Harmonic wavelet analysis of TDLAS signals

Wavelength modulation spectroscopy (WMS) technique uses high-frequency modulation signal which is superimposed on the slow scanning signal. The signal is applied to the semiconductor laser drive current, so the laser frequency linear sweep as well as the modulation sweep. The absorption intensity of the lines is also modulated by the same frequency. 2f signal extraction of WMS was achieved by harmonic wavelet, which is the tool for data demodulation. The absorption spectroscopy data was obtained by scanning the beams from a tunable diode laser operating near the 7 185.6 cm-1 with the modulation frequency of 180 kHz. The 2f signal of high quality was obtained after harmonic wavelet processing for the data. The 2f signal's identification of its peak center is very clear, and data smoothness, anti-interference ability of the signal is better than method of digital lock-in.