Quartz tuning fork-based demodulation of an acoustic signal induced by photo-thermo-elastic energy conversion

A gas sensing method based on quartz-enhanced photothermal spectroscopy (QEPTS) demodulated by quartz tuning fork (QTF) sensing acoustic wave is reported for the first time. Different from traditional QEPTS, the method proposed in this paper utilizes the second QTF to sense acoustic wave produced by the first QTF owing to the vibration resulted from photo-thermo-elastic effect. This indirect demodulation by acoustic wave sensing can avoid QTF being irradiated by laser beam and therefore get less noise and realize better detection sensitivity. Four different sensing configurations are designed and verified. Acetylene (C₂H₂) with a volume concentration of 1.95 % is selected as the target gas. A model of sound field produced by the first QTF vibrating is established by finite element method to explain the variation trend of signal and noise in the second QTF. The measured results indicate that this technique had an enhanced signal-to-noise ratio (SNR) of 1.36 times when compared to the traditional QEPTS. Further improvement methods for such technique is proposed.