TDLAS技术中谐波信号的理论推导与实验研究

Abstract

本文对可调谐二极管激光吸收光谱技术中的激光瞬时光强进行了数值模拟和物理实验验证，确定了波长调制法中激光瞬时光强的准确表达式，并由此推导出全新的谐波信号通项表达式，分析了被检信号与参考信号间的相位差对谐波信号的影响。在实验室条件下利用CO2分子位于6527.64 cm–1的吸收谱线进行了测量实验。测量结果表明，激光瞬时光强的调制幅度在扫描过程中固定，不随扫描平均光强而变化；被检信号与参考信号间的相位差会对谐波信号的幅值和相位产生影响，在气体浓度和温度测量中不可忽略。 In this paper, we derived the expression for the instantaneous intensity based on numerical simulation and practical experiments in tunable diode laser absorption spectroscopy, and determined the new expression of the harmonic signals in wavelength modulation spectroscopy, then we analyzed the influence to the harmonic signals caused by the phase shifts between the detected and reference signals. The transition of CO2 at 6527.64 cm–1 was selected for the practical experiments, and the experimental results indicated that, the amplitude of laser intensity modulation was invariant during the scanning process, which did not change with the average scanning laser intensity. What’s more, the amplitude and phase of the harmonic signals were influenced by the phase shifts between the detected and reference signals, which cannot be ignored in gas concentration and temperature measurements.