Parts-per-billion-level detection of hydrogen sulfide based on near-infrared all-optical photoacoustic spectroscopy

A highly sensitive trace hydrogen sulfide (H2S) gas sensing scheme based on all-optical photoacoustic spectroscopy is demonstrated. A high-power erbium-doped fiber amplified near-infrared laser is used as a light source for acoustic excitation. Meanwhile, the second-harmonic photoacoustic signal is measured by a fiber-optic cantilever microphone which is equipped with a white-light interferometric readout. For sensitivity improvement, the demodulated digital photoacoustic signal is processed by a virtual lock-in amplifier. The continuous H2S measurement experiment shows the ability of real-time response. A detection limit is achieved to be 33 ppb with a 10 s measurement time at the wavelength of 1576.29 nm. With both the excitation light and the probe light being transmitted by optical fibers, the designed sensing system has the advantages of remote detection and immunity to electromagnetic interference.