Multi-gas sensing based on photoacoustic spectroscopy using tunable laser diodes

Multi-hydrogenated compounds detection based on photoacoustic (PA) spectroscopy is reported. Three near-infrared semiconductor lasers are used with a resonant PA cell operated in its first longitudinal mode to monitor methane, water vapour and hydrogen chloride in the parts per million range. The design of our cell results from simulations performed in order to optimise its performances. Influence of the buffer gas on the PA signal has also been analysed, both theoretically and experimentally. A reduction of the PA signal of almost one order of magnitude has been observed between N-2 and He, which demonstrates the importance of the buffer gas in PA spectroscopy. Finally, detection limits of 0.5 ppm Of CH4 and 3 ppm of HCl has been achieved experimentally in nitrogen and an H2O sensitivity of 0.2 ppm has been estimated. (C) 2004 Elsevier B.V. All rights reserved.