基于QEPAS技术的乙炔微量气体高灵敏度检测研究

石英增强光声光谱(QEPAS)是近年来发展起来的一种痕量气体探测技术，具有系统体积小、价格低廉、探测灵敏度高等优点。乙炔(C₂H₂)是一种化学性质活泼的有毒气体，对它进行高灵敏度检测在变压器故障诊断、环境监测等领域有着重要的意义，基于此，采用QEPAS技术对C₂H₂微量气体展开高灵敏度检测研究。采用输出波长为1.53 μm的连续波分布反馈半导体激光器作为激发光源。为了提高信噪比和简化数据处理过程，QEPAS传感器系统采用波长调制和2次谐波探测技术。为了提高QEPAS系统信号幅值，相比于常见的共振频率为32.768 kHz的石英音叉，采用了共振频率较低的30.72 kHz石英音叉作为声波传导器，同时还优化了石英音叉与激光束的空间位置、激光波长调制深度，并添加了声波微共振腔，选择的微共振腔长度为4 mm、内径为0.5 mm，最终获得了2.7 ppm的优异检测极限，归一化噪声等效吸收系数为1.3×10-8 cm-1·W·Hz-1/2。

Study on High Sensitive Detection of Acetylene Trace Gas Based on QEPAS

Quartz-enhanced photoacoustic spectroscopy (QEPAS)technology invented lately uses a commercially available mm sized piezoelectric quartz tuning fork (QTF)as an acoustic wave transducer.A high Q-factor and a ~30 kHz resonance frequen-cy of the QTF improve QEPAS selectivity and immunity to environmental acoustic noise.QEPAS sensor has the advantages of high sensitivity,selectivity and compactness.Acetylene (C2 H2 ),a toxic and harmful gas,has great significance in high sensitive detection in many fields such as the detection of fault gases in transformers and environmental monitoring.In this paper,QEPAS technology was employed to detect C2 H2 .A continuous-wave distributed feedback (DFB)single mode diode laser emitting at 1.53μm was used as the exciting source.In order to reduce the sensor background noise and simplify the data process,a wave-length modulation spectroscopy and a 2nd harmonic detection technique were employed.To increase the QEPAS signal ampli-tude,unlikely the usually used quartz tuning fork (QTF)with resonance frequency of 32.768 kHz,a novel QTF with 30.72 kHz was adopted as the acoustic wave tranducer.The position between laser beam and QTF and the laser wavelength modulation depth were optimized.In the meanwhile,micro-resonator was added into the QEPAS sensor system,and the length and inner di-ameter of the mR tubes were selected to be 4 mm and 0.5 mm,respectively.Finally,a 2.7 ppm minimum detection limit was obtained,and the corresponding normalized noise equivalent absorption (NNEA)coefficient was 1.3×10-8 cm-1 ·W·Hz-1/2 .