Research on denoising of second harmonic signal in LITES based on TVF-EMD-WTD method

Light-induced thermoelastic spectroscopy (LITES) is a critical technique for acetylene (C₂H₂) gas analysis. However, its detection accuracy is significantly compromised by noise interference. To address this issue, we propose a denoising method for the second harmonic signal in LITES, integrating time-varying filtering empirical mode decomposition (TVF-EMD) and wavelet threshold denoising (WTD). In this approach, TVF-EMD decomposes the second harmonic signal into a series of intrinsic mode functions (IMFs), then noise components are identified and removed based on the variance contribution ratio. The reconstructed signal is then further processed using WTD to enhance signal quality. The effectiveness of the proposed denoising method is confirmed by analyzing the simulated signals. The experimental results show that the algorithm can effectively improve the detection accuracy and stability of the LITES system.