为了提高全光式石英增强型光声光谱(QEPAS)珐珀解调系统的微弱信号检测能力,设计了一种基于MAX274的有源带通滤波电路和基于AD620的前置放大电路对信号进行预处理,同时利用LabVIEW设计了正交矢量型数字锁相技术的信号处理模块。实验结果表明,该方法能从强背景噪声中获得比较微弱的光声信号,在常温常压下对空气中的水汽含量进行探测,得到其归一化噪声等效吸收系数为1.37×10-6 cm-1 W/Hz1/2。该方法具有结构简单、价格低廉、便于操作和控制、实用性强等特点。

In order to improve the weak signal detection ability for the all-optical quartz enhanced photoacoustic spectroscopy(QEPAS) system, the active band-pass filter based on MAX274 and pre-amplifier based on AD620 are designed. The signal processing module based on orthogonal vector lock-in technology is designed with a software program of LabVIEW. The experimental results show that the weak photoacoustic signals can be picked up accurately from the strong background noise by using the method above mentioned. The experiment for detection of water vapour is carried on in the open environment. A normalized noise equivalent absorption coefficient of 1.37×10-6 cm-1 W/Hz1/2 is achieved. This method has some advantages of simple structure, low cost, easy operation and control, strong practicability, and so on.