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Photoacoustic Resonant Cell Remodified from Helmholtz Cavity for Multi-Gas Sensing Using Infrared Lasers

This paper presents method and performance of the photoacoustic resonant cell remodified from Helmholtz cavity that can be used to detect photoacoustic signal of multi-gas. This technique has its physical basis in a phenomenon called the photoacoustic effect. The experiment system is composed of a resonant Helmholtz cavity, a sensitive microphone and two infrared lasers with high adsorption capability and specificity to the analyte. In our experiments, the average optical power at the laser operating point is 200mW for the 972nm laser (H2O detection) and 800mW for the10.653um laser (CO2 detection), which are modulated at two different frequencies f1=175Hz and f2=125Hz. The remodified Helmholtz resonant on-line and real time measurement of the water vapour (300ppm) and carbodioxide (300ppm) conducted at their respective resonant frequency shown large signals about 4.41mV and 19.77mV respectively. The result demonstrated this cell used to test multi-gas is also feasible.