Quartz-enhanced photoacoustic spectroscopy based on the four-off-beam acoustic micro-resonator

A four-off-beam acoustic micro-resonator (AmR) structure is proposed to improve the photoacoustic signal intensity in quartz-enhanced photoacoustic spectroscopy (QEPAS) for trace gas sensing. Two vertical-array-based double-off-beam AmR structures are arranged on each side of the quartz tuning fork (QTF) horizontally to construct a four-off-beam AmR structure using a rectangular prism. This QEPAS scheme based on the four-off-beam AmR is evaluated in the water-vapor detection of air at normal atmospheric pressure and room temperature (27 °C). Comparing with the bare QTF scheme, the new QEPAS configuration enhances the photoacoustic spectroscopy signal by a factor of 25.84 times, achieving a minimum detection limit of 278 ppbv with a normalized noise equivalent absorption coefficient of 1.27 × 10−9 W/Hz1/2 in water vapour detection at a wavelength of 1368.597 nm.