Cavity-enhanced light-induced thermoelastic spectroscopy for trace-gas sensing.

We report a trace gas sensing technique of cavity-enhanced light-induced thermoelastic spectroscopy (CE-LITES) with a Fabry-Pérot (F-P) optical cavity and a high-quality-factor resonant quartz tuning fork (QTF). Pound-Drever-Hall (PDH) locking method is used to lock the laser to the optical cavity. With only a short 9-cm optical cavity (finesse, ∼1283) and a tiny commercially available standard QTF (Q-factor, ∼38910), a CE-LITES sensor for acetylene detection was developed to demonstrate this technique, achieving a minimum detection limit (MDL) of 7.5 parts-per-billion (ppb) for a 216-s integration time and a normalized noise equivalent absorption (NNEA) coefficient of as low as 1.91 × 10cm·W·Hz. The developed technique bears promising potential for sensitive and accurate measurement that is needed for studying trace gas-phase analyte.