Highly sensitive HS-LITES sensor with 80 m fiber-coupled multi-pass cell based on optical path multiplexing technology.

This paper presented a highly sensitive light-induced thermoelastic spectroscopy (LITES) sensor for detecting hydrogen sulfide (H₂S) gas. Optical path multiplexing (OPM) technology was implemented within the fiber-coupled multi-pass cell (MPC) to realize ∼ 80 m gas absorption optical path length (OPL), compensating the weak absorption coefficient of HS in the near-infrared band. A circle-head quartz tuning fork (QTF) with resonant frequency of ∼ 9.5 kHz was adopted in the H₂S-LITES sensor to enhance the energy accumulation time and the detection ability. Compared with commercial QTF, signal-to-noise ratio (SNR) based on circle-head QTF was improved by a factor of 3.36 times. Minimum detection limit (MDL) for HS detection was measured to be 238.8 ppb. When the integration time of the system was increased to 250 s, the MDL could be improved to 19.8 ppb.