A high-performance light-induced thermoelastic spectroscopy sensor based on a high-Q value quartz tuning fork load

This paper reports for the first time a high-performance light-induced thermoelastic spectroscopy (LITES) sensor based on a high-quality factor (Q) quartz tuning fork (QTF) as the load. The high-Q QTF, sealed in a vacuum and featuring a Q factor of about 50000, is connected in series with a commercially available standard QTF to enable piezoelectric signal filtering, thereby increasing the overall Q-factor. Methane (CH₄), a highly flammable and explosive gas, is chosen as the target for this study. Compared to the bare QTF mode, the series QTF mode increased the Q value of the QTF detector by 2.11 times and the signal-to-noise ratio (SNR) of the CH₄-LITES sensor by 1.73 times. Under varying CH₄ concentrations, the series QTF mode-based CH₄-LITES sensor demonstrated an excellent linear response, with a calculated minimum detection limit (MDL) of 0.96 ppm. According to Allan deviation analysis, the MDL of the CH₄-LITES sensor was improved to 0.16 ppm when the average time of the system was 100 s. Additionally, to assess the frequency selectivity of the series QTF mode, external acoustic waves with a center frequency of 32.768 kHz were used for interference testing. The SNR of the bare QTF mode decreased by a factor of 108.92, while the SNR of the series QTF mode only decreased by a factor of 26.88. These results show that the series QTF mode provides 4 times greater anti-noise capacity, significantly enhancing the frequency selectivity of the LITES sensor.