Non-resonant quartz-enhanced photoacoustic spectroscopy

In this paper, a non-resonant quartz-enhanced photoacoustic spectroscopy (NR-QEPAS) sensor is reported for the first time, to the best of our knowledge. The non-resonant photoacoustic cell (PAC) serves as the region where the photoacoustic effect occurs. NR-QEPAS offers several advantages, including flexible quartz tuning fork (QTF) positioning, frequency-matching-free operation, and simplified optical alignment. A self-designed T-head QTF was utilized as an acoustic wave transducer. The sound pressure characteristics of the non-resonant PAC were simulated using the finite element method. A near-infrared distributed feedback (DFB) diode laser with a wavelength of 1650.96 nm was selected as the excitation source. Methane (CH₄) was chosen as the target gas to validate the designed sensor’s performance. The experimental results showed that the designed non-resonant PAC worked in the plane wave state, and the sound pressure in the cavity was nearly uniform. The minimum detection limit (MDL) of the designed NR-QEPAS sensor for CH₄ detection could be 1.09 ppm (1 ppm = 10⁻⁶) when the average time was 760 s.