Hydrogen sulfide (H₂S) is a toxic and flammable byproduct in many industrial processes. High concentrations of inhaled H₂S can cause significant discomfort and pose serious health risks, even threatening human life. Photoacoustic spectroscopy is a key technology for trace gas detection due to its advantages of zero background noise and high detection sensitivity. This paper proposes a gas sensor utilizing a distributed feedback (DFB) laser with a wavelength of 1578 nm as a light source for detecting H₂S. Additionally, the influence of varying temperatures on the resonance frequency of the photoacoustic cell and signal is investigated. We hope that the findings of the study will provide a significant reference for achieving high-precision photoacoustic spectroscopy detection under varying environmental temperatures.

A DFB laser with a central wavelength of 1578.13 nm is selected as the excitation light source. The laser power is amplified to 150 mW using an L-band erbium-doped fiber amplifier (EDFA). A multipass cell structure is employed to achieve 46 reflections of the laser in the resonant cavity, further enhancing the effective laser power. A microphone with a sensitivity of 26 mV/Pa is installed at the center of the resonant cavity to detect photoacoustic signals. The detected signal is demodulated using a lock-in amplifier and subsequently collected via a data acquisition card for processing on a personal computer (PC). Vacuum pumps and mass flow meters are used to regulate the pressure and flow rate of gas in the photoacoustic cell. To mitigate the adsorption effects of H₂S gas and prevent signal drift caused by environmental temperature fluctuations, the photoacoustic cell is heated and stabilized at 65 ℃.

At a temperature of 65 ℃, the resonance frequency of the photoacoustic cell is measured to be 888 Hz, and the quality factor of the photoacoustic cell is 17.1 (Fig. 3). The resonance frequency of the photoacoustic cell increases with increasing temperature, in line with the sound speed. The photoacoustic signal decreases with increasing temperature due to the intensified thermal motion of molecules, which leads to a reduction in their absorption intensity (Fig. 4). The photoacoustic signal of H₂S is measured in the volume fraction range of 100×10^-6?1000×10^-6[Fig. 6 (a)], confirming a linear relationship between the signal intensity and volume fraction , with a correlation coefficient of 0.9993 [Fig. 6 (b)]. Allan variance analysis shows that the sensor detection limit is 1.8×10^-6 with an integration time of 278 s (Fig. 7).

A gas sensor based on resonant photoacoustic spectroscopy is proposed for the detection of H₂S gas. This study investigates the effects of ambient temperatures on the resonance frequency of the photoacoustic cell and signal. It is found that the resonance frequency of the photoacoustic cell is directly proportional to the ambient temperature, whereas the amplitude of the photoacoustic signal exhibits an inverse relationship with temperature. By optimizing key parameters, such as laser modulation depth and modulation frequency, a detection limit of 1.8×10^-6 is achieved with integration time of 278 s. This provides a highly sensitive sensor under varying environmental temperature conditions.