以标准商用石英音叉(QTF)为测声模块的石英增强光声光谱(QEPAS)技术是近年来发展迅速的一种痕量气体检测技术。 标准商用QTF拥有的小体积, 高Q值, 高共振频率的特性使QEPAS技术具有结构紧凑且对环境噪声免疫的特性。 但传统商用QTF狭窄的振臂间距以及较高的共振频率, 使其无法在光源光束质量较差或被测气体弛豫率较低的情况下被很好的应用于QEPAS系统。 为克服上述难题, 非标准商用QTF(f0≠32.7 kHz)被设计制作并越来越多的被装配于QEPAS系统中。 因此, QTF共振频率对QEPAS系统信噪比的影响需要被详细研究。 以水汽为目标气体, 采用二次谐波调制解调技术研究了QTF共振频率对基于QEPAS技术传感器性能的影响。 实验结果表明, QTF共振频率的变化对QEPAS系统的输出信号及噪声均有显著影响且QTF共振频率与QEPAS系统信噪比之间存在反比关系。 上述结论对QEPAS系统中非标准QTF的设计及使用均具有重要的指导价值, 对该类传感器的研发及应用意义重大。

Quartz-enhanced photoacoustic spectroscopy (QEPAS) based spectrophone has developed rapidly in recent years. With the benefit of a quartz tuning fork (QTF), the QEPAS technique offerscompact structure and low sensitivity to surrounding noise. However, it’s difficult to use the standard QTF for slowly relaxing gas molecule detection as the high resonance frequencyof QTF. And it is a big challenge touse the laser with low beam quality as the excitation light sources of the QEPAS system because the gap size between the prongs of the standard QTF is too narrow. Non-standard QTFs (f0≠32.768 kHz) have been installed in QEPAS system as acoustic transducer in recent years. Therefore, the influence of the resonance frequencies of QTFs on the QEPAS system performance must be studied in detail. In this paper, the water vapor was used as the target gas and was detected via different QEPAS-based gas sensors in which the four QTFs with different resonance frequencies were installed as the acoustic transducer. The experimental results show that the resonant frequency of the QEPAS acoustic transducer has a significant effect on the signal-to-noise ratio of the QEPAS system. The reported results are extremely useful in the design of the QEPAS spectrophone.