非标定波长调制吸收光谱气体测量研究

为消除可调谐激光调制吸收光谱气体测量技术对于标定过程的依赖,研究了二次谐波信号的非标定波长调制气体测量方法.通过对测量的二次谐波线型进行分析,给出相同工况下二次谐波模拟信号,并利用测量与模拟二次谐波信号进行线性拟合直接计算气体浓度.实验室内采用非标定波长调制气体测量方法,利用 6336.24 cm^-1处特征吸收谱线对10 cm长气体吸收池内的CO₂进行了测量.结果表明,非标定波长调制气体测量方法可适应各种不同条件,适合于现场气体在线测量.当调制系数在1.8—3. 关键词： 波长调制 二次谐波 吸收光谱 半导体激光器

Calibration-free wavelength modulation absorption spectrum of gas

The calibration-free wavelength modulation absorption spectrum is studied based on the second harmonic (2f) signal to remove the calibration procedure for tunable diode laser absorption gas sensing. The simulated 2f signal is obtain from the analysis of peak and trough from measured 2f signal line shape. The gas concentration is calculated by the linear fitting of measured and simulated 2f signals. The experiment on CO₂ detection is carried out at transition of 6336.24cm^-1 in a 10 cm absorption cell. The results prove that the calibration-free wavelength modulation absorption spectrum is suited for on-site gas sensing at various conditions. The average absolute error of gas concentration is 0.67% at modulation index ranging from 1.8 to 3.2. With gas concentration and pressure varied, the average absolute errors of gas concentration are measured to be about 0.98% and 0.74%.