Comparison and excitation optimization of commercial quartz tuning forks for QEPAS

Quartz-enhanced photoacoustic spectroscopy (QEPAS) is a powerful technique for trace gas sensing, in which the quartz tuning fork (QTF) plays a key role in determining detection performance. Although custom-designed QTFs have shown enhanced sensitivity, commercially available QTFs remain attractive for practical QEPAS sensors due to their low cost and high reproducibility. In this work, four commercial quartz tuning forks with different geometrical parameters and resonance frequencies are systematically investigated for water vapor detection. The resonance characteristics of each QTF are experimentally measured, and the laser excitation position is individually optimized according to the tuning fork geometry. Using a 1,392 nm distributed feedback laser and a 1.8% H 2 O sample, the QEPAS performance of the four QTFs is compared under optimized conditions. Significant differences are observed in optimal excitation position, signal amplitude, and signal-to-noise ratio, with the standard 32.7 kHz QTF achieving the highest SNR of 430.4. These results demonstrate that commercial QTFs cannot be treated as interchangeable components and provide practical guidance for their selection and optimization in cost-effective QEPAS sensors.