Fig. 1. Coefficients of 1st-4th order harmonic components of Lorentz absorption line

Fig. 2. Physical diagram of quartz tuning fork

Fig. 3. Three-dimensional model of quartz tuning fork.(a) Size parameters of quartz tuning fork; (b) three-dimensional modeling of quartz tuning fork

Fig. 4. Vibration shapes of first six order models of the quartz tuning fork. (a) 1st order; (b) 2nd order; (c) 3rd order; (d) 4th order; (e) 5th order; (f) 6th order

Fig. 5. Comparison of absorption line intensities of hydrogen sulfide, water, and carbon dioxide

Fig. 6. Simulated absorption spectrum of hydrogen sulfide gas with volume fraction of 20×10^-6

Fig. 7. Schematic of resonant frequency scanning for quartz tuning fork

Fig. 8. Structural diagram of hydrogen sulfide gas measurement system based on QEPAS

Fig. 9. Photoacoustic signals under different concentrations of hydrogen sulfide gas

Fig. 10. Second harmonic signal of hydrogen sulfide with volume fraction of 100×10^-6