Fig. 1. Schematic diagram of the internal structure of the resonant cavity

Fig. 2. Schematic diagram of test platform

Fig. 3. Breakdown threshold power of three background gases at different pressures

Fig. 4. Emission spectra of the discharge in the resonant cavity at 600 Pa under three background gases

Fig. 5. Emission spectra of different background gases when breakdown occur at pressures from 100 ~1 000 Pa

Fig. 6. Comparison of test results after water bath for O₂