Fig. 1. Schematic diagram of cavity ring-down spectroscopy

Fig. 2. Schematic diagram of measurement system

Fig. 3. Simulated absorption spectra of CO₂， CH₄ and H₂O

Fig. 4. Structure of resonator

Fig. 5. Temperature control module

Fig. 6. Changes in gas temperature （a） and pressure （b） in the cavity over 24 hours

Fig. 7. Continuous measurement of ring-down time without absorption

Fig. 8. Allan variance analysis

Fig. 9. Correspondence between measured concentration of the system and standard gas concentration

Fig. 10. Results of comparison test between system and Picarro