID:27346494

2. OPTIMIZATION AND SINGLE-SHOT CHARACTERIZATION OF ULTRASHORT THz PULSES FROM A LASER WAKEFIELD ACCELERATOR

SciTech Connect

Plateau, G. R.; Matlis, N. H.; van Tilborg, J.; Geddes, C. G. R.; Toth, Cs.; Schroeder, C. B.; Leemans, W. P.

2009-05-04

We present spatiotemporal characterization of J-class ultrashort THz pulses generated from a laser wakefield accelerator (LWFA). Accelerated electrons, resulting from the interaction of a high-intensity laser pulse with a plasma, emit high-intensity THz pulses as coherent transition radiation. Such high peak-power THz pulses, suitable for high-field (MV/cm) pump-probe experiments, also provide a non-invasive bunch-length diagnostic and thus feedback for the accelerator. The characterization of the THz pulses includes energy measurement using a Golay cell, 2D sign-resolved electro-optic measurement and single-shot spatiotemporal electric-field distribution retrieval using a new technique, coined temporal electric-field cross-Correlation (TEX). All three techniques corroborate THz pulses of 5 muJ, with peak fields of 100's of kV/cm and ~;;0:4 ps rms duration.

3. Subwavelength InSb-based Slot wavguides for THz transport: concept and practical implementations

NASA Astrophysics Data System (ADS)

Ma, Youqiao; Zhou, Jun; Pištora, Jaromír; Eldlio, Mohamed; Nguyen-Huu, Nghia; Maeda, Hiroshi; Wu, Qiang; Cada, Michael

2016-12-01

Seeking better surface plasmon polariton (SPP) waveguides is of critical importance to construct the frequency-agile terahertz (THz) front-end circuits. We propose and investigate here a new class of semiconductor-based slot plasmonic waveguides for subwavelength THz transport. Optimizations of the key geometrical parameters demonstrate its better guiding properties for simultaneous realization of long propagation lengths (up to several millimeters) and ultra-tight mode confinement (~λ2/530) in the THz spectral range. The feasibility of the waveguide for compact THz components is also studied to lay the foundations for its practical implementations. Importantly, the waveguide is compatible with the current complementary metal-oxide-semiconductor (CMOS) fabrication technique. We believe the proposed waveguide configuration could offer a potential for developing a CMOS plasmonic platform and can be designed into various components for future integrated THz circuits (ITCs).

4. High power and spectral purity continuous-wave photonic THz source tunable from 1 to 4.5 THz for nonlinear molecular spectroscopy

NASA Astrophysics Data System (ADS)

Kiessling, J.; Breunig, I.; Schunemann, P. G.; Buse, K.; Vodopyanov, K. L.

2013-10-01

We report a diffraction-limited photonic terahertz (THz) source with linewidth <10 MHz that can be used for nonlinear THz studies in the continuous wave (CW) regime with uninterrupted tunability in a broad range of THz frequencies. THz output is produced in orientation-patterned (OP) gallium arsenide (GaAs) via intracavity frequency mixing between the two closely spaced resonating signal and idler waves of an optical parametric oscillator (OPO) operating near λ = 2 μm. The doubly resonant type II OPO is based on a periodically poled lithium niobate (PPLN) pumped by a single-frequency Yb:YAG disc laser at 1030 nm. We take advantage of the enhancement of both optical fields inside a high-finesse OPO cavity: with 10 W of 1030 nm pump, 100 W of intracavity power near 2 μm was attained with GaAs inside cavity. This allows dramatic improvement in terms of generated THz power, as compared to the state-of-the art CW methods. We achieved >25 μW of single-frequency tunable CW THz output power scalable to >1 mW with proper choice of pump laser wavelength.

5. Instantaneous charge and dielectric response to terahertz pulse excitation in TTF-CA

NASA Astrophysics Data System (ADS)

Gomi, Hiroki; Yamagishi, Naoto; Mase, Tomohito; Inagaki, Takeshi J.; Takahashi, Akira

2017-03-01

We present the results of exact numerical calculations of the dielectric properties of tetrathiafulvalene-p -chloranil (TTF-CA) using the extended Hubbard model. The electronic polarization P¯el of the ionic ground state is obtained by directly calculating the adiabatic flow of current. The direction of P¯el is opposite to polarization P¯ion owing to ionic displacement, and | P¯el| is much larger than | P¯ion| , showing that, in the ionic phase, TTF-CA is an electric ferroelectric. Furthermore, we numerically calculate the dynamics induced by THz pulse excitation. In the ionic phase, there exists an almost exact linear relationship between Δ ρ (t ) and E (t ) , and between Δ Pel(t ) and E (t ) in the realistic range of the excitation magnitude, where Δ ρ (t ) [Δ Pel(t ) ] is the charge transfer (electric polarization) variation induced by the THz pulse and E (t ) is the electric field of the pulse at time t . The absolute value of Δ ρ (t ) in the neutral phase is much smaller than that in the ionic phase. These results are consistent with those of experiments and originate from the adiabatic nature of the THz pulse excited state.

6. THz Microscopy of Anisotropy and Correlated Motions in Protein Crystals

NASA Astrophysics Data System (ADS)

Niessen, Katherine; Acbas, Gheorghe; Snell, Edward; Markelz, Andrea

2013-03-01

We introduce a new technique, Crystal Anisotropy Terahertz Microscopy (CATM) which can directly measure correlated intra-molecular protein vibrations. The terahertz (THz) frequency range (5-100 cm-1) corresponds to global correlated protein motions, proposed to be essential to protein function [1, 2]. CATM accesses these motions by removal of the relaxational background of the solvent and residue side chain librational motions. We demonstrate narrowband features in the anisotropic absorbance for hen egg-white lysozyme (HEWL) single crystals as well as HEWL with triacetylglucosamine (HEWL-3NAG) inhibitor single crystals. The most prominent features for the HEWL crystals appear at 45 cm-1, 69 cm-1, and 78 cm-1 and the strength of the absorption varies with crystal orientation relative to the THz polarization. Calculations show similar anisotropic features, suggesting specific correlated mode identification is possible. 1. Hammes-Schiffer, S. and S.J. Benkovic, Relating Protein Motion to Catalysis. Annu. Rev. Biochem., 2006. 75: p. 519-41. 2. Henzler-Wildman, K.A., et al., Intrinsic motions along an enzymatic reaction trajectory. Nature, 2007. 450(7171): p. 838-U13. This work supported by NSF MRI2 grant DBI295998.

7. Identification of THz absorption spectra of chemicals using neural networks

NASA Astrophysics Data System (ADS)

Shen, Jingling; Jia, Yan; Liang, Meiyan; Chen, Sijia

2007-09-01

Absorption spectra in the range from 0.2 to 2.6 THz of chemicals such as illicit drugs and antibiotics obtaining from Terahertz time-domain spectroscopy technique were identified successfully by artificial neural networks. Back Propagation (BP) and Self-Organizing Feature Map (SOM) were investigated to do the identification or classification, respectively. Three-layer BP neural networks were employed to identify absorption spectra of nine illicit drugs and six antibiotics. The spectra of the chemicals were used to train a BP neural network and then the absorption spectra measured in different times were identified by the trained BP neural network. The average identification rate of 76% was achieved. SOM neural networks, another important neural network which sorts input vectors by their similarity, was used to sort 60 absorption spectra from 6 illicit drugs. The whole network was trained by setting a 20×20 and a 16×16 grid, and both of them had given satisfied clustering results. These results indicate that it is feasible to apply BP and SOM neural networks model in the field of THz spectra identification.

8. Nonlinear THz response of metallic armchair graphene nanoribbon superlattices

NASA Astrophysics Data System (ADS)

Wang, Yichao; Andersen, David R.

2016-11-01

We study the third order THz nonlinear response of metallic armchair graphene nanoribbon superlattices in the presence of an elliptically-polarized excitation field using the time dependent perturbation theory. For a one-dimensional Kronig-Penney potential of infinite length, the nonlinear response can be described perturbatively by a low energy \\mathbf{k}\\centerdot \\mathbf{p} N-photon coupling model. Remarkably, as shown by Burset et al the energy dispersion of the metallic band in the direction parallel to the superlattice wavevector is independent of the applied superlattice potential while the energy dispersion in the direction perpendicular to the superlattice wavevector depends strongly on the superlattice parameters. As a result, we predict novel behavior for the nonlinear response of single layer metallic acGNR superlattices to an applied elliptically-polarized electric field. Our work shows that the superlattice potential, periodicity, Fermi level, excitation field polarization state, and temperature all play a significant role in the resulting THz nonlinear conductances.

9. Nanoklystron: A Monolithic Tube Approach to THz Power Generation

NASA Technical Reports Server (NTRS)

Siegel, Peter H.; Fung, Andy; Manohara, Harish; Xu, Jimmy; Chang, Baohe

2001-01-01

The authors propose a new approach to THz power generation: the nanoklystron. Utilizing silicon micromachining techniques, the design and fabrication concept of a monolithic THz vacuum-tube reflex-klystron source is described. The nanoklystron employs a separately fabricated cathode structure composed of densely packed carbon nanotube field emitters and an add-in repeller. The nanotube cathode is expected to increase the current density, extend the cathode life and decrease the required oscillation voltage to values below 100 V. The excitation cavity is based on ridged-waveguide and differs from the conventional cylindrical re-entrant structures found in lower frequency klystrons. A quasi-static field analysis of the cavity and output coupling structure show excellent control of the quality factor and desired field distribution. Output power is expected to occur through an iris coupled matched rectangular waveguide and integrated pyramidal feed horn. The entire circuit is designed so as to be formed monolithically from two thermocompression bonded silicon wafers processed using deep reactive ion etching (DRIE) techniques. To expedite prototyping, a 600 GHz mechanically machined structure has been designed and is in fabrication. A complete numeric analysis of the nanoklystron circuit, including the electron beam dynamics has just gotten underway. Separate evaluation of the nanotube cathodes is also ongoing. The authors will describe the progress to date as well as plans for the immediate implementation and testing of nanoklystron prototypes at 640 and 1250 GHz.

10. Thermally triggered phononic gaps in liquids at THz scale

SciTech Connect

Bolmatov, Dima; Zhernenkov, Mikhail; Zavyalov, Dmitry; Stoupin, Stanislav; Cunsolo, Alessandro; Cai, Yong Q.

2016-01-14

In this study we present inelastic X-ray scattering experiments in a diamond anvil cell and molecular dynamic simulations to investigate the behavior of phononic excitations in liquid Ar. The spectra calculated using molecular dynamics were found to be in a good agreement with the experimental data. Furthermore, we observe that, upon temperature increases, a low-frequency transverse phononic gap emerges while high-frequency propagating modes become evanescent at the THz scale. The effect of strong localization of a longitudinal phononic mode in the supercritical phase is observed for the first time. The evidence for the high-frequency transverse phononic gap due to the transition from an oscillatory to a ballistic dynamic regimes of motion is presented and supported by molecular dynamics simulations. This transition takes place across the Frenkel line thermodynamic limit which demarcates compressed liquid and non-compressed fluid domains on the phase diagram and is supported by calculations within the Green-Kubo phenomenological formalism. These results are crucial to advance the development of novel terahertz thermal devices, phononic lenses, mirrors, and other THz metamaterials.

11. Theory of THz harmonic generation in semiconductor superlattices (Conference Presentation)

NASA Astrophysics Data System (ADS)

Pereira, Mauro F.; Winge, David O.; Wacker, Andreas

2016-10-01

Superlattices are artificial structures with a wide range of applications and open possibilities for controlling and study transport and optical [M.F. Pereira Jr., Phys. Rev. B 52, (1995)] properties of semiconductors. In this work, we start from the full Nonequilibrium Greens Functions approach [A. Wacker et a, IEEE Journal of Sel. Top. in Quantum Electron.,19 1200611, (2013),T. Schmielau and M.F. Pereira, Appl. Phys. Lett. 95 231111, (2009)] to obtain Voltage-Current curves and compare them with experiments. By adjusting the numerical solutions of the corresponding Dyson equations to a simple model, analytical solutions are given for the nonlinear response of a biased superlattice under sub-THz radiation. The frequency multiplication process leading to multiple harmonicgeneration is described. This hybrid approach leads to predictive simulations and may have important application for a new generation of devices where the superlattices are used as both sources and detectors and may be particular useful for high resolution transient spectroscopy [A.A. Yablokov et at, IEEE Transactions on THz Science and Technology 5, 845 (2015)].

12. Microfabrication of SU-8 Fresnel lenses for THz imaging

NASA Astrophysics Data System (ADS)

Hajji, M.; Pan, Y.; Hammler, J.; Zeze, D.; Balocco, C.; Gallant, A. J.

2016-02-01

Free space focusing of terahertz light is normally achieved through the use of bulky parabolic mirrors. Alternatively, for focusing onto a substrate or sample, polished high resistivity silicon lenses are commonly used. This paper presents the design, fabrication and testing of an alternative approach, based on Fresnel microlenses which have been optimised for use in the terahertz region. The microlenses are fabricated using layers of SU-8 photoresist and conventional UV photolithography. The lens design approach presented here provides a low cost, mass production ready alternative to silicon lenses. Fresnel lenses can have a large numerical aperture and a short focal length and are well suited for use in terahertz imaging systems. The focal point of the demonstrated Fresnel microlens has been calculated to be approximately 5 mm at 1 THz using a commercial FDTD solver, Lumerical. Characterization of the microlenses by VNA (Vector Network Analyzer) operating in the frequency range of 750 GHz to 1.1 THz is presented and discussed. The measured focal length using the VNA approach corresponds well to the values calculated using the FDTD solver and demonstrates effective focusing from highly compact lenses.

13. Thermally triggered phononic gaps in liquids at THz scale

DOE PAGES

Bolmatov, Dima; Zhernenkov, Mikhail; Zavyalov, Dmitry; ...

2016-01-14

In this study we present inelastic X-ray scattering experiments in a diamond anvil cell and molecular dynamic simulations to investigate the behavior of phononic excitations in liquid Ar. The spectra calculated using molecular dynamics were found to be in a good agreement with the experimental data. Furthermore, we observe that, upon temperature increases, a low-frequency transverse phononic gap emerges while high-frequency propagating modes become evanescent at the THz scale. The effect of strong localization of a longitudinal phononic mode in the supercritical phase is observed for the first time. The evidence for the high-frequency transverse phononic gap due to themore » transition from an oscillatory to a ballistic dynamic regimes of motion is presented and supported by molecular dynamics simulations. This transition takes place across the Frenkel line thermodynamic limit which demarcates compressed liquid and non-compressed fluid domains on the phase diagram and is supported by calculations within the Green-Kubo phenomenological formalism. These results are crucial to advance the development of novel terahertz thermal devices, phononic lenses, mirrors, and other THz metamaterials.« less

14. Thermally triggered phononic gaps in liquids at THz scale

PubMed Central

Bolmatov, Dima; Zhernenkov, Mikhail; Zav’yalov, Dmitry; Stoupin, Stanislav; Cunsolo, Alessandro; Cai, Yong Q.

2016-01-01

In this paper we present inelastic X-ray scattering experiments in a diamond anvil cell and molecular dynamic simulations to investigate the behavior of phononic excitations in liquid Ar. The spectra calculated using molecular dynamics were found to be in a good agreement with the experimental data. Furthermore, we observe that, upon temperature increases, a low-frequency transverse phononic gap emerges while high-frequency propagating modes become evanescent at the THz scale. The effect of strong localization of a longitudinal phononic mode in the supercritical phase is observed for the first time. The evidence for the high-frequency transverse phononic gap due to the transition from an oscillatory to a ballistic dynamic regimes of motion is presented and supported by molecular dynamics simulations. This transition takes place across the Frenkel line thermodynamic limit which demarcates compressed liquid and non-compressed fluid domains on the phase diagram and is supported by calculations within the Green-Kubo phenomenological formalism. These results are crucial to advance the development of novel terahertz thermal devices, phononic lenses, mirrors, and other THz metamaterials. PMID:26763899

15. Hierarchical Porous Structures

SciTech Connect

Grote, Christopher John

2016-06-07

Materials Design is often at the forefront of technological innovation. While there has always been a push to generate increasingly low density materials, such as aero or hydrogels, more recently the idea of bicontinuous structures has gone more into play. This review will cover some of the methods and applications for generating both porous, and hierarchically porous structures.

16. Ventilation of porous media

DOEpatents

Neeper, D.A.

1994-02-22

Methods are presented for distributing gases throughout the interstices of porous materials and removing volatile substances from the interstices of porous materials. Continuous oscillation of pressures and flows results in increased penetration of the interstices by flowing gases and increased transport of gaseous components out of the interstices. The invention is particularly useful in soil vapor extraction. 10 figures.

17. Ventilation of porous media

DOEpatents

Neeper, Donald A.

1994-01-01

Methods for distributing gases throughout the interstices of porous materials and removing volatile substances from the interstices of porous materials. Continuous oscillation of pressures and flows results in increased penetration of the interstices by flowing gases and increased transport of gaseous components out of the interstices. The invention is particularly useful in soil vapor extraction.

18. A novel, all-dielectric, microwave plasma generator towards development of plasma metamaterials

NASA Astrophysics Data System (ADS)

Cohick, Zane; Luo, Wei; Perini, Steven; Baker, Amanda; Wolfe, Douglas; Lanagan, Michael

2016-11-01

A proof of concept for a microwave microplasma generator that consists of a halved dielectric resonator is presented. The generator functions via leaking electric fields of the resonant modes — TE01δ and HEM12δ modes are explored. Computational results illustrate the electric fields, whereas the stability of resonance and coupling are studied experimentally. Finally, a working device is presented. This generator promises potentially wireless and low-loss operation. This device may find relevance in plasma metamaterials; each resonator may generate the plasma structures necessary to manipulate electromagnetic radiation. In particular, the all-dielectric nature of the generator will allow low-loss interaction with high-frequency (GHz-THz) waves.

19. Electromagnetic scattering from dielectric surfaces at millimeter wave and terahertz frequencies

NASA Astrophysics Data System (ADS)

DiGiovanni, D. A.; Gatesman, A. J.; Giles, R. H.; Goyette, T. M.; Nixon, W. E.

2015-05-01

With the demand for larger bandwidths and faster data speeds, wireless communication systems are expanding into the millimeter wave and terahertz region of the electromagnetic spectrum. Successful transition to higher frequencies, particularly for systems located in urban or indoor environments, will require a thorough understanding of the reflection, transmission, absorption, and scattering of a wide variety of materials. For this study, the co-polarization and crosspolarization backscattering coefficients of several dielectrics were measured in compact radar ranges operating from 160 GHz to 1.55 THz. These structures consisted of dielectric disks with various rough surfaces. The backscattering measurements of these disks were compared as a function of polarization, incident angle, roughness, and frequency.

20. Porous photonic crystal external cavity laser biosensor

NASA Astrophysics Data System (ADS)

Huang, Qinglan; Peh, Jessie; Hergenrother, Paul J.; Cunningham, Brian T.

2016-08-01

We report the design, fabrication, and testing of a photonic crystal (PC) biosensor structure that incorporates a porous high refractive index TiO2 dielectric film that enables immobilization of capture proteins within an enhanced surface-area volume that spatially overlaps with the regions of resonant electromagnetic fields where biomolecular binding can produce the greatest shifts in photonic crystal resonant wavelength. Despite the nanoscale porosity of the sensor structure, the PC slab exhibits narrowband and high efficiency resonant reflection, enabling the structure to serve as a wavelength-tunable element of an external cavity laser. In the context of sensing small molecule interactions with much larger immobilized proteins, we demonstrate that the porous structure provides 3.7× larger biosensor signals than an equivalent nonporous structure, while the external cavity laser (ECL) detection method provides capability for sensing picometer-scale shifts in the PC resonant wavelength caused by small molecule binding. The porous ECL achieves a record high figure of merit for label-free optical biosensors.

1. Porous photonic crystal external cavity laser biosensor.

PubMed

Huang, Qinglan; Peh, Jessie; Hergenrother, Paul J; Cunningham, Brian T

2016-08-15

We report the design, fabrication, and testing of a photonic crystal (PC) biosensor structure that incorporates a porous high refractive index TiO2 dielectric film that enables immobilization of capture proteins within an enhanced surface-area volume that spatially overlaps with the regions of resonant electromagnetic fields where biomolecular binding can produce the greatest shifts in photonic crystal resonant wavelength. Despite the nanoscale porosity of the sensor structure, the PC slab exhibits narrowband and high efficiency resonant reflection, enabling the structure to serve as a wavelength-tunable element of an external cavity laser. In the context of sensing small molecule interactions with much larger immobilized proteins, we demonstrate that the porous structure provides 3.7× larger biosensor signals than an equivalent nonporous structure, while the external cavity laser (ECL) detection method provides capability for sensing picometer-scale shifts in the PC resonant wavelength caused by small molecule binding. The porous ECL achieves a record high figure of merit for label-free optical biosensors.

2. Porous silicon gettering

SciTech Connect

Tsuo, Y.S.; Menna, P.; Al-Jassim, M.

1995-08-01

We have studied a novel extrinsic gettering method that utilizes the very large surface areas, produced by porous silicon etch on both front and back surfaces of the silicon wafer, as gettering sites. In this method, a simple and low-cost chemical etching is used to generate the porous silicon layers. Then, a high-flux solar furnace (HFSF) is used to provide high-temperature annealing and the required injection of silicon interstitials. The gettering sites, along with the gettered impurities, can be easily removed at the end the process. The porous silicon removal process consists of oxidizing the porous silicon near the end the gettering process followed by sample immersion in HF acid. Each porous silicon gettering process removes up to about 10 {mu}m of wafer thickness. This gettering process can be repeated so that the desired purity level is obtained.

3. Method for preparing dielectric composite materials

DOEpatents

Lauf, Robert J.; Anderson, Kimberly K.; Montgomery, Frederick C.; Collins, Jack L.; Felten, John J.

2004-11-23

The invention allows the fabrication of small, dense beads of dielectric materials with selected compositions, which are incorporated into a polymeric matrix for use in capacitors, filters, and the like. A porous, generally spherical bead of hydrous metal oxide containing titanium or zirconium is made by a sol-gel process to form a substantially rigid bead having a generally fine crystallite size and correspondingly finely distributed internal porosity. The resulting gel bead may be washed and hydrothermally reacted with a soluble alkaline earth salt (typically Ba or Sr) at elevated temperature and pressure to convert the bead into a mixed hydrous titanium- or zirconium-alkaline earth oxide while retaining the generally spherical shape. Alternatively, the gel bead may be made by coprecipitation. This mixed oxide bead is then washed, dried and calcined to produce the desired (BaTiO.sub.3, PbTiO.sub.3, SrZrO.sub.3) structure. The sintered beads are incorporated into a selected polymer matrix. The resulting dielectric composite material may be electrically "poled" if desired.

4. Dielectric composite materials and method for preparing

DOEpatents

Lauf, Robert J.; Anderson, Kimberly K.; Montgomery, Frederick C.; Collins, Jack L.; Felten, John J.

2003-07-29

The invention allows the fabrication of small, dense beads of dielectric materials with selected compositions, which are incorporated into a polymeric matrix for use in capacitors, filters, and the like. A porous, generally spherical bead of hydrous metal oxide containing titanium or zirconium is made by a sol-gel process to form a substantially rigid bead having a generally fine crystallite size and correspondingly finely distributed internal porosity. The resulting gel bead may be washed and hydrothermally reacted with a soluble alkaline earth salt (typically Ba or Sr) at elevated temperature and pressure to convert the bead into a mixed hydrous titanium- or zirconium-alkaline earth oxide while retaining the generally spherical shape. Alternatively, the gel bead may be made by coprecipitation. This mixed oxide bead is then washed, dried and calcined to produce the desired (BaTiO.sub.3, PbTiO.sub.3, SrZrO.sub.3) structure. The sintered beads are incorporated into a selected polymer matrix. The resulting dielectric composite material may be electrically "poled" if desired.

5. Experiments and Computational Theory for Electrical Breakdown in Critical Components: THz Imaging of Electronic Plasmas.

SciTech Connect

Zutavern, Fred J.; Hjalmarson, Harold P.; Bigman, Verle Howard; Gallegos, Richard Joseph

2016-11-01

This report describes the development of ultra-short pulse laser (USPL) induced terahertz (THz) radiation to image electronic plasmas during electrical breakdown. The technique uses three pulses from two USPLs to (1) trigger the breakdown, (2) create a 2 picosecond (ps, 10 -12 s), THz pulse to illuminate the breakdown, and (3) record the THz image of the breakdown. During this three year internal research program, sub-picosecond jitter timing for the lasers, THz generation, high bandwidth (BW) diagnostics, and THz image acquisition was demonstrated. High intensity THz radiation was optically-induced in a pulse-charged gallium arsenide photoconductive switch. The radiation was collected, transported, concentrated, and co-propagated through an electro-optic crystal with an 800 nm USPL pulse whose polarization was rotated due to the spatially varying electric field of the THz image. The polarization modulated USPL pulse was then passed through a polarizer and the resulting spatially varying intensity was detected in a high resolution digital camera. Single shot images had a signal to noise of %7E3:1. Signal to noise was improved to %7E30:1 with several experimental techniques and by averaging the THz images from %7E4000 laser pulses internally and externally with the camera and the acquisition system (40 pulses per readout). THz shadows of metallic films and objects were also recorded with this system to demonstrate free-carrier absorption of the THz radiation and improve image contrast and resolution. These 2 ps THz pulses were created and resolved with 100 femtosecond (fs, 10 -15 s) long USPL pulses. Thus this technology has the capability to time-resolve extremely fast repetitive or single shot phenomena, such as those that occur during the initiation of electrical breakdown. The goal of imaging electrical breakdown was not reached during this three year project. However, plans to achieve this goal as part of a follow-on project are described in this document

6. Model of dissipative dielectric elastomers

NASA Astrophysics Data System (ADS)

Chiang Foo, Choon; Cai, Shengqiang; Jin Adrian Koh, Soo; Bauer, Siegfried; Suo, Zhigang

2012-02-01

The dynamic performance of dielectric elastomer transducers and their capability of electromechanical energy conversion are affected by dissipative processes, such as viscoelasticity, dielectric relaxation, and current leakage. This paper describes a method to construct a model of dissipative dielectric elastomers on the basis of nonequilibrium thermodynamics. We characterize the state of the dielectric elastomer with kinematic variables through which external loads do work, and internal variables that measure the progress of the dissipative processes. The method is illustrated with examples motivated by existing experiments of polyacrylate very-high-bond dielectric elastomers. This model predicts the dynamic response of the dielectric elastomer and the leakage current behavior. We show that current leakage can be significant under large deformation and for long durations. Furthermore, current leakage can result in significant hysteresis for dielectric elastomers under cyclic voltage.

7. Hedgehog subwavelength hole arrays: control over the THz enhanced transmission

NASA Astrophysics Data System (ADS)

Navarro-Cía, M.; Rodriguez-Ulibarri, Pablo; Beruete, M.

2013-01-01

By backing or sandwiching a holey metal layer with or between isotropic dielectric slabs, additional peaks of transmission within the long-wavelength regime arise as a result of the induced transverse magnetic (TM) or transverse electric (TE) grounded dielectric modes. A similar control of the complex surface wave modes, and thus of the extraordinary transmission (ET) peaks, is demonstrated here via anisotropic slabs in the form of a fakir's bed of nails. However, it is shown that those ET peaks formed from TE modes are suppressed because of the inherent dispersion characteristics of the free-standing grounded pins. This allows the red-shifting of the ET for the polarization parallel to the larger in-plane period of the hole array, but unlike the dielectric isotropic slab configuration, the orthogonal polarization remains inhibited. In memoriam Professor Mario Sorolla.

8. Frequency Upshift and Radiation of the THz Electromagnetic Wave via an Ultrashort-Laser-Produced Ionization Front

SciTech Connect

Higashiguchi, Takeshi; Hasegawa, Hideyuki; Nishimai, Hirofumi; Yugami, Noboru; Muggli, Patric

2009-01-22

We report the generation of radiation in the terahertz (THz) spectral region from an electrostatic field converted by a laser-produced relativistic ionization front. The THz radiation is generated through spatiotemporal change in electron density induced by a relativistic ionization front propagating in a ZnSe crystal enclosed in a capacitor array. The measured central radiation frequency is 1.2 THz with a bandwidth of 0.7 THz (FWHM), which is attributed to production of an electron density of the order of 10{sup 15} cm{sup -3}. The amplitude of the linearly polarized THz radiation increased linearly with the voltage applied to the capacitors.

9. An all-dielectric route for terahertz cloaking

NASA Astrophysics Data System (ADS)

Gaillot, D. P.; Croënne, C.; Lippens, Didier

2008-04-01

An original all-dielectric design that performs cloaking at terahertz frequencies is demonstrated. The cloak consists of radially positioned discretized micrometer-sized cylindrical elements. Based on Mie theory and under adequate excitation conditions (H along the rod axis), high-κ cylinders exhibit a strong magnetic resonance dependent on the cylinder radii and material properties. Full-wave simulations coupled with a field-summation retrieval technique were employed to adjust the electromagnetic response of individual ferroelectrics rods (Ba 0.5Sr 0.5TiO 3; ɛ = 200 - tan δ = 2.10 -2). The rods magnetic plasma frequency was engineered such that the full cloak displays a progressive variation in its permeability radial component; hence satisfying, for this polarization, the reduced equations derived from the conformal transformation theory. The cloaking performance was assessed by modelling the complete micro-structured device. Results unambiguously show that cloaking of any wavelength scaled objects located inside the cloak is achieved above the Mie resonance frequency at 0.58 THz for the present device. In particular, the phase fronts of the electric field behind the device are well reconstructed with a high value in transmission of the incident plane wave. This also means that the absorption losses are small within the cloak in comparison with the metallic systems originally proposed. Although cloaking is observed in a narrow band, this all-dielectric configuration provides an attractive route for designing cloaking devices at microwave and terahertz frequencies.

10. Antenna with Dielectric Having Geometric Patterns

NASA Technical Reports Server (NTRS)

Dudley, Kenneth L. (Inventor); Elliott, Holly A. (Inventor); Cravey, Robin L. (Inventor); Connell, John W. (Inventor); Ghose, Sayata (Inventor); Watson, Kent A. (Inventor); Smith, Jr., Joseph G. (Inventor)

2013-01-01

An antenna includes a ground plane, a dielectric disposed on the ground plane, and an electrically-conductive radiator disposed on the dielectric. The dielectric includes at least one layer of a first dielectric material and a second dielectric material that collectively define a dielectric geometric pattern, which may comprise a fractal geometry. The radiator defines a radiator geometric pattern, and the dielectric geometric pattern is geometrically identical, or substantially geometrically identical, to the radiator geometric pattern.

11. Video rate imaging of narrow band THz radiation based on frequency upconversion

NASA Astrophysics Data System (ADS)

Tekavec, Patrick F.; Kozlov, Vladimir G.; Mcnee, Ian; Spektor, Igor E.; Lebedev, Sergey P.

2015-03-01

We demonstrate video rate THz imaging by detecting a frequency upconverted signal with a CMOS camera. A fiber laser pumped, double resonant optical parametric oscillator generates THz pulses via difference frequency generation in a quasi-phasematched gallium arsenide (QPM-GaAs) crystal located inside the OPO cavity. The output produced THz pulses centered at 1.5 THz, with an average power up to 1 mW, a linewidth of <100 GHz, and peak power of >2 W. By mixing the THz pulses with a portion of the fiber laser pump (1064 nm) in a second QPM-GaAs crystal, distinct sidebands are observed at 1058 nm and 1070 nm, corresponding to sum and difference frequency generation of the pump pule with the THz pulse. By using a polarizer and long pass filter, the strong pump light can be removed, leaving a nearly background free signal at 1070 nm. For imaging, a Fourier imaging geometry is used, with the object illuminated by the THz beam located one focal length from the GaAs crystal. The spatial Fourier transform is upconverted with a large diameter pump beam, after which a second lens inverse transforms the upconverted spatial components, and the image is detected with a CMOS camera. We have obtained video rate images with spatial resolution of 1mm and field of view ca. 20 mm in diameter without any post processing of the data.

12. THz pulse emission from InAs-based epitaxial structures grown on InP substrates

NASA Astrophysics Data System (ADS)

Nevinskas, I.; Butkutė, R.; Stanionytė, S.; Bičiūnas, A.; Geižutis, A.; Krotkus, A.

2016-11-01

Undoped InAs and InAs p-n junction epitaxial layers were grown on (100)-cut InP substrates with molecular beam epitaxy. The lattice difference between the substrate and the InAs layers was matched with a graded AlInAs buffer layer. The alloy composition, structural characteristics and carrier mobility of the structures were determined from the high-resolution x-ray diffraction, atomic force microscopy and Hall-effect measurements, respectively. The optical parameters of the layers were characterized by the emission of terahertz (THz) pulses when the samples were illuminated with femtosecond laser pulses. It has been found that the built-in electric field in the p-n junction enhances the THz emission. Registering THz signals in the quasi-reflection direction, the p-n junction emits more intense radiation in comparison to an undoped bulk InAs. At excitation wavelengths >1.8 μm the InAs p-n junction provides stronger THz pulses than those from (111)-cut p-InAs, the best surface THz emitter known to date. The epitaxial layers were also exposed to a constant magnetic field from neodymium permanent magnets, which further enhances THz emission and allows registering THz radiation in the line-of-sight terahertz time-domain-spectroscopy geometry.

13. Aligned copper nanorod arrays for highly efficient generation of intense ultra-broadband THz pulses

NASA Astrophysics Data System (ADS)

Mondal, S.; Wei, Q.; Ding, W. J.; Hafez, H. A.; Fareed, M. A.; Laramée, A.; Ropagnol, X.; Zhang, G.; Sun, S.; Sheng, Z. M.; Zhang, J.; Ozaki, T.

2017-01-01

We demonstrate an intense broadband terahertz (THz) source based on the interaction of relativistic-intensity femtosecond lasers with aligned copper nanorod array targets. For copper nanorod targets with a length of 5 μm, a maximum 13.8 times enhancement in the THz pulse energy (in ≤20 THz spectral range) is measured as compared to that with a thick plane copper target under the same laser conditions. A further increase in the nanorod length leads to a decrease in the THz pulse energy at medium frequencies (≤20 THz) and increase of the electromagnetic pulse energy in the high-frequency range (from 20–200 THz). For the latter, we measure a maximum energy enhancement of 28 times for the nanorod targets with a length of 60 μm. Particle-in-cell simulations reveal that THz pulses are mostly generated by coherent transition radiation of laser produced hot electrons, which are efficiently enhanced with the use of nanorod targets. Good agreement is found between the simulation and experimental results.

14. THz photonic wireless links with 16-QAM modulation in the 375-450 GHz band.

PubMed

Jia, Shi; Yu, Xianbin; Hu, Hao; Yu, Jinlong; Guan, Pengyu; Da Ros, Francesco; Galili, Michael; Morioka, Toshio; Oxenløwe, Leif K

2016-10-17

We propose and experimentally demonstrate THz photonic wireless communication systems with 16-QAM modulation in the 375-450 GHz band. The overall throughput reaches as high as 80 Gbit/s by exploiting four THz channels with 5 Gbaud 16-QAM baseband modulation per channel. We create a coherent optical frequency comb (OFC) for photonic generation of multiple THz carriers based on photo-mixing in a uni-travelling carrier photodiode (UTC-PD). The OFC configuration also allows us to generate reconfigurable THz carriers with low phase noise. The multiple-channel THz radiation is received by using a Schottky mixer based electrical receiver after 0.5 m free-space wireless propagation. 2-channel (40 Gbit/s) and 4-channel (80 Gbit/s) THz photonic wireless links with 16-QAM modulation are reported in this paper, and the bit error rate (BER) performance for all channels in both cases is below the hard decision forward error correction (HD-FEC) threshold of 3.8e-3 with 7% overhead. In addition, we also successfully demonstrate hybrid photonic wireless transmission of 40 Gbit/s 16-QAM signal at carrier frequencies of 400 GHz and 425 GHz over 30 km standard single mode fiber (SSMF) between the optical baseband signal transmitter and the THz wireless transmitter with negligible induced power penalty.

15. Aligned copper nanorod arrays for highly efficient generation of intense ultra-broadband THz pulses

PubMed Central

Mondal, S.; Wei, Q.; Ding, W. J.; Hafez, H. A.; Fareed, M. A.; Laramée, A.; Ropagnol, X.; Zhang, G.; Sun, S.; Sheng, Z. M.; Zhang, J.; Ozaki, T.

2017-01-01

We demonstrate an intense broadband terahertz (THz) source based on the interaction of relativistic-intensity femtosecond lasers with aligned copper nanorod array targets. For copper nanorod targets with a length of 5 μm, a maximum 13.8 times enhancement in the THz pulse energy (in ≤20 THz spectral range) is measured as compared to that with a thick plane copper target under the same laser conditions. A further increase in the nanorod length leads to a decrease in the THz pulse energy at medium frequencies (≤20 THz) and increase of the electromagnetic pulse energy in the high-frequency range (from 20–200 THz). For the latter, we measure a maximum energy enhancement of 28 times for the nanorod targets with a length of 60 μm. Particle-in-cell simulations reveal that THz pulses are mostly generated by coherent transition radiation of laser produced hot electrons, which are efficiently enhanced with the use of nanorod targets. Good agreement is found between the simulation and experimental results. PMID:28071764

16. The study of gas species on THz generation from laser-induced air plasma

NASA Astrophysics Data System (ADS)

Zhao, Ji; Zhang, LiangLiang; Wu, YiJian; Wu, Tong; Yuan, Hui; Zhang, CunLin; Zhao, YueJin

2015-08-01

Intense Terahertz waves generated from air-induced plasma and serving as broadband THz source provide a promising broadband source for innovative technology. Terahertz generation in selected gases has attracted more and more researchers' interests in recent years. In this research, the THz emission from different atoms is described, such as nitrogen, argon and helium in Michelson. The THz radiation is detected by a Golay Cell equipped with a 6-mm-diameter diamond-inputting window. It can be seen in the first time that when the pump power lies at a stable level, the THz generation created by the femtosecond laser focusing on the nitrogen is higher than which focusing on the helium, and lower than that produced in the argon gas environment. We believe that the THz intensity is Ar > N > Ne because of its atomic mass, which is Ar > N > Ne as well. It is clear that the Gas molecular decides the release of free electrons ionized from ultra short femtosecond laser through the electronic dynamic analysis. The higher the gas mass is, the stronger the terahertz emission will be. We further explore the THz emission at the different laser power levels, and the experimental results can be commendably quadratic fitted. It can be inferred that THz emission under different gas medium environment still complies with the law of four-wave mixing (FWM) process and has nothing to do with the gas environment: the radiation energy is proportional to the quadratic of incident laser power.

17. Aligned copper nanorod arrays for highly efficient generation of intense ultra-broadband THz pulses.

PubMed

Mondal, S; Wei, Q; Ding, W J; Hafez, H A; Fareed, M A; Laramée, A; Ropagnol, X; Zhang, G; Sun, S; Sheng, Z M; Zhang, J; Ozaki, T

2017-01-10

We demonstrate an intense broadband terahertz (THz) source based on the interaction of relativistic-intensity femtosecond lasers with aligned copper nanorod array targets. For copper nanorod targets with a length of 5 μm, a maximum 13.8 times enhancement in the THz pulse energy (in ≤20 THz spectral range) is measured as compared to that with a thick plane copper target under the same laser conditions. A further increase in the nanorod length leads to a decrease in the THz pulse energy at medium frequencies (≤20 THz) and increase of the electromagnetic pulse energy in the high-frequency range (from 20-200 THz). For the latter, we measure a maximum energy enhancement of 28 times for the nanorod targets with a length of 60 μm. Particle-in-cell simulations reveal that THz pulses are mostly generated by coherent transition radiation of laser produced hot electrons, which are efficiently enhanced with the use of nanorod targets. Good agreement is found between the simulation and experimental results.

18. Intense picosecond THz pulses alter gene expression in human skin tissue in vivo

NASA Astrophysics Data System (ADS)

Titova, Lyubov V.; Ayesheshim, Ayesheshim K.; Golubov, Andrey; Rodriguez-Juarez, Rocio; Kovalchuk, Anna; Hegmann, Frank A.; Kovalchuk, Olga

2013-02-01

Pulsed terahertz (THz) imaging has been suggested as a novel high resolution, noninvasive medical diagnostic tool. However, little is known about the influence of pulsed THz radiation on human tissue, i.e., its genotoxicity and effects on cell activity and cell integrity. We have carried out a comprehensive investigation of the biological effects of THz radiation on human skin tissue using a high power THz pulse source and an in vivo full-thickness human skin tissue model. We have observed that exposure to intense THz pulses causes DNA damage and changes in the global gene expression profile in the exposed skin tissue. Several of the affected genes are known to play major roles in human cancer. While the changes in the expression levels of some of them suggest possible oncogenic effects of pulsed THz radiation, changes in the expression of the other cancer-related genes might have a protective influence. This study may serve as a roadmap for future investigations aimed at elucidating the exact roles that all the affected genes play in skin carcinogenesis and in response to pulsed THz radiation.

19. Broadband Terahertz Computed Tomography Using a 5k-pixel Real-time THz Camera

NASA Astrophysics Data System (ADS)

Trichopoulos, Georgios C.; Sertel, Kubilay

2015-07-01

We present a novel THz computed tomography system that enables fast 3-dimensional imaging and spectroscopy in the 0.6-1.2 THz band. The system is based on a new real-time broadband THz camera that enables rapid acquisition of multiple cross-sectional images required in computed tomography. Tomographic reconstruction is achieved using digital images from the densely-packed large-format (80×64) focal plane array sensor located behind a hyper-hemispherical silicon lens. Each pixel of the sensor array consists of an 85 μm × 92 μm lithographically fabricated wideband dual-slot antenna, monolithically integrated with an ultra-fast diode tuned to operate in the 0.6-1.2 THz regime. Concurrently, optimum impedance matching was implemented for maximum pixel sensitivity, enabling 5 frames-per-second image acquisition speed. As such, the THz computed tomography system generates diffraction-limited resolution cross-section images as well as the three-dimensional models of various opaque and partially transparent objects. As an example, an over-the-counter vitamin supplement pill is imaged and its material composition is reconstructed. The new THz camera enables, for the first time, a practical application of THz computed tomography for non-destructive evaluation and biomedical imaging.

20. Preparation of asymmetric porous materials

DOEpatents

Coker, Eric N [Albuquerque, NM

2012-08-07

A method for preparing an asymmetric porous material by depositing a porous material film on a flexible substrate, and applying an anisotropic stress to the porous media on the flexible substrate, where the anisotropic stress results from a stress such as an applied mechanical force, a thermal gradient, and an applied voltage, to form an asymmetric porous material.

1. Hydration shell parameters of aqueous alcohols: THz excess absorption and packing density.

PubMed

Matvejev, V; Zizi, M; Stiens, J

2012-12-06

Solvation in water requires minimizing the perturbations in its hydrogen bonded network. Hence solutes distort water molecular motions in a surrounding domain, forming a molecule-specific hydration shell. The properties of those hydration shells impact the structure and function of the solubilized molecules, both at the single molecule and at higher order levels. The size of the hydration shell and the picoseconds time-scale water dynamics retardation are revealed by terahertz (THz) absorption coefficient measurements. Room-temperature absorption coefficient at f = 0.28 [THz] is measured as a function of alcohol concentration in aqueous methanol, ethanol, 1,2-propanol, and 1-butanol solutions. Highly diluted alcohol measurements and enhanced overall measurement accuracy are achieved with a THz absorption measurement technique of nL-volume liquids in a capillary tube. In the absorption analysis, bulk and interfacial molecular domains of water and alcohol are considered. THz ideal and excess absorption coefficients are defined in accordance with thermodynamics mixing formulations. The parameter extraction method is developed based on a THz excess absorption model and hydrated solute molecule packing density representation. First, the hydration shell size is deduced from the hydrated solute packing densities at two specific THz excess absorption nonlinearity points: at infinite alcohol dilution (IAD) and at the THz excess absorption extremum (EAE). Consequently, interfacial water and alcohol molecular domain absorptions are deduced from the THz excess absorption model. The hydration shell sizes obtained at the THz excess absorption extremum are in excellent agreement with other reports. The hydration shells of methanol, ethanol, 1- and 2-propanol consist of 13.97, 22.94, 22.99, and 31.10 water molecules, respectively. The hydration shell water absorption is on average 0.774 ± 0.028 times the bulk water absorption. The hydration shell parameters might shed light on

2. Solar Observations at THz Frequencies on Board of a Trans-Antartic Stratospheric Balloon Flight

NASA Astrophysics Data System (ADS)

Kaufmann, Pierre; Abrantes, André; Bortolucci, Emilio; Caspi, Amir; Fernandes, Luis Olavo T.; Kropotov, Grigory; Kudaka, Amauri; Laurent, Glenn Thomas; Machado, Nelson; Marcon, Rogério; Marun, Adolfo; Nicolaev, Valery; Hidalgo Ramirez, Ray Fernando; Raulin, Jean-Pierre; Saint-Hilaire, Pascal; Shih, Albert; Silva, Claudemir; Timofeevsky, Alexander

2016-05-01

Sub-THz and 30 THz solar burst observations revealed a new spectral component, with fluxes increasing towards THz frequencies, simultaneously with the well known component peaking at microwaves, bringing challenging constraints for interpretation. The THz flare spectra can be completed with measurements made from space. A new system of two photometers was built to observe the Sun at 3 and 7 THz named SOLAR-T. An innovative optical setup allows observations of the full solar disk and detect small burst with sub-second time resolution. The photometers use two Golay cell detectors at the foci of 7.6 cm Cassegrain telescopes. The incoming radiation undergoes low-pass filters made of rough surface primary mirrors and membranes, 3 and 7 THz band-pass filters, and choppers. The system has been integrated to redundant data acquisition system and Iridium short-burst data services telemetry for monitoring during the flight. SOLAR-T has been flown coupled to U.C. Berkeley solar hard X-ray and gamma-ray imaging spectro-polarimeter GRIPS experiment launched on a NASA CSBF stratospheric balloon from U.S. McMurdo base on January 19, 2016, on a trans-Antarctic flight. The mission ended on January 30. The SOLAR-T on-board computers were recovered from the payload that landed in the Argentina Mountain Range, nearly 2100 km from McMurdo. The SOLAR-T performance was successfully attained, with full space qualification instrumentation. Preliminary results provide the solar disk THz brightness temperatures and indicate a 7 THz burst enhancement time coincident to a sub-THz burst observed by SST during the 28 January GOES C9.6 class soft X-ray burst, the largest occurred during the flight.

3. Fabricating porous silicon carbide

NASA Technical Reports Server (NTRS)

Shor, Joseph S. (Inventor); Kurtz, Anthony D. (Inventor)

1994-01-01

The formation of porous SiC occurs under electrochemical anodization. A sample of SiC is contacted electrically with nickel and placed into an electrochemical cell which cell includes a counter electrode and a reference electrode. The sample is encapsulated so that only a bare semiconductor surface is exposed. The electrochemical cell is filled with an HF electrolyte which dissolves the SiC electrochemically. A potential is applied to the semiconductor and UV light illuminates the surface of the semiconductor. By controlling the light intensity, the potential and the doping level, a porous layer is formed in the semiconductor and thus one produces porous SiC.

4. Temperature switchable polymer dielectrics.

SciTech Connect

Kholwadwala, Fenil Manish; Johnson, Ross Stefan; Dirk, Shawn M.

2010-06-01

Materials with switchable states are desirable in many areas of science and technology. The ability to thermally transform a dielectric material to a conductive state should allow for the creation of electronics with built-in safety features. Specifically, the non-desirable build-up and discharge of electricity in the event of a fire or over-heating would be averted by utilizing thermo-switchable dielectrics in the capacitors of electrical devices (preventing the capacitors from charging at elevated temperatures). We have designed a series of polymers that effectively switch from a non-conductive to a conductive state. The thermal transition is governed by the stability of the leaving group after it leaves as a free entity. Here, we present the synthesis and characterization of a series of precursor polymers that eliminate to form poly(p-phenylene vinylene) (PPV's).

5. Broadband local dielectric spectroscopy

NASA Astrophysics Data System (ADS)

Labardi, M.; Lucchesi, M.; Prevosto, D.; Capaccioli, S.

2016-05-01

A route to extend the measurement bandwidth of local dielectric spectroscopy up to the MHz range has been devised. The method is based on a slow amplitude modulation at a frequency Ω of the excitation field oscillating at a frequency ω and the coherent detection of the modulated average electric force or force gradient at Ω. The cantilever mechanical response does not affect the measurement if Ω is well below its resonant frequency; therefore, limitations on the excitation field frequency are strongly reduced. Demonstration on a thin poly(vinyl acetate) film is provided, showing its structural relaxation spectrum on the local scale up to 45 °C higher than glass temperature, and nanoscale resolution dielectric relaxation imaging near conductive nanowires embedded in the polymer matrix was obtained up to 5 MHz frequency, with no physical reason to hinder further bandwidth extension.

6. Temperature switchable polymer dielectrics.

SciTech Connect

Johnson, Ross Stefan

2010-08-01

Materials with switchable states are desirable in many areas of science and technology. The ability to thermally transform a dielectric material to a conductive state should allow for the creation of electronics with built-in safety features. Specifically, the non-desirable build-up and discharge of electricity in the event of a fire or over-heating would be averted by utilizing thermo-switchable dielectrics in the capacitors of electrical devices (preventing the capacitors from charging at elevated temperatures). We have designed a series of polymers that effectively switch from a non-conductive to a conductive state. The thermal transition is governed by the stability of the leaving group after it leaves as a free entity. Here, we present the synthesis and characterization of a series of precursor polymers that eliminate to form poly(p-phenylene vinylene) (PPV's).

7. DIELECTRIC WALL ACCELERATOR TECHNOLOGY

SciTech Connect

Sampayan, S; Caporaso, G; Chen, Y; Harris, J; Hawkins, S; Holmes, C; Nelson, S; Poole, B; Rhodes, M; Sanders, D; Sullivan, J; Wang, L; Watson, J

2007-10-18

The dielectric wall accelerator (DWA) is a compact pulsed power device where the pulse forming lines, switching, and vacuum wall are integrated into a single compact geometry. For this effort, we initiated a extensive compact pulsed power development program and have pursued the study of switching (gas, oil, laser induced surface flashover and photoconductive), dielectrics (ceramics and nanoparticle composites), pulse forming line topologies (asymmetric and symmetric Blumleins and zero integral pulse forming lines), and multilayered vacuum insulator (HGI) technology. Finally, we fabricated an accelerator cell for test on ETAII (a 5.5 MeV, 2 kA, 70 ns pulsewidth electron beam accelerator). We review our past results and report on the progress of accelerator cell testing.

8. All-dielectric metamaterials

NASA Astrophysics Data System (ADS)

Jahani, Saman; Jacob, Zubin

2016-01-01

The ideal material for nanophotonic applications will have a large refractive index at optical frequencies, respond to both the electric and magnetic fields of light, support large optical chirality and anisotropy, confine and guide light at the nanoscale, and be able to modify the phase and amplitude of incoming radiation in a fraction of a wavelength. Artificial electromagnetic media, or metamaterials, based on metallic or polar dielectric nanostructures can provide many of these properties by coupling light to free electrons (plasmons) or phonons (phonon polaritons), respectively, but at the inevitable cost of significant energy dissipation and reduced device efficiency. Recently, however, there has been a shift in the approach to nanophotonics. Low-loss electromagnetic responses covering all four quadrants of possible permittivities and permeabilities have been achieved using completely transparent and high-refractive-index dielectric building blocks. Moreover, an emerging class of all-dielectric metamaterials consisting of anisotropic crystals has been shown to support large refractive index contrast between orthogonal polarizations of light. These advances have revived the exciting prospect of integrating exotic electromagnetic effects in practical photonic devices, to achieve, for example, ultrathin and efficient optical elements, and realize the long-standing goal of subdiffraction confinement and guiding of light without metals. In this Review, we present a broad outline of the whole range of electromagnetic effects observed using all-dielectric metamaterials: high-refractive-index nanoresonators, metasurfaces, zero-index metamaterials and anisotropic metamaterials. Finally, we discuss current challenges and future goals for the field at the intersection with quantum, thermal and silicon photonics, as well as biomimetic metasurfaces.

9. Dielectric spectroscopy of polyaniline

SciTech Connect

Calleja, R.D.; Matveeva, E.M.

1993-12-31

Polyaniline films (PANI) are being considered as attractive new galvanic sources, electrochromic displays, chemical sensors, etc. So far much work has been done to study their optical, electrochemical and electrical properties. However, there are still doubts about the basic electric conductivity mechanisms of PANI. The aim of this paper is to study the influence of water molecules and acid anions on the properties of PANI films by dielectric spectroscopy.

10. All-dielectric metamaterials.

PubMed

Jahani, Saman; Jacob, Zubin

2016-01-01

The ideal material for nanophotonic applications will have a large refractive index at optical frequencies, respond to both the electric and magnetic fields of light, support large optical chirality and anisotropy, confine and guide light at the nanoscale, and be able to modify the phase and amplitude of incoming radiation in a fraction of a wavelength. Artificial electromagnetic media, or metamaterials, based on metallic or polar dielectric nanostructures can provide many of these properties by coupling light to free electrons (plasmons) or phonons (phonon polaritons), respectively, but at the inevitable cost of significant energy dissipation and reduced device efficiency. Recently, however, there has been a shift in the approach to nanophotonics. Low-loss electromagnetic responses covering all four quadrants of possible permittivities and permeabilities have been achieved using completely transparent and high-refractive-index dielectric building blocks. Moreover, an emerging class of all-dielectric metamaterials consisting of anisotropic crystals has been shown to support large refractive index contrast between orthogonal polarizations of light. These advances have revived the exciting prospect of integrating exotic electromagnetic effects in practical photonic devices, to achieve, for example, ultrathin and efficient optical elements, and realize the long-standing goal of subdiffraction confinement and guiding of light without metals. In this Review, we present a broad outline of the whole range of electromagnetic effects observed using all-dielectric metamaterials: high-refractive-index nanoresonators, metasurfaces, zero-index metamaterials and anisotropic metamaterials. Finally, we discuss current challenges and future goals for the field at the intersection with quantum, thermal and silicon photonics, as well as biomimetic metasurfaces.

11. Evolution of the high power THz source program at Jefferson Lab

SciTech Connect

George Neil; Gwyn Williams

2004-10-01

We report the evolution of the high power THz source program at Jefferson Lab. The source is based on coherent synchrotron radiation in which short bunches of relativistic electrons radiate when traversing a dipolar magnetic field. In our first accelerator we produced 20 W of broadband THz light. Our upgraded accelerator with higher current and improved THz extraction optics will considerably enhance the output power to >100 W. In this paper we describe the source in some detail and present theoretical calculations for the upgrade.

12. Fra Angelico's painting technique revealed by terahertz time-domain imaging (THz-TDI)

NASA Astrophysics Data System (ADS)

Koch Dandolo, Corinna Ludovica; Picollo, Marcello; Cucci, Costanza; Jepsen, Peter Uhd

2016-10-01

We have investigated with terahertz time-domain imaging (THz-TDI) the well-known Lamentation over the dead Christ panel painting (San Marco Museum, Florence) painted by Fra Giovanni Angelico within 1436 and 1441. The investigation provided a better understanding of the construction and gilding technique used by the eminent artist, as well as the plastering technique used during the nineteenth-century restoration intervention. The evidence obtained from THz-TDI scans was correlated with the available documentation on the preservation history of the art piece. Erosion and damages documented for the wooden support, especially in the lower margin, found confirmation in the THz-TD images.

13. Tunable narrowband THz pulse generation in scalable large area photoconductive antennas.

PubMed

Krause, Johannes; Wagner, Martin; Winnerl, Stephan; Helm, Manfred; Stehr, Dominik

2011-09-26

The generation and characterization of narrowband THz pulses by means of chirped pulse difference frequency generation in Auston-switch type photoconductive antennas is reported. Using optical pulses with energies in the range from 1 nJ to 1 µJ, we generate THz pulses with up to 50 pJ in energy and electric field strengths on the order of 1 kV/cm. Two emitter concepts are investigated and circumvention of the fast saturation for small area excitation by scaling of the THz emitter is demonstrated.

14. Steerable THz pulses from thin emitters via optical pulse-front tilt.

PubMed

Smith, B C; Whitaker, J F; Rand, S C

2016-09-05

A new method of steering THz pulses radiated from a thin emitter excited by tilted optical pulse-fronts has been developed theoretically and validated in a proof-of-concept experiment. This steering technique is potentially efficient and rapid, and it should benefit from a THz-pulse energy that can scale with optical-beam size and magnitude. Conversely, the method employed for measuring the steered THz pulses is also capable of characterizing the pulse-front tilt of an optical beam.

15. Carbon nanotube quantum dots as highly sensitive THz spectrometers

NASA Astrophysics Data System (ADS)

Rinzan, Mohamed; Jenkins, Greg; Drew, Dennis; Shafranjuk, Serhii; Barbara, Paola

2012-02-01

We show that carbon nanotube quantum dots (CNT-Dots) coupled to antennas are extremely sensitive, broad-band, terahertz quantum detectors. Their response is due to photon-assisted single-electron tunneling (PASET)[1], but cannot be fully understood with orthodox PASET models[2]. We consider intra-dot excitations and non-equilibrium cooling to explain the anomalous response. REFERENCES: [1] Y. Kawano, S. Toyokawa, T. Uchida and K. Ishibashi, THz photon assisted tunneling in carbon-nanotube quantum dots, Journal of Applied Physics 103, 034307 (2008). [2] P. K. Tien and J. P. Gordon, Multiphoton Process Observed in the Interaction of Microwave Fields with the Tunneling between Superconductor Films, Phys. Rev. 129, 647 (1963).

16. THz impulse radar for biomedical sensing: nonlinear system behavior

NASA Astrophysics Data System (ADS)

Brown, E. R.; Sung, Shijun; Grundfest, W. S.; Taylor, Z. D.

2014-03-01

The THz impulse radar is an "RF-inspired" sensor system that has performed remarkably well since its initial development nearly six years ago. It was developed for ex vivo skin-burn imaging, and has since shown great promise in the sensitive detection of hydration levels in soft tissues of several types, such as in vivo corneal and burn samples. An intriguing aspect of the impulse radar is its hybrid architecture which combines the high-peak-power of photoconductive switches with the high-responsivity and -bandwidth (RF and video) of Schottky-diode rectifiers. The result is a very sensitive sensor system in which the post-detection signal-to-noise ratio depends super-linearly on average signal power up to a point where the diode is "turned on" in the forward direction, and then behaves quasi-linearly beyond that point. This paper reports the first nonlinear systems analysis done on the impulse radar using MATLAB.

17. The role of THz and submillimeter wave technology in DHS

NASA Astrophysics Data System (ADS)

Coty, Thomas; Fuller-Tedeschi, Anna

2011-06-01

THz and submillimeter wave technology is of great interest to DHS S&T due to the non-ionizing and clothing penetrating properties of the spectral region. Imaging in the region allows for standoff imaging of concealed threats such as Improvised Explosive Devices (IED) at operationally relevant distances. DHS S&T is investing in this area with the development of components such as detectors and sources for active imaging as well as full sensor systems in the future. The fundamental characterization of the region is also being explored with DHS funding by imaging well-characterized rough surface scattering targets. Analysis of these images will yield data to be used in evaluating assumptions currently made in current performance models. This along with the relevant field applications will be addressed.

18. A THz heterodyne instrument for biomedical imaging applications

NASA Technical Reports Server (NTRS)

Siegel, Peter H.

2004-01-01

An ultra-wide-dynamic-range heterodyne imaging system operating at 2.5 THz is described. The instrument employs room temperature Schottky barrier diode mixers and far infrared gas laser sources developed for NASA space applications. A dynamic range of over 100dB at fixed intermediate frequencies has been realized. Amplitude/phase tracking circuitry results in stability of 0.02 dB and +-2 degrees of phase. The system is being employed to characterize biological (human and animal derived tissues) and a variety of materials of interest to NASA. This talk will describe the instrument and some of the early imaging experiments on everything from mouse tail to aerogel.

19. The new design of the THz streak camera at PSI

NASA Astrophysics Data System (ADS)

Gorgisyan, I.; Juranic, P. N.; Ischebeck, R.; Stepanov, A.; Schlott, V.; Pradervand, C.; Patthey, L.; Radovic, M.; Abela, R.; Hauri, C. P.; Monoszlai, B.; Ivanov, R.; Peier, P.; Liu, J.; Togashi, T.; Owada, S.; Ogawa, K.; Katayama, T.; Yabashi, M.; Rivkin, L.

2015-05-01

SwissFEL is the Free Electron Laser (FEL) facility under construction at the Paul Scherrer institute (PSI), aiming to provide users with X-ray pulses of lengths down to 2 femtoseconds at standard operation. The measurement of the length of the FEL pulses and their arrival time relative to the experimental laser is crucial for the pump-probe experiments carried out in such facilities. This work presents a new device that measures hard X-ray FEL pulses based on the THz streak camera concept. It describes the prototype setup called pulse arrival and length monitor (PALM) developed at PSI and tested in Spring-8 Angstrom Compact Free Electron Laser (SACLA) in Japan. Based on the first results obtained from the measurements, we introduce the new improved design of the second generation PALM setup that is currently under construction and will be used in SwissFEL photon diagnostics.

20. Space-Charge Modulation in Vacuum Microdiodes at THz Frequencies

SciTech Connect

Pedersen, Andreas; Manolescu, Andrei; Valfells, Agust

2010-04-30

We investigate the dynamics of a space-charge limited, photoinjected, electron beam in a microscopic vacuum diode. Because of the small nature of the system it is possible to conduct high-resolution simulations where the number of simulated particles is equal to the number of electrons within the system. In a series of simulations of molecular dynamics type, where electrons are treated as point charges, we address and analyze space-charge effects in a micrometer-scale vacuum diode. We have been able to reproduce breakup of a single pulse injected with a current density beyond the Child-Langmuir limit, and we find that continuous injection of current into the diode gap results in a well-defined train of electron bunches corresponding to THz frequency. A simple analytical explanation of this behavior is given.

1. Mode analysis and design of 0.3-THz Clinotron

NASA Astrophysics Data System (ADS)

Li, Shuang; Wang, Jian-Guo; Wang, Guang-Qiang; Zeng, Peng; Wang, Dong-Yang

2016-10-01

To develop a high-power continuous-wave terahertz source, a Clinotron operating at 0.3 THz is investigated. Based on the analyses of field distribution and coupling impedance, the dispersion characteristic of a rectangular resonator is preliminarily studied. The effective way to select fundamental mode to interact with the electron beam is especially studied. Finally, the structure is optimized by particle-in-cell simulation, and the problems of manufacture tolerance, current density threshold, and heat dissipation during Clinotron’s operation are also discussed. The optimum device can work with a good performance under the conditions of 8 kV and 60 mA. With the generation of signal frequency at 315.89 GHz and output power at 12 W on average, this device shows great prospects in the application of terahertz waves. Project supported by the National Natural Science Foundation of China (Grant No. 61231003).

2. Determination of stereoisomer in sugars by THz-TDS

NASA Astrophysics Data System (ADS)

Yamauchi, S.; Imai, Y.; Yokota, H.; Tonouchi, M.

2011-08-01

Transmission-type terahertz time-domain spectroscopy (THz-TDS) using dipole-antennas on LT-GaAs layers as THzemitter and detector with fs-fiber laser as the excitation light source was applied to determine the stereoisomer of sugars in carefully controlled environment with low humidity below 5% at 20°C. Commercially available α-D-lactose including about 4% anomer and β-D-lactose including below 30% anomer were used as stereoisomer samples. The absorption spectra of compounds by the α-D- and β-D-lactose powders with various ratios were successively deconvoluted to four spectra by Lorentzian and dependent on the composition ratio. Integrated absorptions due to α-D-lactose and β-D-lactose determined the decreasing rate (rα) and the increasing rate (rβ) for the composition ratio of the β-D-lactose powder, because the intensities were linearly dependent on the composition ratio. The net-composition ratio of α-lactose and β-lactose in the compounds was precisely evaluated by the ratio of the integrated intensities and the value of rβ / rα, for example, the anomer-contents in commercially available α-D-lactose and β-D-lactose powders were disclosed as 3.9% and 29.1%, respectively. The demonstrated results indicate that THz-TDS is so useful not only for precise qualitativeanalysis but also for precise quantitative-analysis of stereoisomer in sugars with partially different molecular structure such as lactose.

3. Continuous Monitoring of Photolysis Products by Thz Spectroscopy

NASA Astrophysics Data System (ADS)

Omar, Abdelaziz; Cuisset, Arnaud; Mouret, Gaël; Hindle, Francis; Eliet, Sophie; Bocquet, Robin

2015-06-01

We demonstrate the potential of THz spectroscopy to monitor the real time evolution of the gas phase concentration of photolysis products and determine the kinetic reaction rate constant. In the primary work, we have chosen to examine the photolysis of formaldehyde (H_2CO). Exposure of H_2CO to a UVB light (250 to 360 nm) in a single pass of 135 cm length cell leads to decomposition via two mechanisms: the radical channel with production of HCO and the molecular channel with production of CO. A commercial THz source (frequency multiplication chain) operating in the range 600-900 GHz was used to detect and quantify the various chemical species as a function of time. Monitoring the concentrations of CO and H_2CO via rotational transitions, allowed the kinetic rate of H_2CO consummation to be obtained, and an estimation of the rate constants for both the molecular and radical photolysis mechanisms. We have modified our experimental setup to increase the sensitivity of the spectrometer and changed sample preparation protocol specifically to quantify the HCO concentration. Acetaldehyde was used as the precursor for photolysis by UVC resulting in the decompositon mechanism can be described by: CH_3CHO+hν→ CH_3 + HCO → CH_4 + CO Frequency modulation of the source and Zeeman modulation is used to achieve the high sensitivity required. Particular attention has been paid to the mercury photosensitization effect that allowed us to increase the HCO production enabling quantification of the monitored radical. We quantify the HCO radical and start a spectroscopic study of the line positions. H. M. Pickett and T. L. Boyd, Chem. Phys. Lett, Vol 58, 446-449, (1978) S. Eliet, A. Cuisset, M Guinet, F. Hindle, G. Mouret, R. Bocquet, and J. Demaison, Journal of Molecular Spectroscopy, Vol 279, 12-15 (2012). G. Mouret, M. Guinet, A. Cuisset, L. Croizé, S. Eliet, R. Bocquet and F. Hindle, Sensors Journal. IEEE, Vol 13, 133 - 138, (2013)

4. Robust identification of concealed dangerous substances using THz imaging spectroscopy

NASA Astrophysics Data System (ADS)

Nystad, Helle E.; Haakestad, Magnus W.; van Rheenen, Arthur D.

2015-05-01

False alarm rates must be kept sufficiently low if a method to detect and identify objects or substances is to be implemented in real life applications. This is also true when trying to detect and identify dangerous substances such as explosives and drugs that are concealed in packaging materials. THz technology may be suited to detect these substances, especially when imaging and spectroscopy are combined. To achieve reasonable throughput, the detection and identification process must be automated and this implies reliance on algorithms to perform this task, rather than human beings. The identification part of the algorithm must compare spectral features of the unknown substance with those in a library of features and determining the distance, in some sense, between these features. If the distance is less than some defined threshold a match is declared. In this paper we consider two types of spectral characteristic that are derived from measured time-domain signals measured in the THz regime: the absorbance and its derivative. Also, we consider two schemes to measure the distance between the unknown and library characteristics: Spectral Angle Mapping (SAM) and Principal Component Analysis (PCA). Finally, the effect of windowing of the measured time-domain signal on the performance of the algorithms is studied, by varying the Blackman-Harris (B-H) window width. Algorithm performance is quantified by studying the receiver-operating characteristics (ROC). For the data considered in this study we conclude that the best performance is obtained when the derivative of the absorbance is used in combination with a narrow B-H window and SAM. SAM is a more straight-forward method and requires no large training data sets and tweaking.

5. Interaction of a relativistic electron beam with radiation in the THz frequency range

NASA Astrophysics Data System (ADS)

Sung, Chieh

The ability to generate a train of microbunches that are only typically tens of femtosecond wide and are separated by a picosecond is a topic of contemporary interest in the field of free electron lasers and plasma based accelerators. Moreover the usefulness of the high gradients present in plasma accelerators will depend on the ability to obtain mono-energetic relativistic electrons. This means that in addition to being prebunched on a scale shorter than the plasma wavelength the externally injected electron beam must be phase-locked to the accelerating plasma wave structure. In this thesis we investigate two techniques, Free Electron Laser interaction (FEL) and the Inverse Free Electron Laser interaction (IFEL), by which a medium energy electron beam can be prebunched into a series of microbunches with the same periodicity as a plasma wave and is phase locked to it. Using full-scale, 3-D simulations we show in this thesis that when a relativistic electron beam and an electromagnetic wave propagate collinearly through a magnetic undulator, FEL and IFEL interactions have the capability to form electron microbunches with periodicity 300-100 mum (1-3 THz range), which contain 50% of electrons within a small fraction of the ponderomotive buckets. Such a bunched beam is suitable for injection into plasma densities in the range 1016-1017 cm-3, respectively. Microbunching using the FEL mechanism requires a narrowband THz radiation source to act as a seed whereas the IFEL mechanism requires, in addition, such a source to be high power. In this thesis the generation of THz radiation in the Neptune Laboratory by mixing of two CO2 laser lines in a non-collinearly phase matched GaAs at room temperature is described A high-power THz pulse with up to 2 MW of peak power in a 250 ps pulse was generated using a TW class CO2 laser pulse. Such high power THz radiation is needed for the IFEL approach to microbunching. We also produced a high repetition rate THz source tunable in the

6. Tunable dielectric properties of ferrite-dielectric based metamaterial.

PubMed

Bi, K; Huang, K; Zeng, L Y; Zhou, M H; Wang, Q M; Wang, Y G; Lei, M

2015-01-01

A ferrite-dielectric metamaterial composed of dielectric and ferrite cuboids has been investigated by experiments and simulations. By interacting with the electromagnetic wave, the Mie resonance can take place in the dielectric cuboids and the ferromagnetic precession will appear in the ferrite cuboids. The magnetic field distributions show the electric Mie resonance of the dielectric cuboids can be influenced by the ferromagnetic precession of ferrite cuboids when a certain magnetic field is applied. The effective permittivity of the metamaterial can be tuned by modifying the applied magnetic field. A good agreement between experimental and simulated results is demonstrated, which confirms that these metamaterials can be used for tunable microwave devices.

7. Tunable Dielectric Properties of Ferrite-Dielectric Based Metamaterial

PubMed Central

Bi, K.; Huang, K.; Zeng, L. Y.; Zhou, M. H.; Wang, Q. M.; Wang, Y. G.; Lei, M.

2015-01-01

A ferrite-dielectric metamaterial composed of dielectric and ferrite cuboids has been investigated by experiments and simulations. By interacting with the electromagnetic wave, the Mie resonance can take place in the dielectric cuboids and the ferromagnetic precession will appear in the ferrite cuboids. The magnetic field distributions show the electric Mie resonance of the dielectric cuboids can be influenced by the ferromagnetic precession of ferrite cuboids when a certain magnetic field is applied. The effective permittivity of the metamaterial can be tuned by modifying the applied magnetic field. A good agreement between experimental and simulated results is demonstrated, which confirms that these metamaterials can be used for tunable microwave devices. PMID:25993433

8. The dielectric breakdown limit of silicone dielectric elastomer actuators

NASA Astrophysics Data System (ADS)

Gatti, Davide; Haus, Henry; Matysek, Marc; Frohnapfel, Bettina; Tropea, Cameron; Schlaak, Helmut F.

2014-02-01

Soft silicone elastomers are used in a generation of dielectric elastomer actuators (DEAs) with improved actuation speed and durability compared to the commonly used, highly viscoelastic polyacrylate 3M VHB™ films. The maximum voltage-induced stretch of DEAs is ultimately limited by their dielectric breakdown field strength. We measure the dependence of dielectric breakdown field strength on thickness and stretch for a silicone elastomer, when voltage-induced deformation is prevented. The experimental results are combined with an analytic model of equi-biaxial actuation to show that accounting for variable dielectric field strength results in different values of optimal pre-stretch and thickness that maximize the DEA actuation.

9. Metal filled porous carbon

DOEpatents

Gross, Adam F.; Vajo, John J.; Cumberland, Robert W.; Liu, Ping; Salguero, Tina T.

2011-03-22

A porous carbon scaffold with a surface and pores, the porous carbon scaffold containing a primary metal and a secondary metal, where the primary metal is a metal that does not wet the surface of the pores of the carbon scaffold but wets the surface of the secondary metal, and the secondary metal is interspersed between the surface of the pores of the carbon scaffold and the primary metal.

10. Long-range Tamm surface plasmons supported by graphene-dielectric metamaterials

NASA Astrophysics Data System (ADS)

Hajian, Hodjat; Caglayan, Humeyra; Ozbay, Ekmel

2017-01-01

Considering the Ohmic losses of graphene in the calculations and by obtaining exact dispersion relations of the modes, we theoretically study propagation and localization characteristics of Tamm surface plasmons supported by terminated graphene metamaterials. The metamaterials are composed of alternating layers of graphene and dielectric with subwavelength periods. We also examine the Tamm modes within the framework of long-wavelength approximation. It is shown that, in case the Ohmic losses of the graphene layers are taken into account, surface plasmons are not supported in a long-wavelength region, in which the graphene-dielectric multilayer structure behaves as a hyperbolic metamaterial. We prove that, when the metamaterial is truncated with air, by choosing sufficiently thick but still subwavelength dielectric layers, i.e., d = 300 nm, these surface waves will have a moderate propagation (localization) length that is comparable with those of a single layer of graphene. On the other hand, in case a miniaturized graphene metamaterial (10 < d(nm) < 100) is truncated by a thick cap layer (dcap = 5d) with ɛcap > ɛdielectric, it is possible to considerably improve the propagation and localization characteristics of the Tamm modes supported by the system within the 5.5-50 THz range of frequency, as compared to a single layer of graphene.

11. Subterahertz dielectric relaxation in lead-free Ba(Zr,Ti)O3 relaxor ferroelectrics

NASA Astrophysics Data System (ADS)

Wang, D.; Bokov, A. A.; Ye, Z.-G.; Hlinka, J.; Bellaiche, L.

2016-04-01

Relaxors are complex materials with unusual properties that have been puzzling the scientific community since their discovery. The main characteristic of relaxors, that is, their dielectric relaxation, remains unclear and is still under debate. The difficulty to conduct measurements at frequencies ranging from ~=1 GHz to ~=1 THz and the challenge of developing models to capture their complex dynamical responses are among the reasons for such a situation. Here, we report first-principles-based molecular dynamic simulations of lead-free Ba(Zr0.5Ti0.5)O3, which allows us to obtain its subterahertz dynamics. This approach reproduces the striking characteristics of relaxors including the dielectric relaxation, the constant-loss behaviour, the diffuse maximum in the temperature dependence of susceptibility, the substantial widening of dielectric spectrum on cooling and the resulting Vogel-Fulcher law. The simulations further relate such features to the decomposed dielectric responses, each associated with its own polarization mechanism, therefore, enhancing the current understanding of relaxor behaviour.

12. Dielectric Nonlinear Transmission Line (Postprint)

DTIC Science & Technology

2011-12-01

Technical Paper 3. DATES COVERED (From - To) 2011 4. TITLE AND SUBTITLE Dielectric Nonlinear Transmission Line (POSTPRINT) 5a. CONTRACT NUMBER...14. ABSTRACT A parallel plate nonlinear transmission line (NLTL) was constructed. Periodic loading of nonlinear dielectric slabs provides the...846-9101 Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. 239.18 Dielectric Nonlinear Transmission Line David M. French, Brad W. Hoff

13. Dielectric properties of lunar surface

NASA Astrophysics Data System (ADS)

Yushkova, O. V.; Kibardina, I. N.

2017-03-01

Measurements of the dielectric characteristics of lunar soil samples are analyzed in the context of dielectric theory. It has been shown that the real component of the dielectric permittivity and the loss tangent of rocks greatly depend on the frequency of the interacting electromagnetic field and the soil temperature. It follows from the analysis that one should take into account diurnal variations in the lunar surface temperature when interpreting the radar-sounding results, especially for the gigahertz radio range.

14. Metrology development and mechanical reinforcement for novel low-k dielectrics

NASA Astrophysics Data System (ADS)

Yang, Dan

Considerable attention has been focused on exploring novel low dielectric constant (k) materials to replace the traditional interconnect dielectric material, silicon dioxide, in order to reduce capacitive signal delay from the back end of line (BEOL) and power consumption. Among all ultra low-k (ULK) materials, SiCOH is the most popular and mature material for integration. It has been generally agreed that incorporating porosity is necessary to decrease the dielectric constant below 2.5 for future technology nodes. However, while incorporation of carbon and porosity benefit dielectric properties, the mechanical properties degrade simultaneously. Therefore, material composition, matrix structure and porosity must be carefully controlled to optimize dielectric properties without sacrificing mechanical robustness. As porous low-k dielectric thin films begin to be investigated, new challenges are posed on metrologies. When mechanical properties are evaluated using nanoindentation, the 'substrate effect', which evolves from the contribution of elastic strain of substrate, causes an overestimation of film intrinsic mechanical properties. The use of cube corner tip instead of Berkovich tip is proposed to minimize the substrate effect. The experimental results show that the use of cube corner tip enhances the critical depth from below 10% of the film thickness to 40%. The characterization of porosity of porous low-k dielectric films is a challenge posed on metrologies due to the limited sampling volume. The application of three non-destructive porosimetry techniques, Positron Annihilation Lifetime Spectroscopy (PALS), Ellipsometric Porosimetry (EP) and X-ray Reflectivity (XRR) to characterize xviii porous low-k thin films are examined. The advantages and limitations of each technique, especially the sensitivity to pore interconnectivity, are discussed. The optimization of SiCOH low-k dielectrics are conducted from two aspects; optimization of deposition conditions and

15. Nonthermal combined ultraviolet and vacuum-ultraviolet curing process for organosilicate dielectrics

NASA Astrophysics Data System (ADS)

Zheng, H.; Guo, X.; Pei, D.; Li, W.; Blatz, J.; Hsu, K.; Benjamin, D.; Lin, Y.-H.; Fung, H.-S.; Chen, C.-C.; Nishi, Y.; Shohet, J. L.

2016-06-01

Porous SiCOH films are of great interest in semiconductor fabrication due to their low-dielectric constant properties. Post-deposition treatments using ultraviolet (UV) light on organosilicate thin films are required to decompose labile pore generators (porogens) and to ensure optimum network formation to improve the electrical and mechanical properties of low-k dielectrics. The goal of this work is to choose the best vacuum-ultraviolet photon energy in conjunction with vacuum ultraviolet (VUV) photons without the need for heating the dielectric to identify those wavelengths that will have the most beneficial effect on improving the dielectric properties and minimizing damage. VUV irradiation between 8.3 and 8.9 eV was found to increase the hardness and elastic modulus of low-k dielectrics at room temperature. Combined with UV exposures of 6.2 eV, it was found that this "UV/VUV curing" process is improved compared with current UV curing. We show that UV/VUV curing can overcome drawbacks of UV curing and improve the properties of dielectrics more efficiently without the need for high-temperature heating of the dielectric.

16. Inspection of Asian Lacquer Substructures by Terahertz Time-Domain Imaging (THz-TDI)

NASA Astrophysics Data System (ADS)

Dandolo, Corinna Ludovica Koch; Fukunaga, Kaori; Kohzuma, Yoshei; Kiriyama, Kyoko; Matsuda, Kazutaka; Jepsen, Peter Uhd

2016-11-01

Lacquering is considered one of the most representative Asian artistic techniques. While the decorative part of lacquerwares is the lacquer itself, their substructures serve as the backbone of the object itself. Very little is known about these hidden substructures. Since lacquerwares are mostly composed of organic materials, such as urushi, wood, carbon black, and fabrics which are very X-ray transparent, standard X-ray radiography has some problems in achieving clear X-ray radiographic images. Therefore, we wanted to contribute to the understanding of the lacquer manufacturing technique by inspecting the substructures of Asian lacquerwares by means of THz time-domain imaging (THz-TDI). Three different kinds of Asian lacquerwares were examined by THz-TDI, and the outcomes have been compared with those obtained by standard X-radiography. THz-TDI provides unique information on lacquerwares substructures, aiding in the comprehension of the manufacturing technology yielding to these precious artefacts.

17. Video rate imaging at 1.5 THz via frequency upconversion to the near-IR

NASA Astrophysics Data System (ADS)

Tekavec, Patrick F.; Kozlov, Vladimir G.; McNee, Ian; Lee, Yun-Shik; Vodopyanov, Konstantin

2015-05-01

We demonstrate video rate THz imaging in both reflection and transmission by frequency upconverting the THz image to the near-IR. In reflection, the ability to resolve images generated at different depths is shown. By mixing the THz pulses with a portion of the fiber laser pump (1064 nm) in a quasi-phase matched gallium arsenide crystal, distinct sidebands are observed at 1058 nm and 1070 nm, corresponding to sum and difference frequency generation of the pump pulse with the THz pulse. By using a polarizer and long pass filter, the strong pump light can be removed, leaving a nearly background free signal at 1070 nm. We have obtained video rate images with spatial resolution of 1mm and field of view ca. 20 mm in diameter without any post processing of the data.

18. Detection and identification of explosive RDX by THz diffuse reflection spectroscopy

NASA Astrophysics Data System (ADS)

Liu, Hai-Bo; Chen, Yunqing; Bastiaans, Glenn J.; Zhang, X.-C.

2006-01-01

The reflection spectrum of the explosive RDX was acquired from a diffuse reflection measurement using a THz time-domain spectroscopy system in combination with a diffuse reflectance accessory. By applying the Kramers-Kronig transform to the reflection spectrum, the absorption spectrum (0.2-1.8 THz) was obtained. It agrees with the result from a transmission measurement and distinguishes RDX from other materials. The effect of the reference spectrum was examined by using both a Teflon pellet and a copper plate as references. The strong absorption of RDX at 0.82 THz allowed it to be identified by the diffuse reflection measurement even when the RDX sample was covered with certain optically opaque materials. Our investigation demonstrates that THz technique is capable of detecting and identifying hidden RDX-related explosives in a diffuse reflection mode, which is crucial for the standoff detection in the real world applications.

19. Inspection of Asian Lacquer Substructures by Terahertz Time-Domain Imaging (THz-TDI)

NASA Astrophysics Data System (ADS)

Dandolo, Corinna Ludovica Koch; Fukunaga, Kaori; Kohzuma, Yoshei; Kiriyama, Kyoko; Matsuda, Kazutaka; Jepsen, Peter Uhd

2017-04-01

Lacquering is considered one of the most representative Asian artistic techniques. While the decorative part of lacquerwares is the lacquer itself, their substructures serve as the backbone of the object itself. Very little is known about these hidden substructures. Since lacquerwares are mostly composed of organic materials, such as urushi, wood, carbon black, and fabrics which are very X-ray transparent, standard X-ray radiography has some problems in achieving clear X-ray radiographic images. Therefore, we wanted to contribute to the understanding of the lacquer manufacturing technique by inspecting the substructures of Asian lacquerwares by means of THz time-domain imaging (THz-TDI). Three different kinds of Asian lacquerwares were examined by THz-TDI, and the outcomes have been compared with those obtained by standard X-radiography. THz-TDI provides unique information on lacquerwares substructures, aiding in the comprehension of the manufacturing technology yielding to these precious artefacts.

20. Kinetic inductance driven nanoscale 2D and 3D THz transmission lines

PubMed Central

Mousavi, S. Hossein; Williamson, Ian A. D.; Wang, Zheng

2016-01-01

We examine the unusual dispersion and attenuation of transverse electromagnetic waves in the few-THz regime on nanoscale graphene and copper transmission lines. Conventionally, such propagation has been considered to be highly dispersive, due to the RC time constant-driven voltage diffusion below 1 THz and plasmonic effects at higher optical frequencies. Our numerical modeling across the microwave, THz, and optical frequency ranges reveals that the conductor kinetic inductance creates an ultra-broadband linear-dispersion and constant-attenuation region in the THz regime. This so-called LC region is an ideal characteristic that is known to be absent in macro-scale transmission lines. The kinetic-LC frequency range is dictated by the structural dimensionality and the free-carrier scattering rate of the conductor material. Moreover, up to 40x wavelength reduction is observed in graphene transmission lines. PMID:27137628

1. THz generation by self-focusing of hollow Gaussian laser beam in magnetised plasma

NASA Astrophysics Data System (ADS)

Hussain, Saba; Singh, Monika; Kishor Singh, Ram; Sharma, R. P.

2014-09-01

A scheme of terahertz (THz) generation is proposed by the self-focusing of a high-power laser beam having hollow Gaussian intensity profile in a collissionless magnetized plasma, where ponderomotive nonlinearity is operative. THz waves are resonantly excited at the difference frequency of laser and electron plasma wave (EPW) satisfying the proper phase matching conditions. In this paper first we have investigated the filamentation of the circularly polarized hollow Gaussian beam (HGB) propagating parallel to the direction of a static background magnetic field within the paraxial approximation, subsequently this filamented HG laser beam interplay with the electron plasma wave to generate a nonlinear current in the transverse direction, thereby producing THz radiations. The intensity of the emitted radiations are found to be highly sensitive to the order of the HGB. For the current scheme the power level of THz wave comes out to be ˜ 0.05 gigawatts.

2. Intense Nanosecond-Pulsed Cavity-Dumped Laser Radiation at 1.04 THz

NASA Astrophysics Data System (ADS)

Wilson, Thomas

2013-03-01

We report first results of intense far-infrared (FIR) nanosecond-pulsed laser radiation at 1.04 THz from a previously described[2] cavity-dumped, optically-pumped molecular gas laser. The gain medium, methyl fluoride, is pumped by the 9R20 line of a TEA CO2 laser[3] with a pulse energy of 200 mJ. The THz laser pulses contain of 30 kW peak power in 5 nanosecond pulse widths at a pulse repetition rate of 10 Hz. The line width, measured by a scanning metal-mesh FIR Fabry-Perot interferometer, is 100 MHz. The novel THz laser is being used in experiments to resonantly excite coherent ns-pulsed 1.04 THz longitudinal acoustic phonons in silicon doping-superlattices. The research is supported by NASA EPSCoR NNX11AM04A and AFOSR FA9550-12-1-0100 awards.

3. The THz fingerprint spectra of the active ingredients of a TCM medicine: Herba Ephedrae

NASA Astrophysics Data System (ADS)

Ma, Shihua; Liu, Guifeng; Zhang, Peng; Song, Xiyu; Ji, Te; Wang, Wenfeng

2008-12-01

In this paper, THz-TDS has been used to measure the spectral properties of two active ingredients of Herba Ephedrae: ephedrine and pseudoephedrine, which exist in hydrochloride salts. The THz spectra of the sole-ingredient, twoingredient and three-ingredient compounds are studied. We obtained the finger-print spectra of the net active ingredients of the medicine, and also measured the mixtures of by two or three active ingredients at the different ratios. At the same time, theoretical analysis and quantitative analysis is applied to foretell the different THz spectra, identify the ingredients and infer the contents of principal components in samples. The THz spectroscopy is a potential and promising technique in evaluating and inspecting the quality of the drugs in the TCM field.

4. 3D printed low-loss THz waveguide based on Kagome photonic crystal structure.

PubMed

Yang, Jing; Zhao, Jiayu; Gong, Cheng; Tian, Haolin; Sun, Lu; Chen, Ping; Lin, Lie; Liu, Weiwei

2016-10-03

A low-loss hollow core terahertz waveguide based on Kagome photonic crystal structure has been designed and fabricated by 3D printing. The 3D printed waveguide has been characterized by using THz time-domain spectroscopy. The results demonstrate that the obtained waveguide features average power propagation loss of 0.02 cm-1 for 0.2-1.0 THz (the minimum is about 0.002 cm-1 at 0.75 THz). More interesting, it could be simply mechanically spliced without any additional alignment, while maintaining the excellent performance. The 3D printing technique will be a promising solution to fabricate Kagome THz waveguide with well controllable characteristics and low cost.

5. Porous silicon-based rugate filters.

PubMed

Lorenzo, Eduardo; Oton, Claudio J; Capuj, Néstor E; Ghulinyan, Mher; Navarro-Urrios, Daniel; Gaburro, Zeno; Pavesi, Lorenzo

2005-09-10

We report an experimental study of porous silicon-based rugate filters. We performed filter apodization, following a half-apodization approach, which successfully attenuated the sidelobes at both sides of the photonic stop band. We achieved successful reduction of interference ripples through the insertion of index-matching layers on the first and last interfaces. An apodized dielectric mirror and a rugate filter are compared: Appreciable differences in the harmonic presence and stop-band performance were observed and are commented on. Bandwidth control when index contrast is modified is also demonstrated. Finally, the possibility of combining different rugate filter designs to attain more complex responses is demonstrated by the achievement of a multi-stop-band filter. Numerical calculations for design optimization and comparison with experimental data are reported too.

6. CH3D photomixing spectroscopy up to 2.5 THz: New set of rotational and dipole parameters, first THz self-broadening measurements

NASA Astrophysics Data System (ADS)

Bray, Cédric; Cuisset, Arnaud; Hindle, Francis; Bocquet, Robin; Mouret, Gaël; Drouin, Brian J.

2017-03-01

Several previously unmeasured transitions of 12CH3D have been recorded by a terahertz photomixing continuous-wave spectrometer up to QR(10) branch at 2.5 THz. An improved set of rotational constants has been obtained utilizing a THz frequency metrology based on a frequency comb that achieved an averaged frequency position better than 150 kHz on more than fifty ground-state transitions. A detailed analysis of the measured line intensities was undertaken using the multispectrum fitting program and has resulted in a determination of new dipole moment parameters. Measurements at different pressures of the QR(7) transitions provide the first determination of self-broadening coefficients from pure rotational CH3D lines. The THz rotational measurements are consistent with IR rovibrational data but no significant vibrational dependence of self-broadening coefficient may be observed by comparison.

7. A coherent frequency-domain THz spectrometer with a signal-to-noise ratio of 60 dB at 1 THz

NASA Astrophysics Data System (ADS)

Demers, Joseph R.; Logan, Ronald T., Jr.; Bergeron, Normand J.; Brown, Elliot R.

2008-04-01

A terahertz frequency domain spectrometer is implemented using two ErAs:GaAs photomixers in a highly compact configuration, utilizing all solid-state components and no moving parts. Digital signal processing electronics provide precise frequency control and yield ~200 MHz accuracy of the THz signal frequency. Continuous frequency sweeping is demonstrated with better than 1 GHz resolution from 200 GHz to 1.85 THz. The coherent detection sensitivity is shown to be in good agreement with previous theoretical predictions and yields a signal-to-noise ratio of 80 dB*Hz at 200 GHz and 60 dB*Hz at 1 THz through a path length in air of one foot.

8. IR/THz Double Resonance Spectroscopy Approach for Remote Chemical Detection at Atmospheric Pressure

NASA Astrophysics Data System (ADS)

Tanner, Elizabeth A.; Phillips, Dane J.; De Lucia, Frank C.; Everitt, Henry O.

2013-06-01

A remote sensing methodology based on infrared/terahertz (IR/THz) double resonance (DR) spectroscopy is shown to overcome limitations traditionally associated with either IR or THz spectroscopic approaches for detecting trace gases in an atmosphere. The applicability of IR/THz DR spectroscopy is explored by estimating the IR and THz power requirements for detecting a 100 part-per-million-meter cloud of methyl fluoride, methyl chloride, or methyl bromide at ranges up to 1km in three atmospheric windows below 0.3 THz. These prototypical molecules are used to ascertain the dependence of the DR signal-to-noise ratio on IR and THz beam power. A line-tunable CO_2 laser with 100 ps pulse duration generates a DR signature in four rotational transitions on a time scale commensurate with collisional relaxations caused by atmospheric N_2 and O_2. A continuous wave THz beam is frequency tuned to probe one of these rotational transitions so that laser-induced absorption variations in the analyte cloud are detected as temporal power fluctuations synchronized with the laser pulses. A combination of molecule-specific physics and scenario-dependent atmospheric conditions are used to predict the signal-to-noise ratio (SNR) for detecting an analyte as a function of cloud column density. A methodology is presented by which the optimal IR/THz pump/probe frequencies are identified. These estimates show the potential for low concentration chemical detection in a challenging atmospheric scenario with currently available or near term hardware components.

9. 20 THz broadband generation using semi-insulating GaAs interdigitated photoconductive antennas.

PubMed

Hale, P J; Madeo, J; Chin, C; Dhillon, S S; Mangeney, J; Tignon, J; Dani, K M

2014-10-20

We demonstrate broadband (20 THz), high electric field, terahertz generation using large area interdigitated antennas fabricated on semi-insulating GaAs. The bandwidth is characterized as a function of incident pulse duration (15-35 fs) and pump energy (2-30 nJ). Broadband spectroscopy of PTFE is shown. Numerical Drude-Lorentz simulations of the generated THz pulses are performed as a function of the excitation pulse duration, showing good agreement with the experimental data.

10. Generation of THz Radiation by Excitation of InAs with a Free Electron Laser

SciTech Connect

Mashiko Tani; Shunsuke Kono; Ping Gu; Kiyomi Sakai; Mamoru Usami; Michelle D. Shinn; Joseph F. Gubeli; George Neil; Jingzhou Xu; Roland Kersting; X.-C. Zhang

2001-01-01

Terahertz (THz) radiation is generated by exciting an un-doped InAs wafer with a femtosecond free-electron laser (FEL) at the Thomas Jefferson National Accelerator Facility. A microwatt level of THz radiation is detected from the unbiased InAs emitter when it is excited with the femtosecond FEL pulses operated at a wavelength of 1.06 {mu}-m and 10 W average power.

11. Widely tuneable ultra stable 1W two color THz laser source

NASA Astrophysics Data System (ADS)

Stry, Sandra; Sacher, Joachim R.

2007-02-01

Coherent cw-THz-radiation allows access to new applications in the field of medicine, industrial process control, data communication and security applications. Major advantages of radiation in this spectral range are that it penetrates through e.g. plastics but is strongly reflected by metals and that molecules show distinct and distinguishable spectra so that a selective sensing of single species is possible. However, existing THz-sources are either very bulky or expensive. THz sources can require cryogenic temperatures or emit only low power radiation. Furthermore the setup is often very complicated and sensitive so that field measurements are not possible. Generation of THz radiation based on the technology of frequency mixing requires laser radiation with a difference frequency in the order of 0.1-2 THz. Due to the low efficiency of frequency mixers, high optical power is required for pumping frequency mixers. Furthermore, the small efficiency requires short optical pulses for avoiding a high heat dissipation of the frequency mixers. We investigated an ultra stable 1W two colour THz pump source for the generation of a THz beat signal with rapid single mode tuning over several THz. The system consist of a fixed wavelength and a motorized tuneable laser pump sources which are optical amplified within a pulse operation module. One laser is stabilized to an atomic reference while the other is locked to an optical cavity which can be tuned continuously. This signal is pump source for a state of the art frequency mixer, which is typically realized as LT-GaAs crystal with an antenna design.

12. Structured Nanowires for Spectra-Tuned and Spectra-Multiplexed Sensing THZ Generation

DTIC Science & Technology

2015-04-08

ofthe Spoosored Projects Box 1929, 164 Angell Street, Providence, RI 02912-9002 19. .. AND 110.: "u~o . ···-· Adaptive Sensing aod GHz-THz-Speed...less processes . If successful, the project will help advance the technology for IR sensing and THz generation, by providing a new platform with spectral...temperature, solvothermal reaction process without a template [3]. 3. In a theoretical study we reported [4] on the geometry-and size-dependent effects

13. Characteristics and development of the coherent synchrotron radiation sources for THz spectroscopy

NASA Astrophysics Data System (ADS)

Barros, J.; Evain, C.; Roussel, E.; Manceron, L.; Brubach, J.-B.; Tordeux, M.-A.; Couprie, M.-E.; Bielawski, S.; Szwaj, C.; Labat, M.; Roy, P.

2015-09-01

We report on the characteristics of coherent synchrotron radiation (CSR) as a source for spectroscopy. The optimization of the source and the resulting figures of merits in terms of flux, signal to noise, spatial distribution and spectral and temporal distribution are presented together with a spectroscopic application. The emission of THz during the slicing operation is also described. The conclusion opens up perspectives made possible by the availability of this intense and stable THz source.

14. Spontaneous Energy Concentration in Energetic Molecules, Interfaces and Composites: Response to Ultrasound and THz Radiation

DTIC Science & Technology

2015-12-21

Technical Report 3. DATES COVERED (From - To) -1 Mar 2011 to 30 Sept 2015 4. TITLE AND SUBTITLE Spontaneous energy concentration in energetic...SUPPLEMENTARY NOTES 14. ABSTRACT The effects of weak energies , THz and ultrasound, on energetic materials, was studied experimentally using laser...vibrational spectroscopies and time-resolved thermal imaging microscopy. 15. SUBJECT TERMS Ultrasound, THz radiation, energetic materials, hot spots, energy

15. CMP Control of Multi-Layer Inter-Layer Dielectrics (ILD) using X-ray Reflectivity

SciTech Connect

Bryant, Ross E.; Porter, Hethel; Gallegos, Jesus; O'Dell, Jeremy; Agnihotri, Dileep

2007-09-26

Thin sacrificial films are used as cap layer in the back-end semiconductor processing for protecting the bulk porous inter-layer low-k dielectric during the CMP process. The existing optical measurement techniques struggle to separate these thin films from the bulk low-k due to very similar optical coefficients. Glancing angle x-ray reflectivity is well suited for separation of thin sacrificial film and bulk dielectric film as x-ray reflectivity depends strongly on changes in electron densities for two materials. This paper discusses the x-ray reflectivity technique and its applications for measurement of low-k stack and sacrificial oxide post CMP.

16. Extremely low material loss and dispersion flattened TOPAS based circular porous fiber for long distance terahertz wave transmission

NASA Astrophysics Data System (ADS)

Islam, Md. Saiful; Sultana, Jakeya; Rana, Sohel; Islam, Mohammad Rakibul; Faisal, Mohammad; Kaijage, Shubi F.; Abbott, Derek

2017-03-01

In this paper, we present a porous-core circular photonic crystal fiber (PC-CPCF) with ultra-low material loss for efficient terahertz wave transmission. The full vector finite element method with an ideally matched layer boundary condition is used to characterize the wave guiding properties of the proposed fiber. At an operating frequency of 1 THz, simulated results exhibit an extremely low effective material loss of 0.043 cm-1, higher core power fraction of 47% and ultra-flattened dispersion variation of 0.09 ps/THz/cm. The effects of important design properties such as single mode operation, confinement loss and effective area of the fiber are investigated in the terahertz regime. Moreover, the proposed fiber can be fabricated using the capillary stacking or sol-gel technique and be useful for long distance transmission of terahertz waves.

17. A Study of Electron and Phonon Dynamics by Broadband Two-Dimensional THz Time-Domain Spectroscopy

NASA Astrophysics Data System (ADS)

Fu, Zhengping

Terahertz (THz) wave interacts with semiconductors in many ways, such as resonant excitation of lattice vibration, intraband transition and polaron formation. Different from the optical waves, THz wave has lower photon energy (1 THz = 4.14 meV) and is suitable for studying dynamics of low-energy excitations. Recently the studies of the interaction of THz wave and semiconductors have been extending from the linear regime to the nonlinear regime, owing to the advance of the high-intensity THz generation and detection methods. Two-dimensional (2D) spectroscopy, as a useful tool to unravel the nonlinearity of materials, has been well developed in nuclear magnetic resonance and infrared region. However, the counterpart in THz region has not been well developed and was only demonstrated at frequency around 20 THz due to the lack of intense broadband THz sources. Using laser-induced plasma as the THz source, we developed collinear broadband 2D THz time-domain spectroscopy covering from 0.5 THz to 20 THz. Broadband intense THz pulses emitted from laser-induced plasma provide access to a variety of nonlinear properties of materials. Ultrafast optical and THz pulses make it possible to resolve the transient change of the material properties with temporal resolution of tens of femtoseconds. This thesis focuses on the linear and nonlinear interaction of the THz wave with semiconductors. Since a great many physical processes, including vibrational motion of lattice and plasma oscillation, has resonant frequency in the THz range, rich physics can be studies in our experiment. The thesis starts from the linear interaction of the THz wave with semiconductors. In the narrow band gap semiconductor InSb, the plasma absorption edge, Restrahlen band and dispersion of polaritons are observed. The nonlinear response of InSb in high THz field is verified in the frequency-resolved THz Z-scan experiment. The third harmonic generations due to the anharmonicity of plasma oscillation and the

18. THz behavior of indium-tin-oxide films on p-Si substrates

SciTech Connect

Brown, E. R. Zhang, W-D.; Chen, H.; Mearini, G. T.

2015-08-31

This paper reports broadband THz free-space transmission measurements and modeling of indium-tin-oxide (ITO) thin films on p-doped Si substrates. Two such samples having ITO thickness of 50 and 100 nm, and DC sheet conductance 260 and 56 Ω/sq, respectively, were characterized between 0.2 and 1.2 THz using a frequency-domain spectrometer. The 50-nm-film sample displayed very flat transmittance over the 1-THz bandwidth, suggesting it is close to the critical THz sheet conductance that suppresses multi-pass interference in the substrate. An accurate transmission-line-based equivalent circuit is developed to explain the effect, and then used to show that the net reflectivity and absorptivity necessarily oscillate with frequency. This has important implications for the use of thin-film metallic coupling layers on THz components and devices, such as detectors and sources. Consistent with previous reported results, the sheet conductance that best fits the THz transmittance data is roughly 50% higher than the DC values for both samples.

19. Identification of explosive media using spectrum dynamics under the action of a THz pulse

NASA Astrophysics Data System (ADS)

Trofimov, Vyacheslav A.; Varentsova, Svetlana A.; Chen, Jian; Zhang, Xi-Cheng

2009-09-01

A method of THz spectral dynamics analysis (SDA) of medium response in the THz and GHz ranges, which was developed by us in previous papers for detection and identification of materials, is used for the treatment of experimentally measured signals, passed through selected explosives, including those hidden under covering materials. This technique is based on the window sliding method and on restoration of the THz pulse. It allows researchers to follow the dynamics of many spectral lines in one set of measurements simultaneously and to obtain the full information about the spectrum dynamics of the THz pulse. Relaxation time of rotational transitions, for example, can be determined too. This information gives an opportunity to detect and identify materials despite the similarity in their THz spectra-which may be identical. We show that the spectrum dynamics of THz pulses, passed through the explosives hidden under plastic, cotton and leather barriers-covers, differ widely for these media despite little difference in their spectra. Consequently, our method allows for detection and identification of the hidden explosives with high probability.

20. Quantum-dot based ultrafast photoconductive antennae for efficient THz radiation

NASA Astrophysics Data System (ADS)

Gorodetsky, Andrei; Bazieva, Natalia; Rafailov, Edik U.

2016-03-01

Here we overview our work on quantum dot based THz photoconductive antennae, capable of being pumped at very high optical intensities of higher than 1W optical mean power, i.e. about 50 times higher than the conventional LT-GaAs based antennae. Apart from high thermal tolerance, defect-free GaAs crystal layers in an InAs:GaAs quantum dot structure allow high carrier mobility and ultra-short photo carrier lifetimes simultaneously. Thus, they combine the advantages and lacking the disadvantages of GaAs and LT-GaAs, which are the most popular materials so far, and thus can be used for both CW and pulsed THz generation. By changing quantum dot size, composition, density of dots and number of quantum dot layers, the optoelectronic properties of the overall structure can be set over a reasonable range-compact semiconductor pump lasers that operate at wavelengths in the region of 1.0 μm to 1.3 μm can be used. InAs:GaAs quantum dot-based antennae samples show no saturation in pulsed THz generation for all average pump powers up to 1W focused into 30 μm spot. Generated THz power is super-linearly proportional to laser pump power. The generated THz spectrum depends on antenna design and can cover from 150 GHz up to 1.5 THz.

1. Identification of explosives and drugs and inspection of material defects with THz radiation

NASA Astrophysics Data System (ADS)

Zhang, Cunlin; Mu, Kaijun; Jiang, Xue; Jiao, Yueying; Zhang, Liangliang; Zhou, Qingli; Zhang, Yan; Shen, Jingling; Zhao, Guoshong; Zhang, X.-C.

2008-03-01

We report the sensing of explosive materials and illicit drugs by using terahertz time-domain spectroscopy (THz-TDS) and imaging. Several explosive materials, such as γ-HNIW, RDX, 2,4-DNT, TNT, Nitro-aniline, and illicit drugs, such as methamphetamine (MA) etc were researched here. Non-destructive testing, as one of the major applications of THz imaging, can be applied to an area of critical need: the testing of aerospace materials. Composite materials such as carbon fiber are widely used in this industry. The nature of their use requires technologies that are able to differentiate between safe and unsafe materials, due to either manufacturing tolerance or damage acquired while in use. In this paper, we discuss the applicability of terahertz (THz) imaging systems to this purpose, focusing on graphite fiber composite materials, carbon silicon composite materials and so on. We applied THz imaging technology to evaluate the fire damage to a variety of carbon fiber composite samples. Major carbon fiber materials have polarization-dependent reflectivity in THz frequency range, and we show how the polarization dependence changes versus the burned damage level. Additionally, time domain information acquired through a THz time-domain spectroscopy (TDS) system provides further information with which to characterize the damage. We also detect fuel tank insulation foam panel defects with pulse and continuous-wave (CW) terahertz system.

2. A THz spectrometer combining the free electron laser FLARE with 33 T magnetic fields

NASA Astrophysics Data System (ADS)

Ozerov, M.; Bernáth, B.; Kamenskyi, D.; Redlich, B.; van der Meer, A. F. G.; Christianen, P. C. M.; Engelkamp, H.; Maan, J. C.

2017-02-01

The free electron laser Free electron Laser for Advanced spectroscopy and high Resolution Experiments (FLARE) at the FELIX Laboratory generates powerful radiation in the frequency range of 0.3-3 THz. This light, in combination with 33 T Bitter magnets at the High Field Magnet Laboratory, provides the unique opportunity to perform THz magneto spectroscopy with light intensities many orders of magnitude higher than provided by conventional sources. The performance of the THz spectrometer is measured via high-field electron spin resonance (ESR) in the paramagnetic benchmark system 2,2-diphenyl-1-picrylhydrazyl (DPPH). The narrow ESR linewidth of DPPH allows us to resolve a fine structure with 3 GHz spacing, demonstrating a considerable coherence of the individual THz micropulses of FLARE. The spectral resolution Δ ν / ν is better than 0.1%, which is an order of magnitude higher than typical values for a rf-linac based free electron laser. The observed coherence of the high power THz micropulses is a prerequisite for resonant control of matter, such as THz electron spin echo spectroscopy.

3. Biological effects of in vitro THz radiation exposure in human foetal fibroblasts.

PubMed

De Amicis, Andrea; Sanctis, Stefania De; Cristofaro, Sara Di; Franchini, Valeria; Lista, Florigio; Regalbuto, Elisa; Giovenale, Emilio; Gallerano, Gian Piero; Nenzi, Paolo; Bei, Roberto; Fantini, Massimo; Benvenuto, Monica; Masuelli, Laura; Coluzzi, Elisa; Cicia, Cristina; Sgura, Antonella

2015-11-01

In recent years, terahertz (THz) radiation has been widely used in a variety of applications: medical, security, telecommunications and military areas. However, few data are available on the biological effects of this type of electromagnetic radiation and the reported results, using different genetic or cellular assays, are quite discordant. This multidisciplinary study focuses on potential genotoxic and cytotoxic effects, evaluated by several end-points, associated with THz radiation. For this purpose, in vitro exposure of human foetal fibroblasts to low frequency THz radiation (0.1-0.15THz) was performed using a Compact Free Electron Laser. We did not observe an induction of DNA damage evaluated by Comet assay, phosphorylation of H2AX histone or telomere length modulation. In addiction, no induction of apoptosis or changes in pro-survival signalling proteins were detected. Moreover, our results indicated an increase in the total number of micronuclei and centromere positive micronuclei induction evaluated by CREST analysis, indicating that THz radiation could induce aneugenic rather than clastogenic effects, probably leading to chromosome loss. Furthermore, an increase of actin polymerization observed by ultrastructural analysis after THz irradiation, supports the hypothesis that an abnormal assembly of spindle proteins could lead to the observed chromosomal malsegregation.

4. Thin layered drawing media probed by THz time-domain spectroscopy.

PubMed

Tasseva, J; Taschin, A; Bartolini, P; Striova, J; Fontana, R; Torre, R

2016-12-19

Dry and wet drawing materials were investigated by THz time-domain spectroscopy in transmission mode. Carbon-based and iron-gall inks have been studied, some prepared following ancient recipes and others using current synthetic materials; a commercial ink was studied as well. We measured the THz signals on the thin films of liquid inks deposited on polyethylene pellicles, comparing the results with the thick pellets of dried inks blended with polyethylene powder. This study required the implementation of an accurate experimental method and data analysis procedure able to provide a reliable extraction of the material transmission parameters from a structured sample composed of thin layers, down to a thickness of a few tens of micrometers. THz measurements on thin ink layers enabled the determination of both the absorption and the refractive index in an absolute scale in the 0.1-3 THz range, as well as the layer thickness. THz spectroscopic features of a paper sheet dyed by using one of the iron-gall inks were also investigated. Our results showed that THz time-domain spectroscopy enables the discrimination of various inks on different supports, including the application on paper, together with the proper determination of the absorption coefficients and indices of refraction.

5. THz-driven zero-slippage IFEL scheme for phase space manipulation

NASA Astrophysics Data System (ADS)

Curry, E.; Fabbri, S.; Musumeci, P.; Gover, A.

2016-11-01

We describe an inverse free electron laser (IFEL) interaction driven by a near single-cycle THz pulse that is group velocity-matched to an electron bunch inside a waveguide, allowing for a sustained interaction in a magnetic undulator. We discuss the application of this guided-THz IFEL technique for compression of a relativistic electron bunch and synchronization with the external laser pulse used to generate the THz pulse via optical rectification, as well as a laser-driven THz streaking diagnostic with the potential for femtosecond scale temporal resolution. Initial measurements of the THz waveform via an electro-optic sampling based technique confirm the predicted reduction of the group velocity, using a curved parallel plate waveguide, as a function of the varying aperture size of the guide. We also present the design of a proof-of-principle experiment based on the bunch parameters available at the UCLA PEGASUS laboratory. With a 10 {MV} {{{m}}}-1 THz peak field, our simulation model predicts compression of a 6 {MeV} 100 {fs} electron beam by nearly an order of magnitude and a significant reduction of its initial timing jitter. Work supported by DOE grant DE-SC0009914 and NSF grant PHY-1415583.

6. Characterization of a Large-Area Pyroelectric Detector from 300 GHz to 30 THz

NASA Astrophysics Data System (ADS)

Müller, Ralf; Gutschwager, Berndt; Hollandt, Jörg; Kehrt, Mathias; Monte, Christian; Müller, Ralph; Steiger, Andreas

2015-07-01

The national metrology institute of Germany, the Physikalisch-Technische Bundesanstalt (PTB), together with the company Sensor and Lasertechnik (SLT), develops pyroelectric detectors for radiation in the terahertz (THz) spectral range. The intention of this development is to deliver a highly sensitive, accurately calibrated detector for power measurement in the power range of time-domain spectroscopy (TDS) systems. This work reports about a large-area thin-film pyroelectric (TFP) detector applicable within a wide spectral range from 300 GHz to 30 THz and its radiometric characterization by PTB's THz radiation sources. Applying coherent synchrotron radiation from the Metrology Light Source (MLS), laser radiation from a molecular gas laser and blackbody radiation from a water-heated blackbody to this detector reveal its potential to be capable of spanning an even wider THz frequency range than covered by TDS systems. To demonstrate this, its spectral responsivity was measured at different frequencies between 300 GHz and 30 THz by means of those three THz radiation sources.

7. Observation of a different birefringence order at optical and THz frequencies in LBO crystal

NASA Astrophysics Data System (ADS)

Andreev, Yu. M.; Kokh, A. E.; Kokh, K. A.; Lanskii, G. V.; Litvinenko, K.; Mamrashev, A. A.; Molloy, J. F.; Murdin, B.; Naftaly, M.; Nikolaev, N. A.; Svetlichnyi, V. A.

2017-04-01

THz optical properties of lithium borate (LBO) crystals were measured using time-domain spectroscopy (TDS). The LBO crystal samples were of high optical quality and were cut and polished along the <100>, <010> and <001> axes. Two independent measurements were performed in order to confirm the reproducibility and consistency of results. The contradictions in the previously published data on the THz optical properties of LBO were clarified. It was shown that the birefringence order at THz frequencies is nz THz. This is explained in terms of ionic polarizability and is consistent with the fact that the THz absorption coefficient for a wave polarized along the Z-axis is more than an order of magnitude lower than for the X and Y axes. Absorption as low as 0.2 cm-1 was found at frequencies up to 0.5 THz for a wave polarized parallel to the Z-axis. A set of new dispersion equations was designed for the entire transparency range.

8. Comparison of the THz absorption feature in lactose to related saccharides

NASA Astrophysics Data System (ADS)

Bjarnason, Jon E.; Brown, Elliott R.; Korter, Timothy M.

2007-04-01

Solid-state organic compounds such as α-lactose-monohydrate and biotin have been shown to have narrow and intense THz absorption features at room temperature. Interest in lineshapes in the THz region is justified not only for practical reasons, since they are of crucial importance to spectroscopy-based identification of materials, but also because of the information the line-widths contain about the solid-state physics of the materials. The line-width of THz absorption features (generally from lattice vibrations) in solids is excepted to be inversely proportional to the scattering time of optical phonons. The line-width of absorption features might thus have implications on the solid-state physics of the material, in particular, the interaction of phonons and the phonon density of states. We use a continuous wave THz photomixing system to obtain a high resolution spectrum of α-lactose-mohohydrate and analyze two of its lowest-frequency absorption lines. For comparison we measure the transmission spectra of 5 chemically related saccharides: melecitose, trehalose, maltose, cellobiose, and raffinose. Since α-lactose-monohydrate has a stronger and narrower absorption feature than any of its related saccharides, this comparison study is an important step in understanding the mechanism of THz radiation absorption by organic solids and what line-widths to expect in THz spectroscopy.

9. Low Dielectric Polymers

NASA Technical Reports Server (NTRS)

Venumbaka, Sreenivasulu R.; Cassidy, Patrick E.

2002-01-01

This report summarizes results obtained from research funded through Research Cooperative Agreement No. NCC-1-01033-"Low Dielectric Polymers" (from 5/10/01 through 5/09/02). Results are reported in three of the proposed research areas (Tasks 1-3 in the original proposal): (1) Repeat and confirm the preparation and properties of the new alkyl-substituted PEK, 6HC17-PEK, (2) Prepare and evaluate polymers derived from a highly fluorinated monomer, and (3) Prepare and evaluate new silicon and/or fluorine-containing polymers expected to retain useful properties at low temperature.

10. Inorganic optical dielectric films

NASA Astrophysics Data System (ADS)

Woollam, John A.

1996-07-01

Dielectric coatings have been in use for a very long time, yet today they represent a steadily growing wold-wide industry. A wide range of materials, and applications from the near ultraviolet into the infrared are in use, or under development. This paper is a brief survey, including references to the literature, and a discussion of materials diagnostics. Discussed is the microstructure, optical constants and their relationship as determined especially by optical measurements. This paper emphasizes the materials science aspects rather than applications.

11. Boron nitride as two dimensional dielectric: Reliability and dielectric breakdown

SciTech Connect

Ji, Yanfeng; Pan, Chengbin; Hui, Fei; Shi, Yuanyuan; Lanza, Mario; Zhang, Meiyun; Long, Shibing; Lian, Xiaojuan; Miao, Feng; Larcher, Luca; Wu, Ernest

2016-01-04

Boron Nitride (BN) is a two dimensional insulator with excellent chemical, thermal, mechanical, and optical properties, which make it especially attractive for logic device applications. Nevertheless, its insulating properties and reliability as a dielectric material have never been analyzed in-depth. Here, we present the first thorough characterization of BN as dielectric film using nanoscale and device level experiments complementing with theoretical study. Our results reveal that BN is extremely stable against voltage stress, and it does not show the reliability problems related to conventional dielectrics like HfO{sub 2}, such as charge trapping and detrapping, stress induced leakage current, and untimely dielectric breakdown. Moreover, we observe a unique layer-by-layer dielectric breakdown, both at the nanoscale and device level. These findings may be of interest for many materials scientists and could open a new pathway towards two dimensional logic device applications.

12. Optics and cryogenics for the 1.1 THz multi-pixel heterodyne receiver for APEX

NASA Astrophysics Data System (ADS)

Hurtado, Norma; Graf, Urs U.; Adams, Henning; Honingh, C. E.; Jacobs, Karl; Pütz, Patrick; Güsten, Rolf; Stutzki, Jürgen

2014-08-01

The 1.1 THz multi-pixel heterodyne receiver will be mounted in the Nasmyth A cabin of the 12 m APEX telescope on the Chajnantor plateau, 5000 meters altitude in northern Chile. The receiver will cover the spectral window of 1000 - 1080 GHz, where important spectral lines like CO 9-8 at 1036.9 GHz, a tracer of warm and dense gas and OH+ at 1033 GHz and NH+ at 1012.6 GHz, both important for the study of chemical networks in the ISM, are located. The multi-pixel receiver greatly enhances the science output under the difficult observing conditions in this frequency range. Two 9-pixel focal plane sub-arrays on orthogonal polarizations are installed in easily removable cartridges. We developed a new thermal link to connect the cartridges to the cryostat. Our thermal link is an all-metal design: aluminum and Invar. All the optics is fully reflective, thus avoiding the absorption and reflection losses of dielectric lenses and reducing standing waves in the receiver. To guaranty internal optics alignment, we employ a monolithic integrated optics approach for the cold optics and the Focal Plane Unit (FPU) optics modeled after the CHARM (Compact Heterodyne Array Receiver Module) concept. The receiver uses synthesizer-driven solid-state local oscillators (LO) and the mixers will be balanced SIS mixers, which are essentially based on the design of the on-chip balanced SIS mixers at 490 GHz developed in our institute. Singleended HEB mixers are used for the laboratory tests of the optics. The LO power distribution is accommodated behind the FPU optics. It is composed of the LO optics, which includes a collimating Fourier grating, and an LO distribution plate to supply LO signal to each of the 9 pixels of the sub-array. Different options for the LO coupling design and fabrication are being analyzed and will be based on in-house hybrid waveguide/planar technology. We summarize the receiver project with emphasis on the cryogenics and the optics and present laboratory test results

13. Method of porous diamond deposition on porous silicon

NASA Astrophysics Data System (ADS)

Baranauskas, Vitor; Peterlevitz, Alfredo C.; Chang, Dahge C.; Durrant, Steven F.

2001-12-01

In this paper, we discuss the experimental results of the fabrication of porous diamond/porous silicon and porous diamond structures by chemical vapor deposition of diamond over a skeleton of porous silicon, replicating the porous surface geometry around the Si pores and also creating new porous diamond structures. Scanning electron microscopy (SEM) revealed that the diamond nuclei are deposited on the top of the porous silicon skeleton, forming isolated grains in the first nucleation stages, and then growing like the usual structure of most ceramic materials, making a self-sustained porous diamond structure. Raman spectroscopy revealed that the diamond films are of good quality, close to that of diamond films grown on crystalline silicon.

14. Voltage sensor and dielectric material

DOEpatents

Yakymyshyn, Christopher Paul; Yakymyshyn, Pamela Jane; Brubaker, Michael Allen

2006-10-17

A voltage sensor is described that consists of an arrangement of impedance elements. The sensor is optimized to provide an output ratio that is substantially immune to changes in voltage, temperature variations or aging. Also disclosed is a material with a large and stable dielectric constant. The dielectric constant can be tailored to vary with position or direction in the material.

15. Microwave Propagation in Dielectric Fluids.

ERIC Educational Resources Information Center

Lonc, W. P.

1980-01-01

Describes an undergraduate experiment designed to verify quantitatively the effect of a dielectric fluid's dielectric constant on the observed wavelength of microwave radiation propagating through the fluid. The fluid used is castor oil, and results agree with the expected behavior within 5 percent. (Author/CS)

16. Growth, defect structure, and THz application of stoichiometric lithium niobate

NASA Astrophysics Data System (ADS)

Lengyel, K.; Péter, Á.; Kovács, L.; Corradi, G.; Pálfalvi, L.; Hebling, J.; Unferdorben, M.; Dravecz, G.; Hajdara, I.; Szaller, Zs.; Polgár, K.

2015-12-01

holography and have the additional advantage to minimize the absorption even in the far-infrared (THz) range. The review also provides a discussion on the progress made in the characterization of non-stoichiometry related intrinsic and extrinsic defect structures in doped LN crystals, with emphasis on ODR-ion-doped and/or closely stoichiometric systems, based on both spectroscopic measurements and theoretical modelling, including the results of first principles quantum mechanical calculations on hydroxyl defects. It will also be shown that new perspective applications, e.g., the generation of high energy THz pulses with energies on the tens-of-mJ scale, are feasible with ODR-doped sLN crystals if optimal conditions, including the contact grating technique, are applied.

17. Short-length carbon nanotubes as building blocks for high dielectric constant materials in the terahertz range

NASA Astrophysics Data System (ADS)

Shuba, M. V.; Paddubskaya, A. G.; Kuzhir, P. P.; Maksimenko, S. A.; Flahaut, E.; Fierro, V.; Celzard, A.; Valusis, G.

2017-03-01

Due to the high polarizability of finite-length carbon nanotubes (CNTs) in the quasi-static regime, they can be considered as building blocks for the fabrication of high dielectric constant material. Our theoretical estimations, based on an effective medium approach and solutions of a boundary value problem for individual CNT, predict that composite materials comprising short-length CNTs can have very high dielectric constants (up to 300) and low dielectric loss tangents (below 0.03) in the terahertz range. In order to prove this, 500–1000 nm thick films comprising single- and multi-walled CNTs of both long (0.5–2 μm) and short (0.1–0.4 μm) lengths have been fabricated. The analysis, based on the time-domain terahertz spectroscopy in the range 0.2–1.0 THz, demonstrated a decrease in the dielectric loss tangents of the CNT-based materials with a reduction in CNT length. In the terahertz range, the films comprising short-length CNTs had a relative effective permittivity with a large real part (25–136) and dielectric loss tangent (0.35–0.60).

18. Terahertz dielectric response of ferroelectric Ba(x)Sr(1-x)TiO3 thin films.

PubMed

Kang, Seung Beom; Kwak, Min Hwan; Choi, Muhan; Kim, Sungil; Kim, Taeyong; Cha, Eun Jong; Kang, Kwang Yong

2011-11-01

Terahertz time-domain spectroscopy has been used to investigate the dielectric and optical properties of ferroelectric Ba(x)Sr(1-x)TiO(3) thin films for nominal x-values of 0.4, 0.6, and 0.8 in the frequency range of 0.3 to 2.5 THz. The ferroelectric thin films were deposited at approximately 700 nm thickness on [001] MgO substrate by pulsed laser deposition. The measured complex dielectric and optical constants were compared with the Cole-Cole relaxation model. The results show that the Cole-Cole relaxation model fits well with the data throughout the frequency range and the dielectric relaxation behavior of ferroelectric Ba(x)Sr(1-x)TiO(3) thin films varies with the films compositions. Among the compositions of Ba(x)Sr(1-x)TiO(3) films with different Ba/Sr ratios, Ba(0.6)Sr(0.4)TiO(3) has the highest dielectric constants and the shortest dielectric relaxation time.

19. Low dielectric polyimide fibers

NASA Technical Reports Server (NTRS)

Dorogy, William E., Jr. (Inventor); St.clair, Anne K. (Inventor)

1994-01-01

A high temperature resistant polyimide fiber that has a dielectric constant of less than 3 is presented. The fiber was prepared by first reacting 2,2-bis (4-(4aminophenoxy)phenyl) hexafluoropropane with 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride in an aprotic solvent to form a polyamic acid resin solution. The polyamic acid resin solution is then extruded into a coagulation medium to form polyamic acid fibers. The fibers are thermally cured to their polyimide form. Alternatively, 2,2-bis(4-(4-aminophenoxy)phenyl) hexafluoropropane is reacted with 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride to form a polyamic acid, and the polyamic acid is chemically converted to its polyimide form. The polyimide is then dissolved in a solvent to form a polyimide resin solution, and the polyimide resin is extruded into a coagulation medium to form a polyimide wet gel filament. In order to obtain polyimide fibers of increased tensile properties, the polyimide wet gel filaments are stretched at elevated temperatures. The tensile properties of the fibers were measured and found to be in the range of standard textile fibers. Polyimide fibers obtained by either method will have a dielectric constant similar to that of the corresponding polymer, viz., less than 3 at 10 GHz.

20. Folded dielectric elastomer actuators

NASA Astrophysics Data System (ADS)

Carpi, Federico; Salaris, Claudio; DeRossi, Danilo

2007-04-01

Polymer-based linear actuators with contractile ability are currently demanded for several types of applications. Within the class of dielectric elastomer actuators, two basic configurations are available today for such a purpose: the multi-layer stack and the helical structure. The first consists of several layers of elementary planar actuators stacked in series mechanically and parallel electrically. The second configuration relies on a couple of helical compliant electrodes alternated with a couple of helical dielectrics. The fabrication of both these configurations presents some specific drawbacks today, arising from the peculiarity of each structure. Accordingly, the availability of simpler solutions may boost the short-term use of contractile actuators in practical applications. For this purpose, a new configuration is here described. It consists of a monolithic structure made of an electroded sheet, which is folded up and compacted. The resulting device is functionally equivalent to a multi-layer stack with interdigitated electrodes. However, with respect to a stack the new configuration is advantageously not discontinuous and can be manufactured in one single phase, avoiding layer-by-layer multi-step procedures. The development and preliminary testing of prototype samples of this new actuator made of a silicone elastomer are presented here.
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