The evolution of the optical emission pattern from a pulsed microwave-excited microstrip split-ring resonator microplasma

The evolution of the emission pattern of a pulsed microwave-excited microstrip split-ring resonator microplasma at different pressures in argon is presented. When the pressure is lower than ∼ 200 torr, the plasma fills in the gap right after the power is ON. Then, the filaments start to form on a time scale of microseconds to tens of microseconds. When the pressure is higher than ∼ 300 torr, the initial discharge region becomes much smaller with a longer filament development time. No filament is observed in helium and neon up to one atmospheric pressure. It is suggested that the diffusion and localized heating of the electrons determine the evolution of the plasma and the formation of the filaments.