Trace gas measurements using optically resonant cavities and quantum cascade lasers operating at room temperature

S. Welzel, G. Lombardi, P.B. Davies, R.A.H. Engeln, D.C. Schram, J. Röpcke

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Achieving the high sensitivity necessary for trace gas detection in the midinfrared mol. fingerprint region generally requires long absorption path lengths. In addn., for wider application, esp. for field measurements, compact and cryogen free spectrometers are definitely preferable. An alternative approach to conventional linear absorption spectroscopy employing multiple pass cells for achieving high sensitivity is to combine a high finesse cavity with thermoelec. (TE) cooled quantum cascade lasers (QCLs) and detectors. We have investigated the sensitivity limits of an entirely TE cooled system equipped with an .apprx.0.5 m long cavity having a small sample vol. of 0.3 l. With this spectrometer cavity enhanced absorption spectroscopy employing a continuous wave QCL emitting at 7.66 micro m yielded path lengths of 1080 m and a noise equiv. absorption of 2 * 10-7 cm-1 Hz-1/2. The mol. concn. detection limit with a 20 s integration time was found to be 6*108 mols./cm3 for N2O and 2 * 109 mols./cm3 for CH4, which is good enough for the selective measurement of trace atm. constituents at 2.2 mbar. The main limiting factor for achieving even higher sensitivity, such as that found for larger vol. multi pass cell spectrometers, is the residual mode noise of the cavity. On the other hand the application of TE cooled pulsed QCLs for integrated cavity output spectroscopy and cavity ring-down spectroscopy (CRDS) was found to be limited by the intrinsic frequency chirp of the laser. Consequently the accuracy and advantage of an abs. internal absorption calibration, in theory inherent for CRDS expts., are not achievable.
Originele taal-2Engels
Artikelnummer093115
Pagina's (van-tot)093115-1/15
TijdschriftJournal of Applied Physics
Volume104
Nummer van het tijdschrift9
DOI's
StatusGepubliceerd - 2008

Vingerafdruk

quantum cascade lasers
cavity resonators
cavities
room temperature
gases
sensitivity
spectrometers
absorption spectroscopy
spectroscopy
rings
continuous wave lasers
chirp
cells
pulsed lasers
output
detectors
lasers

Citeer dit

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title = "Trace gas measurements using optically resonant cavities and quantum cascade lasers operating at room temperature",
abstract = "Achieving the high sensitivity necessary for trace gas detection in the midinfrared mol. fingerprint region generally requires long absorption path lengths. In addn., for wider application, esp. for field measurements, compact and cryogen free spectrometers are definitely preferable. An alternative approach to conventional linear absorption spectroscopy employing multiple pass cells for achieving high sensitivity is to combine a high finesse cavity with thermoelec. (TE) cooled quantum cascade lasers (QCLs) and detectors. We have investigated the sensitivity limits of an entirely TE cooled system equipped with an .apprx.0.5 m long cavity having a small sample vol. of 0.3 l. With this spectrometer cavity enhanced absorption spectroscopy employing a continuous wave QCL emitting at 7.66 micro m yielded path lengths of 1080 m and a noise equiv. absorption of 2 * 10-7 cm-1 Hz-1/2. The mol. concn. detection limit with a 20 s integration time was found to be 6*108 mols./cm3 for N2O and 2 * 109 mols./cm3 for CH4, which is good enough for the selective measurement of trace atm. constituents at 2.2 mbar. The main limiting factor for achieving even higher sensitivity, such as that found for larger vol. multi pass cell spectrometers, is the residual mode noise of the cavity. On the other hand the application of TE cooled pulsed QCLs for integrated cavity output spectroscopy and cavity ring-down spectroscopy (CRDS) was found to be limited by the intrinsic frequency chirp of the laser. Consequently the accuracy and advantage of an abs. internal absorption calibration, in theory inherent for CRDS expts., are not achievable.",
author = "S. Welzel and G. Lombardi and P.B. Davies and R.A.H. Engeln and D.C. Schram and J. R{\"o}pcke",
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Trace gas measurements using optically resonant cavities and quantum cascade lasers operating at room temperature. / Welzel, S.; Lombardi, G.; Davies, P.B.; Engeln, R.A.H.; Schram, D.C.; Röpcke, J.

In: Journal of Applied Physics, Vol. 104, Nr. 9, 093115, 2008, blz. 093115-1/15.

Onderzoeksoutput: Bijdrage aan tijdschriftTijdschriftartikelAcademicpeer review

TY - JOUR

T1 - Trace gas measurements using optically resonant cavities and quantum cascade lasers operating at room temperature

AU - Welzel, S.

AU - Lombardi, G.

AU - Davies, P.B.

AU - Engeln, R.A.H.

AU - Schram, D.C.

AU - Röpcke, J.

PY - 2008

Y1 - 2008

N2 - Achieving the high sensitivity necessary for trace gas detection in the midinfrared mol. fingerprint region generally requires long absorption path lengths. In addn., for wider application, esp. for field measurements, compact and cryogen free spectrometers are definitely preferable. An alternative approach to conventional linear absorption spectroscopy employing multiple pass cells for achieving high sensitivity is to combine a high finesse cavity with thermoelec. (TE) cooled quantum cascade lasers (QCLs) and detectors. We have investigated the sensitivity limits of an entirely TE cooled system equipped with an .apprx.0.5 m long cavity having a small sample vol. of 0.3 l. With this spectrometer cavity enhanced absorption spectroscopy employing a continuous wave QCL emitting at 7.66 micro m yielded path lengths of 1080 m and a noise equiv. absorption of 2 * 10-7 cm-1 Hz-1/2. The mol. concn. detection limit with a 20 s integration time was found to be 6*108 mols./cm3 for N2O and 2 * 109 mols./cm3 for CH4, which is good enough for the selective measurement of trace atm. constituents at 2.2 mbar. The main limiting factor for achieving even higher sensitivity, such as that found for larger vol. multi pass cell spectrometers, is the residual mode noise of the cavity. On the other hand the application of TE cooled pulsed QCLs for integrated cavity output spectroscopy and cavity ring-down spectroscopy (CRDS) was found to be limited by the intrinsic frequency chirp of the laser. Consequently the accuracy and advantage of an abs. internal absorption calibration, in theory inherent for CRDS expts., are not achievable.

AB - Achieving the high sensitivity necessary for trace gas detection in the midinfrared mol. fingerprint region generally requires long absorption path lengths. In addn., for wider application, esp. for field measurements, compact and cryogen free spectrometers are definitely preferable. An alternative approach to conventional linear absorption spectroscopy employing multiple pass cells for achieving high sensitivity is to combine a high finesse cavity with thermoelec. (TE) cooled quantum cascade lasers (QCLs) and detectors. We have investigated the sensitivity limits of an entirely TE cooled system equipped with an .apprx.0.5 m long cavity having a small sample vol. of 0.3 l. With this spectrometer cavity enhanced absorption spectroscopy employing a continuous wave QCL emitting at 7.66 micro m yielded path lengths of 1080 m and a noise equiv. absorption of 2 * 10-7 cm-1 Hz-1/2. The mol. concn. detection limit with a 20 s integration time was found to be 6*108 mols./cm3 for N2O and 2 * 109 mols./cm3 for CH4, which is good enough for the selective measurement of trace atm. constituents at 2.2 mbar. The main limiting factor for achieving even higher sensitivity, such as that found for larger vol. multi pass cell spectrometers, is the residual mode noise of the cavity. On the other hand the application of TE cooled pulsed QCLs for integrated cavity output spectroscopy and cavity ring-down spectroscopy (CRDS) was found to be limited by the intrinsic frequency chirp of the laser. Consequently the accuracy and advantage of an abs. internal absorption calibration, in theory inherent for CRDS expts., are not achievable.

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DO - 10.1063/1.3008014

M3 - Article

VL - 104

SP - 093115-1/15

JO - Journal of Applied Physics

JF - Journal of Applied Physics

SN - 0021-8979

IS - 9

M1 - 093115

ER -