## Master's Theses

Summer 2012

#### Degree Type

Thesis - Campus Access Only

#### Degree Name

Master of Science (MS)

#### Department

Physics and Astronomy

Peter Beyersdorf

#### Keywords

fiber laser, frequency comb, potassium, rubidium, two photon spectroscopy

Physics

#### Abstract

Alkali atoms, such as rubidium and cesium, have been well studied because their atomic structures are relatively easy to calculate. The main purpose of this research was to observe the hyperfine structure of the 5D state of ⁸⁵ Rb and ⁸⁷ Rb via direct frequency comb spectroscopy (DFCS). Rubidium's well-understood atomic structure was a great tool in exploring the working mechanism of the frequency comb and its application to spectroscopy. Once the DFCS technique is validated, it will hold the potential to enable a wide variety of ultra-precise spectroscopy of atoms such as potassium or samarium in order to look for new and exotic physics, such as the permanent electric dipole moment of electrons, the asymmetry between matter and anti-matter in the universe, and variation of the fine structure constant.

\indent The frequency comb is a series of evenly spaced frequency modes which is generated by a erbium-doped fiber laser. The comb, mode spacing at ≈ 250 MHz, was used to probe two atomic transitions in rubidium, 5S½→ 5P and 5P → 5D. The atomic population of the final 5D state was monitored via fluorescence from the second stage of a cascade decay. The spectrum of the fluorescence intensity reflected the hyperfine structure of the 5D state. The spectrum was compared to a theoretical model and to another spectrum which was generated by a different frequency comb whose mode spacing was ≈ 925 MHz. From this comparison, we discovered how the fluorescence spectra depended on the mode spacing and the energy differences among various atomic levels.

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