Light-induced thermoelastic sensor for ppb-level H₂S detection in a SF₆ gas matrices exploiting a mini-multi-pass...

We present an optical sensor based on light-induced thermoelastic spectroscopy for the detection of hydrogen sulfide (H₂S) in sulfur hexafluoride (SF₆). The sensor incorporates a compact multi-pass cell measuring 6 cm × 4 cm × 4 cm and utilizes a quartz tuning fork (QTF) photodetector. A 1.58 µm near-infrared distributed feedback (DFB) laser with an optical power of 30 mW serves as the excitation source. The sensor achieved a minimum detection limit (MDL) of ∼300 ppb at an integration time of 300 ms, corresponding to a normalized noise equivalent absorption coefficient (NNEA) of 3.96 × 10^-9 W·cm^-1·Hz^-1/2. By extending the integration time to 100 s, the MDL can be reduced to ∼25 ppb. The sensor exhibits a response time of ∼1 min for a gas flow rate of 70 sccm.