Infrared dual-gas CH₄/C₂H₂ sensor system based on dual-channel off-beam quartz-enhanced photoacoustic spectroscopy...

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 × 2 × 1 cm³. 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 ∼ 7.63 parts-per-million in volume (ppmv) for CH₄ and a level of ∼ 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 × 10^-8 cm^-1·W·Hz^-1 and 3.73 × 10^-8 cm^-1·W·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 ∼ 0.73 ppmv and an MDL of ∼ 1.60 ppmv with a 100 s averaging time were achieved for CH₄ and C₂H₂, respectively.