Spherical Acoustic Resonator-Based Quartz-Enhanced Photoacoustic-Photothermal Dual Spectroscopy Sensing

In this paper, a single-quartz-enhanced photoacoustic-photothermal dual spectroscopy sensor based on a spherical acoustic resonator (SAR) is reported for the first time. The dual spectroscopy of quartz-enhanced photoacoustic spectroscopy (QEPAS) and quartz-enhanced photothermal spectroscopy (QEPTS), utilizing a single quartz tuning fork (QTF), eliminates the frequency mismatch issue that occurs when multiple QTFs are used. The dual spectroscopy model was constructed using the finite element method, which provides numerical simulation support for subsequent experiments. The first-order radial resonant frequency of the SAR was designed to match the resonant frequency (<i>f</i>₀) of the QTF for resonance enhancement, and the radius of the SAR was determined as 27.48 mm from both theoretical and simulation analyses. A self-designed T-head QTF was utilized as the detector in this dual spectroscopy sensor. The performance of the dual spectroscopy sensor was verified by selecting acetylene (C₂H₂) as the target gas. Compared to the SAR-free single-quartz-enhanced photoacoustic-photothermal dual spectroscopy and the traditional QEPAS, the SAR-based single-quartz-enhanced photoacoustic-photothermal dual spectroscopy demonstrated 5.24-fold and 26.94-fold improvements in signal level, respectively. Allan deviation analysis revealed that the sensor's minimum detection limit (MDL) could reach 70.75 ppb with an average time of 500 s.