基于波长调制-直接吸收光谱方法的CO分子1567 nm处谱线参数高精度标定

直接吸收光谱(DAS)可直接测量分子吸收率函数,并通过拟合吸收率函数确定待测气体参数.波长调制-直接吸收光谱(WM-DAS)在DAS基础上,结合了波长调制光谱(WMS)中谐波分析思想,利用傅里叶变换复现吸收率函数,可有效提高吸收率函数的测量精度.本文利用WM-DAS方法结合长光程气体吸收池,在室温低压条件下,对CO分子1567 nm处R5-R11近红外弱吸收谱线吸收率函数进行了精确复现,其拟合残差标准差低至3×10^-5,随后根据测得的吸收率函数对谱线的碰撞展宽、Dicke收敛以及速度依赖的碰撞展宽系数等光谱参数进行了高精度标定,并将其与高灵敏度的连续波腔衰荡光谱(CW-CRDS)测量结果进行了比较,实验结果表明该方法与CW-CRDS测量结果具有高度一致性,更具有系统简单、测量速度快、对环境要求低等优点.

High precision calibration of spectral parameters of CO at 1567 nm based on wavelength modulation-direct absorption spectroscopy

Direct absorption spectrum(DAS)can be used to measure the molecular absorptivity function and determine the spectral parameters of the gas by fitting the measured absorptivity function.Wavelength modulation-direct absorption spectroscopy(WM-DAS)is based on DAS and combines with the idea of harmonic analysis in wavelength modulation spectrum(WMS).The measurement accuracy of absorptivity function can be effectively improved by using Fourier transform.In this paper,the absorptivity function of CO R5-R11 near infrared weak absorption line at 1567 nm is accurately reproduced by using the WM-DAS method combined with long optical path gas absorption cell at room temperature and low pressure.The standard deviation of the fitting residual reaches 3×10^-5,and then the spectral parameters such as collision broadening,Dicke narrowing and speed-dependent collision broadening coefficients are measured in high precision.These parameters are compared with the results from the high sensitivity continuous wave cavity ring down spectroscopy(CW-CRDS).The experimental results show that the signal-to-noise ratio of the absorptivity function measured by CW-CRDS is about 2.5 times that of the long-path WM-DAS,and the measured spectral parameters are highly consistent.The relative errors of the collision broadening coefficients obtained by using the Voigt profiles of the two methods are less than 1%.At the same time,the detection limit of CO at 1567 nm based on the WM-DAS method is about 80 ppb,and the corresponding absorption coefficient is 2×10^-10 cm^-1,which is slightly higher than that from the CW-CRDS method.However,the WM-DAS method has the advantages of fast measurement speed,simple system and low cost,and is expected to provide a new method of measuring the weak absorption lines.