Infrared dual-gas CH4/C2H2 sensor system based on dual-channel off-beam quartz-enhanced photoacoustic spectroscopy and time-division multiplexing technique

Highly sensitive and stable measurement of methane (CH4) and acetylene (C2H2) based on a novel dual-channel off-beam quartz-enhanced photoacoustic spectroscopy and time-division multiplexing technique was realized by a compact 3D-printed gas cell with a size of 3 x 2 x 1 cm(3). Two near-infrared distributed feedback diode lasers were employed to target the CH4 absorption line at 6046.9 cm 1 and the C2H2 absorption line at 6521.2 cm (1), respectively. Second-harmonic wavelength modulation spectroscopy method was used for photoacoustic signal recovery. A minimum detection level of similar to 7.63 parts-per-million in volume (ppmv) for CH4 and a level of similar to 17.47 ppmv for C2H2 were achieved with a 1 s lock-in integration time, leading to a normalized noise equivalent absorption (NNEA) coefficient of 7.24 x 10(-8) cm (1)center dot W center dot Hz (1) and 3.73 x 10(-8) cm 1 center dot W center dot Hz (1) for CH4 and C2H2, respectively. Allan-Werle deviation analysis was employed to evaluate the stability and the minimum detection limit (MDL) of the developed photoacoustic CH4/C2H2 dual-gas photoacoustic sensor. Owing to the high stability of the developed sensor system, an MDL of similar to 0.73 ppmv and an MDL of similar to 1.60 ppmv with a 100 s averaging time were achieved for CH4 and C2H2, respectively.