Fig. 1. Schematic of gas concentration measurement equipment

Fig. 2. Experimental flow chart

Fig. 3. Variation of modulation depth over time

Fig. 4. Transmitted light intensity of reference optical path

Fig. 5. Corresponding relations between harmonic height and wavenumber offset of reference optical path

Fig. 6. Concentration inversion and residuals. (a) Gas concentration before and after correction; (b) residuals before and after correction

Fig. 7. Wavenumber offset of laser emission center

Fig. 8. Error comparison before and after correction at different offsets