Fig. 1. Simulated absorption spectra of CO₂ and O₂ at 1578.2--1581.8 nm

Fig. 2. Human end-tidal CO₂ detection system based on TDLAS. (a) Schematic configuration; (b) photography of system platform

Fig. 3. Experimental data collected by TDLAS system

Fig. 4. Concentration inversion process of TDLAS system. (a) Direct absorption signal of CO₂ with different concentrations; (b) 2f signal of CO₂ with different concentrations; (c) relationship between the amplitude of 2f signal and concentration of CO₂

Fig. 5. Waveform of 2f signal of CO₂ with volume fraction of 2.5%

Fig. 6. Stability of the system. (a) Measurement result of 2.5% CO₂; (b) Allan deviation of the system

Fig. 7. Human exhaled gas detection experiments. (a) Peak value of 2f signal collected during normal exhalation; (b) concentration curve of exhaled CO₂ during normal breathing in 80 s

Fig. 8. Consecutive eight times end-tidal CO₂ concentrations of five healthy adult volunteers