基于弹光调制的红外光谱吸收法在室内VOC检测中的研究

Research on VOC Concentration Detection by Photoelastic Modulation Infrared Spectrum Absorption Method

为了保证静态干涉系统在气体定性定量分析方面稳定性高、抗干扰能力强的特点,设计了基于弹光调制实现光程静态扫描的干涉检测系统。系统由红外激光器、起偏器、弹光调制器、检偏器及CCD组成。通过弹光调制器使弹光晶体的主折射率随调制信号周期性的变化,从而产生周期性变化的光程差。通过对调制相位变化的计算,可知得到调制度随晶体长度、调制时间的函数关系。依据相位延迟及干涉图能量分布,推导了对应的干涉光强公式。实验采用硒化锌晶体作为弹光调制晶体,分别对5组不同浓度的三种常见VOC气体进行浓度分析,实验结果与传统红外吸收光谱吸收法的检测结果进行对比。弹光调制红外光谱吸收法在具备高稳定性、实时性的基础上,检测精度明显优于传统红外吸收光谱吸收法。

In order to ensure high stability and strong anti-interference ability in static interference system for qualitative andquantitative analysis of gas,a static scans interference detection system was designed based on photoelastic modulation infraredspectrum absorption system.The system consists of infrared laser,polarizer,photoelastic modulator,polarization analyzer andCCD components.By photoelastic modulator the principal refractive index of optical crystal will change cyclically by the modula-tion signal,producing cyclical changes in the optical path difference.With the calculation of modulation phase variation,the au-thors can get the function of the crystal length,the modulation cycle,and the range of optical path difference.Based on phasedelay value and the energy distribution of interference pattern,the authors got the formula for the corresponding interferencelight intensity.The experiment used ZnSe crystal as the photoelastic modulation crystal,the polarizer uses the DOP3212polariz-er,and the detector uses the TCD5390AP array CCD.The five groups have different concentrations with three common VOCgases（formaldehyde,benzene and xylene）for detecting the concentrations of gases.The experimental results with the tradition-al infrared absorption were compared with the test results of photoelastic modulation infrared spectrum absorption method.Themethod of photoelastic modulation infrared spectrum absorption had high stability and real-time features,while the detectionaccuracy is better than the traditional infrared absorption method.