A Clamp-Shaped Quartz Tuning Fork-Based Laser Spectroscopy Sensor

A novel clamp-shaped quartz tuning fork (QTF)-based laser spectroscopy sensor is reported in this paper. The clamp-type structure was created to enhance stress and temperature gradient while optimizing the distribution of surface charges in QTF-based laser spectroscopy. Additionally, this structure eliminates the sharp right angles of the QTF, thereby minimizing performance degradation caused by residual unexpected materials. The QTF features a low resonant frequency (f₀, ∼7.59 kHz) and a broad tine spacing. These characteristics contribute to an extended energy accumulation period and a simplified optical alignment process. Quartz-enhanced photoacoustic spectroscopy (QEPAS) and light-induced thermoelastic spectroscopy (LITES) were used to validate its functionality. In QEPAS and LITES simulations, the integrated surface charge of the clamp-shaped QTF was enhanced by 2.48 and 2.96 times, respectively, compared to the widely used standard QTF with an f₀ of 32.768 kHz. Experimental data indicate that the signal-to-noise ratio (SNR) of the QEPAS sensor based on the clamp-shaped QTF was improved by 1.92 times compared to the standard QTF. The signal intensity was enhanced 41.3-fold in the clamp-shaped QTF upon integration of an acoustic microresonator (AmR). When the system average time reached 1000 s, a reduction of the acetylene (C₂H₂) minimum detection limit (MDL) to 28.27 ppb was observed. In the LITES technique, the SNR of the clamp-shaped QTF-based sensor was improved by 2.45 times compared with the standard QTF, with an MDL of 251.4 ppb at a system average time of 100 s. Both theoretical simulations and experimental results in this paper clearly demonstrate the advantages of this clamp-shaped QTF in laser spectroscopy sensing.