Electrical and optical emission characteristics of radio-frequency-driven hollow slot microplasmas operating in open air

We employ hollow slot electrodes, with pd values of ∼10 Torr cm and average E/N values of ∼70 Td, to create plasmas in open air. We measure the 13.56 MHz Irf–Vrf electrical characteristics of the plasma. Stable discharges, with sinusoidal currents, are obtained up to power densities of 14 kW/cm3, and root-mean-square radio-frequency (rf) currents of 1.5 A/cm of slot length, before nonsinusoidal currents and rf glow-to-arc transitions occur. We report the absolute optical emission in the vacuum ultraviolet region located between 110 and 155 nm, with a focus on the 149 nm atomic nitrogen line. For this atomic N line alone, we find an emitter efficiency of 0.0024.