Nanosecond discharge at the interfaces of flat and periodic ripple surfaces of dielectric window with air at varied pressure

The spatial visible light profiles from plasma discharges near the dielectric-air interfaces of flat and periodic triangular surfaces at varied pressure in air were studied using a high-speed ICCD camera. Intense light emitted in a sub-centimeter thickness layer above the dielectric surface was observed. With increasing pressure, the brightness and thickness of the light first increases to maximum at a pressure of about 100 Torr, and then decreases. The nonlinear variation of brightness with pressure may result from the increasing critical density of plasma with pressure while the averaged electron energy decreases with an increased rate of collision with gas atoms and molecules. At a certain range of pressure, the electron energy is close to the peak of the excitation collision cross section, together with very high electron density, leads to maximum brightness and thickness light emission. Both for the flat surface and periodic surface, the light emission duration continuously becomes shorter with increasing pressure. Compared with the flat surface, the light duration for the periodic surface is shorter, especially for pressure below 0.1 Torr, where the duration dramatically decreases and no pulse-tail erosion of breakdown waveform is found. Consequently, the duration and brightness for the flat surface is higher than those for the periodic surface in most of the pressure regime studied here. Electron energy, density, and light emission brightness are studied in the analytical electron dynamic to understand these phenomena.