Elliptical acoustic resonator-enabled synchronous acoustic excitation by multiple laser beams in quartz-enhanced photoacoustic spectroscopy

We report synchronous excitation of an acoustic mode in quartz-enhanced photoacoustic spectroscopy (QEPAS) enabled by an elliptical acoustic resonator under multi-beam illumination. In this configuration, multiple laser beams distributed within the prong gap of a quartz tuning fork (QTF) coherently excite the same acoustic mode, leading to efficient acoustic energy confinement and enhanced coupling to the QTF. Finite-element simulations based on distributed line acoustic sources reveal that, compared with the resonator-free case, a half-wavelength acoustic resonator enhances the effective acoustic excitation by a factor of approximately 4, while a three-quarter-wavelength resonator provides a higher enhancement of about 7. These predictions are experimentally validated using a multi-pass cell-based QEPAS system incorporating an elliptical acoustic resonator. The results demonstrate that resonator-enabled synchronous multi-beam excitation reshapes the acoustic coupling behavior in QEPAS and provides a practical route toward high-sensitivity photoacoustic sensing beyond optical field-limited enhancement.