Chinese Optics Letters, Volume. 5, Issue 9, 552(2007)
Behaviors of harmonic signals in wavelength-modulated spectroscopy under high absorption strength
Behaviors of harmonic signals in wavelength modulation spectroscopy (WMS) for gas detection with Lorentzian line under high absorption strength are investigated. Approximate analytic expressions of the second, fourth, and sixth harmonics on the strength are presented in concise forms. Simulations show that the expressions are in agreement with the Fourier expansion by numerical integration. It is expected theoretically and experimentally in a WMS system for methane detection that there are not only a maximum, but also a null point in the harmonics versus strength relations, which should be of practical importance in methane sensing applications.
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Yuntao Wang, Haiwen Cai, Jianxin Geng, Zhengqing Pan, Dijun Chen, Zujie Fang. Behaviors of harmonic signals in wavelength-modulated spectroscopy under high absorption strength[J]. Chinese Optics Letters, 2007, 5(9): 552