Absolute UV and VUV emission in the 110–400 nm region from 13.56 MHz driven hollow slot microplasmas operating in open air

Abstract

We present absolute optical emission spectra in the 110–400 nm regions from radio-frequency-driven (13.56 MHz) hollow slot microplasmas operating in open air at atmospheric pressure. The term microplasma in our research refers to inter-electrode separation (100–600 µm) only, as electrode lengths are scalable from 1 to 30 cm. This creates an extended slot plasma and an associated afterglow plume as described herein. Spectra are presented for gas flows through the microelectrodes of argon and helium with small admixtures of hydrogen and nitrogen into open air. The spectra are discussed in terms of species origin and magnitude of the dominant emission lines. Atomic O and N lines dominate the 110–200 nm region, whereas, in the 200–400 nm region, NO, N2, and NH molecular lines are strongest. The role of the state in the open air microplasmas is discussed and the second positive system of molecular nitrogen (N2(C3Πg–B3Πg)), is used to measure the rotational (gas) temperature. Finally, we compare the efficiency and magnitude of light emission from the open air microplasmas with values attainable from commercial sealed mercury lamps in the UVB and UVC regions.