Work

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

Year: 2022

Type: article

Abstract: 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.

Source: Chinese Optics Letters

DOI: 10.3788/col202220.093001