利用可调谐激光二极管吸收光谱技术进行气体检测时, 波长调制伴随的光强幅度调制, 会使解调出的谐波谱线发生畸变。 在傅里叶分析的基础上对可调谐激光二极管吸收光谱任意调制幅度的波长调制光谱信号进行了分析, 给出了光强幅度调制引起吸收谱线畸变的理论解释。 提出了在波长调制过程中进行同步平抑幅度调制的方法来消除谱线畸变, 设计了实验方案并进行了二氧化碳气体实验验证。 实验表明, 平抑后的残余光强调制幅度约比补偿前降低了3个数量级, 气体吸收谱线二次谐波畸变量比补偿前降低了92％。 该方法在有效校正光谱线畸变的同时, 降低了对系统中光电探测器、 滤波器、 数模转换器等环节的动态范围要求, 具有在工业现场痕量气体在线监测系统中推广应用的潜力。

In the present paper, the signal of a tunable diode laser absorption spectroscopy (TDLAS) trace gas sensing system, which has a wavelength modulation with a wide range of modulation amplitudes, is studied based on Fourier analysis method.Theory explanation of spectrum distortion induced by laser intensity amplitude modulation is given.In order to rectify the spectrum distortion, a method of synchronous amplitude modulation suppression by a variable optical attenuator is proposed.To validate the method, an experimental setup is designed.Absorption spectrum measurement experiments on CO2 gas were carried out.The results show that the residual laser intensity modulation amplitude of the experimental system is reduced to ~0.1% of its original value and the spectrum distortion improvement is 92% with the synchronous amplitude modulation suppression.The modulation amplitude of laser intensity can be effectively reduced and the spectrum distortion can be well corrected by using the given correction method and system.By using a variable optical attenuator in the TDLAS (tunable diode laser absorption spectroscopy) system, the dynamic range requirements of photoelectric detector, digital to analog converter, filters and other aspects of the TDLAS system are reduced.This spectrum distortion correction method can be used for online trace gas analyzing in process industry.