Etude et réalisation de dispositifs optiques à large couverture spectrale pour la détection multi-gaz à distance

Abstract : The aim of this work is to study and validate new active methods based on infrared absorption spectroscopy for remote detection of multiple-gas species. For this application, we studied the potentiality of two innovative laser sources : a Doubly Resonant Optical Parametric Oscillator (DROPO) and a fiber Supercontinuum laser, emitting either a monochromatic radiation, tunable in the 3.3-3.7µm range or a continuous spectrum from 1µm to beyond 3.8µm, respectively. In order to determine the precision of concentration measurements, the Cramer-Rao Bounds (CRB) have been computed after modelling the signal and the noise for both sources. Next, multiple-gas species concentration estimators, adapted to the DROPO and Supercontinuum signals, have been developed. These estimators were applied to experimental data in order to validate the calculation of the performance prediction. In the case of DROPO spectroscopy, the mean concentrations of atmospheric water vapour and methane have been demonstrated over a 30m range (using backscattering onto a non-cooperative target). In the case of Supercontinuum spectroscopy, a near infrared source and a commercial grating optical spectrometer have been used to validate the signal processing and the predicted precision. Simultaneous measurements of methane quantity in a gas cell and atmospheric water vapour concentration have been performed over a 10m range (after reflection onto a cooperative target). The estimations are unbiased and their standard deviations remain lower than 1.5 times the CRB. For infrared spectroscopy around 3.3µm, a spectrograph was adapted, mounted and calibrated. This instrument is able to acquire in a few seconds 100 spectra, over a 200nm spectral range, with a resolution below 1nm. A maximum likelihood estimator retrieves little biaised estimations (below 3%) and a standard deviation equal to 2.5 times the BCR. We thus have experimentally demonstrated the feasibility of fast and precise infrared Supercontinuum spectroscopy measurements.
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Contributor : Alexandre Dobroc <>
Submitted on : Sunday, March 16, 2014 - 11:19:13 AM
Last modification on : Tuesday, March 26, 2019 - 2:24:02 PM
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Alexandre Dobroc. Etude et réalisation de dispositifs optiques à large couverture spectrale pour la détection multi-gaz à distance. Optique [physics.optics]. Ecole Polytechnique X, 2013. Français. ⟨pastel-00959752⟩

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