Photoacoustic trace gas detection of ethylene in high-concentration methane background based on dual light sources and fiber-optic microphone

•An all-optical PA system based on dual light sources and a FOM.•Trace gas detection of ethylene in high-concentration methane background.•A lock-in WLI based demodulator was developed for detection of 1f and 2f PA signal.•The detection limit of ethylene reached 200 ppb over a range of 0–100% methane concentration background. An all-optical photoacoustic (PA) system for trace gas detection of ethylene (C2H4) in high-concentration methane (CH4) background has been developed based on dual light sources and fiber-optic microphone (FOM). C2H4 was measured by an infrared thermal radiation emitter. To eliminate the interference of high-concentration CH4 gas, a near-infrared laser source is used to measure the concentration of CH4 for self-correction. Light from the two sources was incident from both ends of the non-resonant PA cell, respectively. The concentration of the two gases was measured by time division multiplexing. The generated PA pressure signal was detected by a fiber-optic Fabry-Perot microphone, which was demodulated by a high-speed spectrometer. A lock-in white-light interferometry (WLI) based demodulator was developed for ultra-high sensitivity detection of 1f and 2f PA signal. Experimental results showed that the detection limit of C2H4 reached 200 ppb over a range of 0–100 % CH4 concentration background.