Fig. 1. SOP temperature measurement system

Fig. 2. Calibration data of calibration lamp in system

Fig. 3. Wavelength calibration of laser

Fig. 4. Discharge spark measurement experiment results

Fig. 5. Spark spectrum changes when the voltage is 8000 V and the gap is 0.5 mm

Fig. 6. Fitting result of the discharge spark temperature changes with time when the gap is 0.5 mm and the voltage is 8000 V

Fig. 7. Change of spectrum with time under different voltages when the gap is 0.5 mm

Fig. 8. Spark spectrum at each voltage at 1.02 μs under the condition of 0.5 mm gap

Fig. 9. Change of discharge plasma temperature with time under different voltages

Fig. 10. Change of spectrum with time under different gaps when the voltage is 10000 V

Fig. 11. Spark spectrum at each gap at 1.02 μs under the condition of 10000 V voltage

Fig. 12. Change of discharge plasma temperature with time under different gaps