Reconstruction and fitting of second-harmonic signals by wavelength modulation spectroscopy method based on fast Fourier transform

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