微腔拍频光声光谱技术研究

Trace gas detection technology has wide applications in multiple disciplines. Photoacoustic spectroscopy (PAS) is a useful technique for trace gas analysis which has many attractive features such as large dynamic range and wavelength-independent, while it cannot meet all requirements of portability and continuous monitoring as the large volume of the PAS cell and the frequent calibration process of the PAS cell’s frequency. Beat frequency quartz-enhanced photoacoustic spectroscopy has more compact size and simpler structure than traditional photoacoustic spectroscopy, while the narrow gap between the QTF prongs constrains the size of the laser beam. Therefore, it is difficult to use the excitation sources with a lower spatial radiation quality for this technique. A novel PAS technique, miniature cell beat frequency photoacoustic spectroscopy (M-BFPAS), will be developed in this project. The technology of 3D print will be used for high precision manufacturing of the miniature photoacoustic cell. The beat frequency signal will be generated when the modulation frequency of the laser and the demodulation frequency of the PAS signal have a frequency difference of Δf with respect to the miniature photoacoustic cell resonance frequency. The resonance frequency and Q-frequency of the miniature photoacoustic cell as well as the trace-gas concentration can be obtained simultaneously by detecting the beat frequency signal. M-BFPAS provide a new approach for fast and continuous trace-gas monitoring, and it is of great scientific and practical importance.

痕量气体检测技术在多个学科中都有重要的应用。光声光谱痕量气体检测技术具有大动态范围、无波长选择性等优点，但传统光声池较大的体积以及需要对光声池共振频率反复校准的问题使传统光声光谱传感器无法满足人们日益增长的对仪器便携性和对气体浓度连续测量的需求。拍频石英增强光声光谱技术虽然解决了传感器小型化难题，但音叉振臂间较窄的光学通道限制了光束质量较差或功率较高的光源在该技术中的应用。本项目拟将拍频光声光谱技术、微型光声池以及3D打印技术结合，发展一种新型光声光谱技术——微腔拍频光声光谱技术。其基本原理是利用3D打印技术实现微型光声池的高精度制备，通过使激励光源的调制频率以及光声信号的解调频率失谐于微型光声池共振频率的方法获得拍频信号，从而实现对痕量气体浓度、微型光声池共振频率及品质因数的同步检测。微腔拍频光声光谱技术为痕量气体快速连续监测提供了一种新的探测手段，具有重要的科学意义和潜在的应用价值。

痕量气体检测作为核心技术在大气污染监控、工业过程控制、无创医疗诊断、爆炸物远程分析、载人航天航空等多个领域均有重要的应用。光声光谱技术是众多痕量气体检测技术的一种，不仅是一种零背景探测技术，而且有着探测灵敏度与探测光功率成正比的特性。但传统光声池较大的体积以及需要对光声池共振频率反复校准的问题使传统光声光谱传感器无法满足人们日益增长的对仪器便携性和对气体浓度连续测量的需求。本项目发展的微腔拍频光声光谱技术通过将拍频光谱技术及3D打印制备微腔技术的结合，解决了上述不足，实现了痕量气体浓度、微型光声池共振频率及品质因数的同步检测。在本项目执行中，主要建立了微腔拍频光声光谱理论模型，研究了微型光声池结构及参数配置对光声信号的影响，完善了微型光声池精密加工及平滑处理工艺，而后基于理论及实验结论搭建了微型光声气体传感器并对各项参数进行了优化。实验结果显示基于微型光声池的拍频光声光谱传感器的归一化噪声等效吸收系数可达3.9e-10 W·cm−1/√Hz，较采用传统光声光谱技术的装置性能提升了一个数量级，其响应时间也较传统光声光谱技术被优化了2个数量级。本项目资助研究的微腔拍频光声光谱技术，为痕量气体快速连续监测提供了一种新的探测手段，对于促进激光光谱技术的发展具有非常重要的科研价值。