Fig. 1. Flow chart of model building

Fig. 2. Simulated results. (a) Absorbance; (b) harmonic signal

Fig. 3. Raw signals. (a) Absorption signal; (b) calibration signal

Fig. 4. Absorbance and absorption center

Fig. 5. Frequency-time response of laser

Fig. 6. Absorption simulated on two databases

Fig. 7. Simulated absorbance at different pressures with and without considering near absorption

Fig. 8. Harmonic signals simulatedat different pressures with and without considering near absorption. (a) 1 atm; (b) 10 atm

Fig. 9. Diagram of experimental setup

Fig. 10. Signals of 2f/1f with background subtracted. (a) Central frequency is 7185.60 cm-1; (b) central frequency is 6807.83 cm-1

Fig. 11. Set and measured temperatures