Fig. 1. (a) Absorption lines of H2S in infrared region; (b) absorption lines of H2S and interfering gases in near-infrared region

Fig. 2. Schematic structure of laser photoacoustic spectroscopic system

Fig. 3. Photoacoustic signal with different modulation currents

Fig. 4. Frequency response of photoacoustic cell

Fig. 5. Photoacoustic signal as function of excitation light power

Fig. 6. (a) Second harmonic signals of H2S/SF6 gas mixture with different concentrations; (b) responses of H2S/SF6 gas mixture with different concentrations

Fig. 7. Analysis of Allan variance (inset figure: output voltage of photoacoustic system after photoacoustic cell filled with pure SF6)