基于可调谐二极管激光吸收光谱的痕量水汽测量

Measurement of Trace Water Vapor Based on Tunable Diode Laser Absorption Spectroscopy

采用可调谐二极管激光吸收光谱技术对高纯氮气中的痕量水汽进行检测。首先,在自主设计的多次反射池中,利用体积分数为1.007×10^(-3)的CH_4作为标准气体,运用1654 nm附近的CH_4吸收光谱,采用三线拟合方法同时拟合3条中心频率相近(小于0.01 cm^(-1))、低态能级相同的吸收线,测量得到多次反射池的精确光程;然后,研究可调谐二极管激光吸收光谱系统中激光器干涉背景和周围空气段的吸收本底,获得可调谐二极管激光吸收光谱系统的精确本底;最后,利用激光器波长为1854 nm的可调谐二极管激光吸收光谱系统(探测灵敏度为1.14×10^(-6))对高纯氮气中水汽的浓度进行测量,通过严格的背景吸收扣除以及多线Voigt线型模型拟合得到了无背景吸收的水汽光谱,进而获得高纯氮气中水汽的体积分数。结果表明:得到的实验高纯氮气中水汽的体积分数与国家标准规定的高纯氮气中水汽的体积分数的最大偏差为10.33%。

The tunable diode laser absorption spectroscopic technique is used for the measurement of water vapor in high purity nitrogen. Firstly, in the self-designed multiple reflectors, the accurate light path values of the multiple reflectors are measured by using the method comprising of taking CH4 with a volume fraction of 1. 007 × 10^-3 as the standard gas, the methane absorption spectrum at around 1654 nm, and the three-line simultaneous fitting of three absorption lines with the similar central frequencies （less than 0.01 cm-1） and the same low energy levels. Secondly, the laser interference background and the absorption background of ambient air in the tunable diode laser absorption spectroscopy system are studied and the accurate background of tunable diode laser absorption spectroscopy system is obtained. Finally, the water vapor concentrations in high purity nitrogen are measured by the 1854 nm tunable diode laser absorption spectroscopy system with a detection sensitivity of 1.14 × 10^-6. Through the strict background absorption deduction, the multi-line Voigt linear model is used to fit the water vapor spectrum without background absorption to obtain the water vapor concentration in high purity nitrogen. The results show that, the obtained maximum deviation is 10. 33% compared with the national standard.