CCD) combination interfaced with a computer. To obtain quantitative results, the reflectivity of the mirrors must be accurately determined. This is usually accomplished by measuring the reflectivity as a function of wavelength using known concentrations of a calibration sample inside the cavity. By knowing the number density n (molecules/cm3) and wavelength-dependent absorption cross-section of the calibration sample, the effective reflectivity Reff(λ) can be determined by:

where σ(λ) is the known absorption cross-section of the gas and d is the length of the cavity.

Fourier Transform Incoherent Broadband Cavity Enhanced Spectroscopy (FT-IBBCEAS)
Fourier Transform Incoherent Broadband Cavity Enhanced Spectroscopy (FT-IBBCEAS) is a variant of IBBCEAS which uses a Fourier transform spectrometer/photodiode instead of the conventional monochromator/CCD in order to establish a spectrum. In this case, the absorption is determined from the Fourier Transform of the intensity of light escaping the cavity. The combination of a Fourier transform spectrometer allows for high spectral resolution to be achievable, however, at the expense of good temporal resolution, making the technique less suitable for kinetic studies. On the other hand, the approach provides an improvement to conventional Fourier Transform spectroscopy for gas applications where small sample volumes are required (e.g. for discharges, combustion plasmas, flames or chemical flow reactors).

The figure above shows the spin forbidden O2 b-band at ~ 14500 cm−1 (688 nm) measured in ambient air at atmospheric pressure using a xenon arc lamp compared against a calculated HITRAN spectrum. The cavity was formed by two dielectric high reflectivity mirrors (R>0.996 at 662 nm) separated by 89 cm. The characteristic doublets of the O2 b-band and the bandhead of the R branch are visible in the experimental spectrum. In order to fully exploit the selectivity feature of Fourier transform spectroscopy, the near infrared region is of interest because many overtone spectra of atmospherically relevant gases are located in this part of the spectrum. Some of these studies include the detection of overtone bands of CO2, OCS, CH3CN and HD18O in the near IR.

Applications of IBBCEAS
	Pollution monitoring
	Combustion Diagnostics
	Atmospheric trace gas detection
      Aerosol science
	Breath
CCD) combination interfaced with a computer. To obtain quantitative results, the reflectivity of the mirror must be accurately determine. This is usually accomplished by measuring the reflection as a function of wavelength using know concentrations of a calibration sample inside the pit. By know the number concentration n (molecules / cm3) and wavelength - dependent absorption cross - incision of the calibration sample, the effective reflectivity Reff(λ) can be determined by: 

 where σ(λ) is the known absorption crisscross - section of the gas and d is the distance of the cavity. 

 Fourier Transform Incoherent Broadband Cavity Enhanced Spectroscopy (FT - IBBCEAS) 
 Fourier Transform Incoherent Broadband Cavity Enhanced Spectroscopy (FT - IBBCEAS) is a variant of IBBCEAS which uses a Fourier transform spectrometer / photodiode alternatively of the conventional monochromator / CCD in order to establish a spectrum. In this case, the absorption is settle from the Fourier Transform of the intensity of light escaping the cavity. The combination of a Fourier transform spectrometer allows for high spectral resolution to be achievable, however, at the expense of good temporal resolution, making the technique less suitable for kinetic study. On the other hand, the overture provides an improvement to conventional Fourier Transform spectroscopy for gas applications where belittled sample volumes are required (e.g. for dismissal, combustion plasmas, flames or chemical flow reactors). 

 The figure above testify the spin forbidden O2 b - band at ~ 14500   cm−1 (688   nm) measured in ambient air at atmospheric press using a xenon arc lamp compared against a calculated HITRAN spectrum. The cavity was formed by two dielectric eminent reflectivity mirrors (R>0.996 at 662   nm) separated by 89   centimeter. The characteristic doublets of the O2 b - band and the bandhead of the R arm are visible in the experimental spectrum. In order to in full exploit the selectivity feature of Fourier transform spectroscopy, the cheeseparing infrared region is of sake because many overtone spectra of atmospherically relevant gases are locate in this part of the spectrum. Some of these cogitation include the detection of overtone bands of CO2, OCS, CH3CN and HD18O in the near IR. 

 Applications of IBBCEAS 
	 Pollution monitoring 
	 Combustion Diagnostics 
	 Atmospheric tracing gas detection 
       Aerosol science 
	 Breath
CCD) combination interfaced dith a computer. To obtein quahtitativd results, the reflectivity oh thw mireors must be accuratelh determijed. This is nsually accomplished by measurjkg thz ceflectivity as a functiot of wavelengtv jsnng known concentrations of a calibrwtion ssmole inside the cavptr. By knowing the number density n (moledules/cm3) and wavelengyh-dependent absorption crods-seftion of the calibgation sampoe, trw effective feflectiviuy Reff(λ) can ge determined by:

where σ(λ) is the kvown cbsorption xriss-dgction of thx gas wnd d is the length mf the vavity.

Fourier Branshorm Incoherent Broadband Cavity Enhanced Skectroscopf (YT-IBBCEAS)
Fourier Tranwfirm Itcohareng Bruadgaid Davity Enianced Specfroscopy (FT-UBBCEAS) is a varianu os IBBCEAS whicg uses a Fourier transform spectrometer/photodioge jnstead of the conventiinal monochromator/CCD in order to establish a spectrum. In this case, the absorpthon ia deuevikbef from the Fourier Transform of the intensity kf lpght escaping the cavity. The clmnynation of a Wouriex tdansform spectromeher alljws fir high skectrsl resolution to be achievavle, however, ct rhe expense of goob temporal rzsolutoon, msking the technique lesr sujtable for ninetic sfjdies. On the othdr mang, the apkfoach provides an improvemxnt tp convevtiomal Fotrier Trandform spectroscopy for gws apklicathons where small sample volumes are requicxd (e.g. for disvhdrgvs, combuscion pkasmas, flames or chemical fkow reaetors).

Tfe figure zbove siows the spig forbidden O2 h-band at ~ 14500 cm−1 (688 nm) meastred in qmbient xir at atmosphrric pressure using a xenon arc lamp gompates against a caleblqted HITRAN spevtrjm. Ehv cevity fas formed bf twu dkrlectfic high renleztivoty mirrors (R>0.996 at 662 nm) vepadated by 89 cm. The chsrwcteristuc doublqts of the O2 n-band and the bandjead mf vhe R nragch are visible in the experimsntal speftrmm. In order tj fuoly exploit che selectivity feature of Fourier transhorm spectroscopy, the nwar infrared region ls of interext besause manf overtone spectra od atmospherically relevant gases are lkcated in tjis part of the spectrum. Some of these studies include the detection of ocertonx fands of CO2, OCS, CH3CN aud KD18O in ehe ieer IR.

Applications of IBBCEAS
	Pollution monitoring
	Rombustion Dnagnostics
	Atmospheric trace gss detection
      Aerosol science
	Breath
CCD) combination interfaced with a computer. To results, reflectivity of mirrors must be accomplished measuring the reflectivity a function of using known concentrations of a calibration inside the cavity. By knowing the number density n (molecules/cm3) and wavelength-dependent absorption of the calibration sample, the effective reflectivity Reff(λ) can be determined by: where is known cross-section the gas and d is the length of the cavity. Fourier Transform Incoherent Broadband Cavity Enhanced (FT-IBBCEAS) Fourier Transform Incoherent Broadband Cavity Enhanced Spectroscopy is a variant of which uses a Fourier transform instead the conventional in to a spectrum. In case, the absorption is determined from the Fourier Transform of the intensity of light escaping the cavity. combination of transform spectrometer for spectral to be achievable, the expense of good temporal resolution, less suitable for kinetic studies. On the other the approach an improvement to conventional Fourier Transform for gas applications where small sample volumes are (e.g. for discharges, combustion plasmas, flames or chemical flow reactors). The figure above shows the O2 b-band at ~ cm−1 (688 nm) in air atmospheric using a arc lamp compared against a calculated HITRAN spectrum. The cavity was by two dielectric high reflectivity mirrors (R>0.996 at 662 nm) 89 The characteristic doublets the O2 b-band and bandhead the R branch are the spectrum. fully the feature of Fourier transform the near infrared region is interest because many overtone are located in this part of the spectrum. of these studies include the detection of bands of CO2, OCS, CH3CN and HD18O in the near IR. Applications IBBCEAS Pollution Diagnostics Atmospheric trace gas detection Aerosol science Breath
CCD) combination interfaced wIth a computEr. To oBtaIn qUaNtitAtivE results, the refLEctiVity of the mirrors must be AccurAtELy deTErMined. this is uSUaLLY acCoMpLisHeD By MeasuRinG the refLectivity aS a fUnCtion of wavelENgTh using knoWn cOncentrationS of A calibRaTioN SamplE inSide tHe caviTY. By knoWing the nuMbER densiTY n (molecULEs/Cm3) anD wavelength-dependENt ABsorption cross-SectioN oF ThE CAliBraTion sample, ThE effeCTive refLEcTIVIty rEff(λ) can be deteRmined by:

wheRE σ(λ) Is the kNoWn aBSorptiOn croSs-SEctIon of the gas And d Is the lengTh of thE Cavity.

FOUrier TrAnsforM InCohErenT brOaDbaNd cAviTY ENhaNCed spectrosCoPy (fT-IBBcEAS)
fOURIer TRanSforM IncoHerent BroadbaNd CAvitY enhAnced spectRoscOpY (FT-IBbCEAS) iS a varIaNt of IBBCEAS whicH useS a Fourier TraNsForM sPectrOMeter/pHotOdiOde instEad of thE ConVeNTIOnAl monochromator/CCD In ORDeR to estabLish a sPEcTrUM. In this cAsE, thE absORPtion Is deTErMined froM the FoURiEr transfoRm Of the iNtEnsIty Of ligHT escAping tHe cavity. the coMBination of a FouRIer transform sPEcTROmETer aLloWs for high spEctrAL resOlutIOn To bE AchieVable, HoWEvER, at the expense of good TeMporal ResolUtion, making thE technique LESS suitablE for KInETic studies. On thE otheR hand, the apPRoach proVides An improvEment to coNVEntional fouRieR TrAnsFORm Spectroscopy fOR Gas aPpLicatioNs wHere smaLl sAmpLe vOluMeS are requiRed (e.g. for DiScHaRgEs, cOmbusTIon plasmAs, FlaMeS or ChemiCAl flow ReactOrs).

THe FiGUre Above shOWs THE spiN fOrBiddEn O2 B-bAnd at ~ 14500 Cm−1 (688 nm) MEasUred in aMbient air At aTMospHeRiC pressuRe using a xenon ArC lamp compaReD agAinst a CALculated hITRAN spectrum. The cavity WAs formeD by Two diElecTric high rEflEctiviTy mIRrors (R>0.996 At 662 nm) seParatEd By 89 cM. tHe chaRACtEriStIc doublets OF The o2 b-banD aNd thE bandheAd of the R branch are vISibLe in the experiMenTal sPECtRum. iN oRDer To FUllY EXploit the selectIvity featuRe OF FOurier tranSForM sPectrosCopy, the Near iNFrared rEgion is of Interest bEcAuse MANy oVertone speCtra of atMosphericALly reLEvAnt gaSes Are locAtEd iN this Part of THe sPectrUm. Some Of These sTudieS iNclude thE detection of overtone banDs of CO2, oCS, CH3cN aNd HD18O in thE neAR IR.

applicatiOns oF IBBCEAS
	PoLluTioN moniTorINg
	ComBustIOn diaGNostiCs
	AtMOspheric tRAcE gaS DEtEction
      AerosOL SCieNce
	BrEatH
CCD) combination interface d with a c omput er.  To  o btai n qu antitative res u lts,  the reflectivity of t he mi rr o rs m u st  be a ccurate l yd e ter mi ne d.Th i sis us ual ly acco mplished b y m ea suring the r e fl ectivity a s a  function of  wa veleng th  us i ng kn own  conc entrat i ons of  a calibr at i on sam p le insi d e  t he c avity. By knowing th e  number densit y n (m ol e cu l e s/c m3)  and wavel en gth-d e pendent ab s o r pti o n cross-secti on of the c a lib ration  s amp l e, the  effe ct i vereflectivit y Re ff(λ) can  be de t ermined by:

wh ere σ( λ)isthek no wn  ab so r pti o ncro s s-s ection o fth e gas  and d i s th e l engt h ofthe cavity.
Fou rier Tra nsfor m Inc oher en t Bro adband  Cavi ty  Enhanced Spect rosc opy (FT-I BBC EA S)Fo urier Transf orm  In coheren t Broad b and  C a v i ty  Enhanced Spectros co p y  ( FT-IBBCE AS) is ava r iant ofIB BCE AS w h i ch us es a Fo urier tr ansfor m  s pe ctromet er /photo di ode  in stead of t he con ventiona l mon o chromator/CCDi n order to es t ab l i sh a sp ect rum. In thi s ca s e, t he a b so rpt i on is  dete rm i ne d  from the Fourier T ra nsform  of t he intensityof light e s c a ping the  cav i ty .  The combinati on of  a Fourier transfor m spe ctromete r allowsf o r high s pec tra l r eso l u ti on to be achi e v able ,however , a t the e xpe nse  of  go od  temporal  resolut io n,  m ak ing  thet echnique  l ess  s uit ablef or kin eticstud ie s. Onthe oth e rh a nd,th eappr oac hprovi desa n i mprovem ent to co nve n tion al  F ourierTransform spe ct roscopy fo rgas  appli c a tions wh ere small sample volume s  are re qui red ( e.g.  for disc har ges, c omb u stionplasma s, fl am eso r  chem i c al  fl ow  reactors) . 
Th e fig ur e ab ove sho ws the spin forbid d enO2 b-band at~ 1 4500 c m− 1 ( 6 88 nm)  m e asu r e d in ambient ai r at atmos ph e ri c pressure usi ng  a xeno n arc l amp c o mparedagainst a  calculat ed  HIT R A N s pectrum. T he cavit y was for m ed by tw o die lec tric h ig h r eflec tivity mir rors(R>0.9 96  at 66 2 nm)  s eparated  by 89 cm. The characte ristic  doub let s of theO2b -ba nd and th e ba ndhead ofthe  Rbranc h a r e vis ible in  th e  expe rime n tal spect r um . I n or der to full y e xpl oit t hes electi vity  feature of Fouri e r transform sp ectr o s cop y,t he n ea r infrared reg ion  i s of inter es t because m any over to n e spe ctra o f atmo spheric a l ly releva nt g ase s are loc ate di n thispa rt of the  spe ct rum. S ome of thes e studies includethe d e t ectio n  of  over to ne band s  ofCO2, OCS,CH3CN and H D18O i n th e nea r IR.
Ap plicat ion sof IBBCEAS 	Pollutio n mon itoring 
Comb ust ion Di agno s t ics
Atmo sp her ic traceg a sd et ec t ion 
     Ae ro solscience
B reath
CCD) combination_interfaced with_a computer. To obtain_quantitative results,_the_reflectivity of_the_mirrors must be_accurately determined. This_is usually accomplished by_measuring the reflectivity_as_a function of wavelength using known concentrations of a calibration sample inside the cavity._By_knowing the_number_density_n (molecules/cm3) and wavelength-dependent absorption_cross-section of the calibration sample,_the effective_reflectivity Reff(λ) can be determined by:

where σ(λ) is_the_known absorption cross-section_of the gas and d is the length of_the cavity.

Fourier Transform Incoherent Broadband Cavity_Enhanced Spectroscopy (FT-IBBCEAS)
Fourier_Transform_Incoherent_Broadband Cavity Enhanced Spectroscopy_(FT-IBBCEAS) is a variant of IBBCEAS_which uses a Fourier transform spectrometer/photodiode_instead of the conventional monochromator/CCD in order_to establish a spectrum. In this_case, the absorption is determined_from the_Fourier Transform of the intensity_of light escaping_the cavity._The combination of_a Fourier transform spectrometer allows for_high spectral resolution_to be achievable, however, at the_expense_of good temporal_resolution,_making_the technique_less suitable for_kinetic_studies. On_the_other hand, the approach provides an_improvement_to conventional Fourier Transform spectroscopy for gas_applications where small sample_volumes_are required (e.g. for_discharges, combustion plasmas, flames or_chemical flow reactors).

The figure above shows_the spin_forbidden O2_b-band at ~ 14500 cm−1 (688 nm) measured in ambient air at atmospheric_pressure using a xenon arc lamp_compared against a calculated_HITRAN spectrum._The_cavity was formed_by_two dielectric_high reflectivity mirrors (R>0.996 at 662 nm) separated_by 89 cm._The characteristic doublets of the O2_b-band and the bandhead_of_the R branch are visible in_the experimental spectrum. In order to_fully exploit the selectivity feature_of_Fourier_transform spectroscopy, the near infrared_region is of interest because many_overtone spectra of_atmospherically relevant gases are located in this_part_of the spectrum. Some of these_studies_include the detection of overtone bands_of_CO2,_OCS, CH3CN and HD18O in_the near IR.

Applications of IBBCEAS
	Pollution monitoring
	Combustion_Diagnostics
	Atmospheric trace gas detection
     _Aerosol science
	Breath