Fig. 1. Off-axis integral cavity output spectrum device diagram and physical diagram

Fig. 2. Single acquisition signal

Fig. 3. Relative error of integral area with different average times and direct absorption signal after 1 000 times average

Fig. 4. Linearity analysis of the system

Fig. 5. Stability analysis

Fig. 6. Sensor system response

Fig. 7. Measurement of indoor CO₂ for four consecutive days