Fig. 1. Interference fringes curves for different phases

Fig. 2. Average spectra across different phase ranges

Fig. 3. Harmonic signal spectra at different frequencies.(a) First harmonic peak shift; (b) Second harmonic peak shift

Fig. 4. Comparison of second harmonic peak distortions for averaged data points at 2k, 3k, and 4k

Fig. 5. Linear spectral response function

Fig. 6. Schematic diagram and physical diagram of the CH₄ detection system

Fig. 7. Contrasting optical interference fringe reduction efficiency between two intensity groups using conventional averaging and advanced suppression techniques

Fig. 8. Histogram of measurement deviation for CH₄ at a mass concentration of 20 mg/L

Fig. 9. (a) Comparison of conventional averaging and novel suppression method for concentration stability;(b) Allan deviation analysis of detection sensitivity