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Proceedings Paper

Measurement of trace gases by diode laser cavity ringdown spectroscopy
Author(s): Daniele Romanini; Alexander A. Kachanov; Jerome Morville; Marc Chenevier
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Paper Abstract

Optical spectroscopic methods based on direct absorption offer a quantitative measurement of the absorbance, which is the product of the concentration, the molar absorption coefficient of the transition being observed and the length of the absorption path. An absorption sensitivity adequate for trace detection may be achieved by increasing the path length. One solution is offered by cavity ringdown spectroscopy (CRDS), attractive for its simplicity. We recently demonstrated that an external cavity diode laser (ECDL) can be conveniently employed for CRDS instead of a pulsed laser, contrary to previous applications. Here we extend this result to distributed feed-back (DFB) diode lasers. Paying special attention to the coupling of the laser source to the cavity, we developed an extremely simplified CRDS scheme with a sensitivity of about 10-8/cm/(root)Hz. We then built detectors for methane and HF, working close to the optical wavelengths 1.65 and 1.31 micrometer, respectively With an optical assembly of about 50 cm length and a response time of about 1 s, these devices accurately measure atmospheric methane concentrations in the range 0.5 to 200 ppmv, and HF concentrations from 0.1 to 50 ppmv.

Paper Details

Date Published: 16 September 1999
PDF: 11 pages
Proc. SPIE 3821, Environmental Sensing and Applications, (16 September 1999); doi: 10.1117/12.364170
Show Author Affiliations
Daniele Romanini, Lab. de Spectrometrie Physique (France) and Univ. Joseph Fourier (France)
Alexander A. Kachanov, Lab. de Spectrometrie Physique (France) and Univ. Joseph Fourier (France)
Jerome Morville, Lab. de Spectrometrie Physique (France) and Univ. Joseph Fourier (France)
Marc Chenevier, Lab. de Spectrometrie Physique (France) and Univ. Joseph Fourier (France)


Published in SPIE Proceedings Vol. 3821:
Environmental Sensing and Applications

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