Quartz-enhanced laser spectroscopy based on grooved quartz tuning forks: Design, optimization, and characterization

Quartz-enhanced laser spectroscopy, including quartz-enhanced photoacoustic spectroscopy (QEPAS) and light-induced thermoelastic spectroscopy (LITES), has become a research focus in the trace gas sensing field. This study developed a systematic approach for designing, optimizing, and characterizing grooved quartz tuning forks (QTFs) for quartz-enhanced laser spectroscopy. We combined theoretical modeling, finite element simulation, and experimental investigation to develop a comprehensive method for designing high-performance grooved QTFs by controlling the groove dimensions, including its depth, width, and shape. Experimental investigations revealed that rectangular grooves with a depth of 22 μm and a width of 1237.5 μm produced the strongest signals in both QEPAS and LITES systems, achieving SNR improvements of 1.45 times and 1.75 times, respectively, compared to conventional ungrooved QTFs. For isosceles-trapezoidal grooves, the positive isosceles-trapezoidal (PI) configuration consistently surpassed the inverted isosceles-trapezoidal (II) design across all tested depths. The 44 μm-deep PI grooved QTF demonstrated particularly notable performance, exhibiting the SNR value 1.71 times higher than the ungrooved QTF and 1.18 times greater than the II grooved QTF at the same depth. The 44 μm-deep PI grooved QTFs enabled detection limits of 0.56 ppm in QEPAS and 0.15 ppm in LITES systems for methane sensing. These experimental observations aligned well with theoretical predictions, confirming that groove geometry determines QTF behavior by modulating the balance between effective stiffness and mass.