On–off-beam differential resonance quartz-enhanced photoacoustic spectroscopy gas sensing technology

In this paper, a novel trace gas sensor based on on–off-beam differential resonance quartz-enhanced photoacoustic spectroscopy (ODR-QEPAS) is proposed. Relying on the differential characteristics of the acoustic resonance tube and integrating the advantages of two classic optical configurations (on-beam and off-beam) simultaneously, this structure realizes dual resonant enhancement of the photoacoustic signal. The finite element analysis (FEA) method was adopted to calculate the acoustic field distribution, which provides solid numerical support for the experimental investigation. Acetylene (C 2 H 2 ) was selected as the target analyte to characterize the sensor performance, and the geometric parameters of the differential resonance tube were optimized. Under identical experimental conditions, the proposed ODR-QEPAS system outperforms the traditional bare QTF-based system, yielding an 18.92-fold increase in 2 f signal amplitude, a 36.8% reduction in noise floor, and a 29.61-fold improvement in signal-to-noise ratio (SNR).