Reference EPFL-CONF-163061 URL: http://tdls.conncoll.edu/2005/index.html Record created on 2011-02-04, modified on 2017-05-10

Novel Helmholtz-based photoacoustic sensor for trace gas detection at ppm level using GaInAsSb/GaAlAsSb DFB lasers

First investigations of photoacoustic (PA) spectroscopy (PAS) of methane using an antimonide semiconductor laser are reported. The laser fabrication is made in two steps. The structure is firstly grown by molecular beam epitaxy, then a metallic distributed-feedback (DFB) grating is processed. The laser operates at 2371.6 nm in continuous wave and at room temperature. It demonstrates single-mode emission with typical tuning coefficients of 0.04 nm mA(-1) and 0.2 nm K(-1). PA detection of methane was performed by coupling this laser into a radial PA cell. A detection limit of 20 ppm has been achieved in a preliminary configuration that was not optimised for the laser characteristics.

Application of antimonide diode lasers in photoacoustic spectroscopy

Type I antimonide diode lasers operate in the 2000 to 2800 nm spectral region. Compared to the 1300 to 1650nm communications spectral band, the antimonide band can access stronger molecular transitions and thus potentially achieve higher sensitivity. Compared to quantum cascade or lead-salt lasers operating at longer infrared wavelengths,antimonide lasers have the advantage that both laser and detector technology support room temperature, cw operation. This paper describes experiments to measure ammonia and methane simultaneously, with high sensitivity and fast response, using a distributed feedback laser at 2200 nm. Our approach is based on scanning the laser over a small spectral regionthat encompasses several lines, either by varying the laser temperature or current, while simultaneously using wavelength modulation with harmonic detection to record the spectrum. Temperature scanning is slower but can cover a wider spectral interval. Digital signal processing methods, including classical least squares and singular value decomposition, extract the gas concentrations from the measured spectra. The accuracy and precision of these algorithms are compared in two limits: the limit when both gases are absent or present only at low levels, and the limit when the concentration of one gas is high.

Detecting ammonia and methane with antimonide lasers

Both pseudo-random amplitude modulation and pseudo-random tone-burst modulation methods were applied to determine range resolved cavity losses in a cylindrical-mirror cavity excited by a distributed feedback laser. Gas concentrations were determined.

David S. Bomse

Papers

Detecting ammonia and methane with antimonide lasers

Pseudo-Random Modulation Methods for Cavity-Enhanced Spectroscopy