Photoacoustic spectroscopy based multi-gas detection using high-sensitivity fiber-optic low-frequency acoustic sensor

We demonstrate a high-sensitivity fiber-optic low-frequency acoustic sensor based on a thin Parylene-C diaphragm. The excellent diaphragm forming ability and good adhesion of Parylene-C make the sensor fabricate up to 9 mm in diameter. For the acoustic pressure of 50 mPa at the frequency of 30 Hz, acoustic testing demonstrates a signal to noise ratio of 37 dB, which is almost seven times higher than a conventional electric microphone. The low-frequency acoustic sensor, together with an infrared thermal radiation source, and a non-resonant cell, constitutes a photoacoustic detection system for multiple trace gases analysis. The detection limits of acetylene (C2H2), methane (CH4), ethane (C2H6), ethylene (C2H4), carbon monoxide (CO) and carbon dioxide (CO2) are achieved to be 0.11, 0.21, 0.13, 0.16, 0.15 and 0.48 parts-per-million, respectively. The detection system is applied to detect mixture of the six gases, and the average deviations of the six gases are not more than 5.0%.