Conventional wavelength modulation spectroscopy (WMS) is vulnerable to the influence of low-frequency noise. Accuracy of the method highly depends on the performance of the costly lock-in amplifier. In this article, we report a new and effective method for reconstructing second-harmonic signals through WMS based on fast Fourier transform (FFT). This method is less disturbed by low-frequency noise because it does not use a low-frequency ramp wave. Formulation and detection procedures were presented. The discrete second-harmonic waveform can be obtained by continuously changing the DC signal and FFT analysis in this method. Second-harmonic waveforms acquired by the two means are generally consistent. The experimental study validates the obtained gas concentration from 5% to 30%, showing a good linear relationship by the proposed method. The maximum relative error on concentration extraction is 2.87%; as for conventional WMS, this value is 4.50%. The developed measurement method may have potential in computed tomography.

Linquan Lai;Yue Chen;Kongtao Chen;Jiale Tang;Kaiwen Yin;Fuqiang Jia;Dun Qiao;Yuanlong Fan;Kang Li;Nigel Copner

Fujian Key Laboratory of Ultrafast Laser Technology and Applications, School of Electronic Science and Technology, Xiamen University, Xiamen 361005, China;Wireless & Optoelectronics Research & Innovation Centre, Faculty of Computing, Engineering & Science, University of South Wales, Wales CF37 1DL, UK

中国光学快报（英文版）

[1]Linquan Lai;Yue Chen;Kongtao Chen;Jiale Tang;Kaiwen Yin;Fuqiang Jia;Dun Qiao;Yuanlong Fan;Kang Li;Nigel Copner-.Reconstruction and fitting of second-harmonic signals by wavelength modulation spectroscopy method based on fast Fourier transform)[J].中国光学快报（英文版）,2022(09):093001

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