Natural logarithm wavelength modulation spectroscopy  

作　　者：Shaomin Li Liqun Sun 李绍民;孙利群(State Key Laboratory of Precision Measurement Technology and Instruments,Department of Precision Instruments,Tsinghua University,Beijing 100084,China)

机构地区：[1]State Key Laboratory of Precision Measurement Technology and Instruments,Department of Precision Instruments,Tsinghua University,Beijing 100084,China

出　　处：《Chinese Optics Letters》2021年第3期58-63,共6页中国光学快报（英文版）

基　　金：supported by the National Key Research and Development Program of China (No. 2018YFF0109600)。

摘　　要：Natural logarithm wavelength modulation spectroscopy(ln-WMS) is demonstrated in this Letter. Unlike the conventional wavelength modulation spectroscopy(WMS)-2 f technique, it is a linear method even for large absorbance, which is the core advantage of ln-WMS. The treating method used in ln-WMS is to take the natural logarithm of the transmitted intensity. In order to determine the proper demodulation phase, the η-seeking algorithm is introduced, which minimizes the absolute value of the first harmonic within the non-absorbing region. Subsequently, the second harmonic of the absorption signal is extracted by setting the demodulating phase as 2η. To illustrate the validity of ln-WMS, it was applied to water vapor experimentally. The result shows that even if the absorbance(base-e) is between 1.60 and 6.26, the linearity between ln-WMS-2 f and volume fraction is still established. For comparison, measurement with conventional WMS-2 f was also done, whose response no longer kept linearity. The η values retrieved in continuous measurements and the residuals were shown so as to evaluate the performance of the η-seeking algorithm. Time consumed by this algorithm was roughly 0.28 s per measurement. As an alternative WMS strategy, ln-WMS has a wide range of potential applications, especially where the absorbance is large or varies over a wide area.

关 键 词：wavelength modulation spectroscopy natural logarithm wavelength modulation spectroscopy tunable diode laser absorption spectroscopy large absorbance 

分 类 号：O433[机械工程—光学工程]