Molecular dispersion spectroscopy for chemical sensing using chirped mid-infrared quantum cascade laser

A spectroscopic method of molecular detection based on dispersion measurements using a frequency-chirped laser source is presented. An infrared quantum cascade laser emitting around 1912 cm(-1) is used as a tunable spectroscopic source to measure dispersion that occurs in the vicinity of molecular r...

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Bibliographic Details
Published in:Optics express 2010-12, Vol.18 (25), p.26123-26140
Main Authors: Wysocki, Gerard, Weidmann, Damien
Format: Article
Language:English
Subjects:
Equipment Design
Equipment Failure Analysis
Lasers
Nitrogen - analysis
Quantum Theory
Spectrophotometry, Infrared - instrumentation
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Summary:A spectroscopic method of molecular detection based on dispersion measurements using a frequency-chirped laser source is presented. An infrared quantum cascade laser emitting around 1912 cm(-1) is used as a tunable spectroscopic source to measure dispersion that occurs in the vicinity of molecular ro-vibrational transitions. The sample under study is a mixture of nitric oxide in dry nitrogen. Two experimental configurations based on a coherent detection scheme are investigated and discussed. The theoretical models, which describe the observed spectral signals, are developed and verified experimentally. The method is particularly relevant to optical sensing based on mid-infrared quantum cascade lasers as the high chirp rates available with those sources can significantly enhance the magnitude of the measured dispersion signals. The method relies on heterodyne beatnote frequency measurements and shows high immunity to variations in the optical power received by the photodetector.
ISSN:1094-4087
1094-4087
DOI:10.1364/OE.18.026123