Fig. 1. Absorption lines of H₂S and CO₂ in the near-infrared region and the simulated 2f signals. (a) Absorption lines of H₂S and CO₂ in the near-infrared region; (b) simulated 2f signals of H₂S and CO₂

Fig. 2. Structure diagram and photo of the fiber amplification enhanced photoacoustic spectroscopy based gas detection system. (a) Structure diagram; (b) photo

Fig. 3. Relationship between photoacoustic signal amplitude and modulation current. (a) H₂S; (b) CO₂

Fig. 4. Responses of this system to 2f signals generated by H₂S/N₂ gas mixtures with different H₂S volume fractions. (a) 2f signals generated by H₂S/N₂ gas mixtures with different H₂S volume fractions; (b) peak values of the 2f signals as a function of H₂S volume fractions

Fig. 5. Responses of this system to 2f signals generated by CO₂/N₂ gas mixtures with different CO₂ volume fractions. (a) 2f signals generated by CO₂/N₂ gas mixtures with different CO₂ volume fractions; (b) peak values of the 2f signals as a function of CO₂ volume fractions

Fig. 6. Interference of CO₂ on H₂S absorption. (a) Interference absorption spectrum; (b) long-term detection of H₂S response and high-concentration CO₂ interference

Fig. 7. Allan analysis results of H₂S and CO₂. (a) Allan deviation analysis to H₂S when the photoacoustic cell is full of air, inset is long term equivalent H₂S concentration; (b) Allan deviation analysis to CO₂ when the photoacoustic cell is full of air, inset is long term equivalent CO₂ concentration