Fig. 1. Absorption spectra of CH₄ and C₂H₄

Fig. 2. Schematic of experimental system

Fig. 3. Absorption spectra of CH₄ and C₂H₄ at 100 mbar. (a) Absorption spectra of CH₄ and C₂H₄ in wide scanning range; (b) absorption spectrum of C₂H₄ after reducing wavelength scanning range

Fig. 4. Pressure data, frequency distribution histogram, and Gaussian fitting result. (a) Pressure data; (b) frequency distribution histogram and Gaussian fitting result

Fig. 5. Absorption spectra, measurement linearity values and errors of C₂H₄ with different volume fractions. (a) Absorption spectra of C₂H₄ with different volume fractions; (b) measurement and linear fitting results; (c) absolute error

Fig. 6. Absorption spectrum of C₂H₄ with volume fraction of 10×10^-6

Fig. 7. Test results of response time

Fig. 8. Allan variance analysis results. (a) Volume fraction of C₂H₄; (b) Allan variance