Miniature single-fiber photoacoustic sensor for methane gas leakage detection

A miniature single-fiber photoacoustic (PA) sensor was designed and proposed for the detection of trace amount of methane gas. A Fabry-Perot (FP) interferometric cantilever was used to monitor the PA signal generated by the methane gas having absorbed the laser energy. Therefore, a pump laser and a probe light source were required in this system and coupled by a wavelength division multiplexer (WDM) to transmit in only one fiber. A communal cavity utilized both as the FP cavity and the PA cell was designed and optimized. The principles behind the determination of the cell size were explored. The single-fiber and the communal cavity contributed to the small volume of the cell, which was calculated to be only similar to 1.7 mu L. Experiments were designed to verify the practicability of the PA sensor. Operating at the resonant frequency of 1648 Hz, the real-time response time was measured to be similar to 23 s. The minimum detectable limit (MDL) was 8.4 ppm with a 1 s lock-in integral time.