Simultaneous dual-gas photoacoustic detection by laser modulation multiplexing in a single cell

A dual-gas detection photoacoustic system is proposed based in distinct modulation frequency of two lasers sources in a single photoacoustic optical cell. In this system, two different lasers are used, tuned at 405 nm and 1648.2 nm, corresponding to the absorption lines of NO
₂
and CH
₄
, respectively. The lasers are modulated in vicinity of the resonance of the photoacoustic cavity with the frequencies 6750 and 6850 Hz, respectively. Two microphones are used to detect the acoustic signals that are demultiplexed by a fast Fourier transform to separately quantify its concentrations.