Fig. 1. Schematic of measuring etalon signal Iv(t), absorption signal ItM(t) and background signal I0M(t)

Fig. 2. Simulated variation of R2f/p' with mole fraction of CO2

Fig. 3. Simulated variation of R2f/p' with temperature

Fig. 4. Doppler width, collisional width and Voigt width at different temperatures

Fig. 5. Flow chart of iterative calculation using calibration-free one-line method

Fig. 6. Relative sensitivity RΔVD of R(50) spectrum line at different temperatures

Fig. 7. Schematic of experimental setup

Fig. 8. Simulated (a) R2f/1f and (b) R2f/p' located at R(50) spectrum line at different mole fractions of CO2

Fig. 9. Iterative calculation of temperature and mole fraction of CO2. (a) Measured and fitted R2f/p'; (b) relative residual; (c) measured R2f/1f; (d) iterative convergence process of temperature;(e) iterative convergence process of mole fraction of CO2

Fig. 10. Measured (a) R2f/p' and (b) R2f/1f at different temperatures

Fig. 11. Measured results using calibration-free one-line method. (a) Measured temperature; (b) xm/xa