Off-plane quartz-enhanced photoacoustic spectroscopy

• Huijian Luo, Junming Li, Haohua Lv, Jiabao Xie, Chenglong Wang, Haoyang Lin, Ruobin Zhuang, Wenguo Zhu, Yongchun Zhong, Ruifeng Kan, JianHui Yu, and Huadan Zheng
• received 09/25/2023; accepted 01/01/2024; posted 01/31/2024; Doc. ID 506650
• Abstract: In this work, we developed off-plane quartz-enhanced photoacoustic spectroscopy (OP-QEPAS). In the OP-QEPAS the light beam neither went through the prong spacing of the quartz tuning fork (QTF), nor in the QTF plane. The light beam is in parallel with the QTF with an optimal distance, resulting in low background noise. A radial-cavity (RC) resonator was coupled with the QTF to enhance the photoacoustic signal by radial resonance mode. By offsetting both the QTF and the laser position from the central axis, we enhance the effect of acoustic radial resonance and prevent the noise generated by direct laser irradiation of the QTF. Compared to IP-QEPAS based on a bare QTF, the developed OP-QEPAS with a RC resonator showed a >10× signal-to-noise ratio (SNR) enhancement. The OP-QEPAS system has great advantages in the use of light emitting devices (LEDs), long-wavelength laser sources such as mid-infrared quantum cascade lasers, and terahertz sources. When employing a LED as excitation source, the noise level was suppressed by ~2 orders of magnitude. Furthermore, the radial and longitudinal resonance modes can be combined to further improve the sensor performance.