title: Logarithmic conversion of absorption detection in wavelength modulation spectroscopy with a current-modulated diode laser.
abstract: Logarithmic-conversion data processing used in wavelength modulation spectroscopy (WMS) with a current-modulated diode laser as its source is analyzed and compared with second-to-first ratio detection. Analytic Fourier coefficients of logarithmic-converted residual amplitude modulation (RAM) of a light source are given. An experimental setup for methane absorption detection at 1650 nm is described. It is shown theoretically and experimentally that logarithmic-converted WMS cannot only eliminate the fluctuation of received light power, but also improve the signal-to-noise ratio significantly.
authors.affiliation: Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Science, Shanghai 201800, China. fica@163.com
authors.forename: Yuntao
authors.initials: Y
authors.lastname: Wang
authors.forename: Haiwen
authors.initials: H
authors.lastname: Cai
authors.forename: Jianxin
authors.initials: J
authors.lastname: Geng
authors.forename: Zujie
authors.initials: Z
authors.lastname: Fang