Fig. 1. Structure of the optical path tracking system

Fig. 2. Optical path diagram of the off-axis plane. (a) Schematic diagram of the off-axis beam; (b) magnified schematic diagram of off-axis beam

Fig. 3. Wavenumber shift of the off-axis light spectrum

Fig. 4. Optical path diagram of the SOF system

Fig. 5. Physical diagram of the system

Fig. 6. Position of the interference spot. (a) Normal condition; (b) off-axis condition

Fig. 7. Relative intensity of the interference spot. (a) Normal condition; (b) off-axis condition

Fig. 8. Footprint of the interference spot. (a) Normal condition; (b) off-axis condition

Fig. 9. Change curve of the interference intensity. (a) Static measurement; (b) dynamic measurement

Fig. 10. SNR of the spectrum. (a) Static measurement; (b) dynamic measurement

Fig. 11. Partial image of infrared spectrum. (a) SF₆; (b) measured spectrum and H₂O

Fig. 12. Wavenumber drifts of the measured spectra of SF₆ and H₂O. (a) Static measurement; (b) dynamic measurement

Fig. 13. Gas mass concentrations inversion by infrared spectra before and after correction. (a) Static measurement; (b) dynamic measurement