针对准连续激光调制吸收光谱谐波信号的解调, 设计了一种专用的准连续软件锁相放大器, 对采集的数据做有效性判断、 无效数据滤除、 数字相敏检测、 数字滤波等处理, 实现了准连续激光调制吸收光谱的谐波信号解调。 构建气体检测实验系统, 对准连续软件锁相放大器和商品化的高性能锁相放大器进行了对比实验, 结果表明, 使用准连续软件锁相放大器的Allan方差比后者小1个数量级、 检测限低2倍。 并能够解决小占空比时的信号失锁问题, 具有小的信号波形失真。

A software phase-locked amplifier demodulation method is proposed in order to demodulate the second harmonic (2f) signal of quasi-continuous laser wavelength modulation spectroscopy (WMS) properly, based on the analysis of its signal characteristics. By judging the effectiveness of the measurement data, filter, phase-sensitive detection, digital filtering and other processing, the method can achieve the sensitive detection of quasi-continuous signal. The method was verified by using carbon dioxide detection experiments. The WMS-2f signal obtained by the software phase-locked amplifier and the high-performance phase-locked amplifier (SR844) were compared simultaneously. The results show that the Allan variance of WMS-2f signal demodulated by the software phase-locked amplifier is one order of magnitude smaller than that demodulated by SR844, corresponding two order of magnitude lower of detection limit. And it is able to solve the unlocked problem caused by the small duty cycle of quasi-continuous modulation signal, with a small signal waveform distortion.