TDLAS-WMS second harmonic detection based on spectral analysis

A novel method for the detection of the second-harmonic component of tunable laser diode absorption spectroscopy-wavelength-modulated absorption spectroscopy is proposed in this study. The proposed method is based on spectral analysis, and the second-harmonic component is obtained in the frequency domain through a rectangular window. The validity, correctness, and noise immunity of the proposed method are verified through simulations and experiments. Experimental results demonstrate that the relative detection error level of the proposed method is <3%. In contrast to lock-in amplification, the proposed method does not require reference signals and low-pass filtering algorithms. These characteristics simplify data processing in the proposed method.