Atmospheric pressure microplasma characterization

Abstract

We present electrical measurements and absolute optical emission spectra in the VUV, UV, and visible regions in order to characterize radio frequency (RF) driven hollow slot microplasmas operating in open air at atmospheric pressure. The term microplasma in our research refers to interelectrode separation (100 to 600 microns) only, as electrode lengths are scalable from 1-30 cm. The electrode geometry creates a stable extended slot plasma and associated afterglow plume. Electrical measurements and emission spectra are presented for argon and helium plasmas with small admixtures of hydrogen and nitrogen into open air. Electrical measurements characterize sheath oscillations, sheath thickness, electron density, and effects of discharge asymmetry and external circuitry. Optical emission measurements provide a qualitative understanding of plasma chemistry and kinetics, and enable quantitative determinations of key plasma parameters including gas temperature, vibrational temperature, electron temperature (plasma nonequilibirum), and electron density. We also use the optical emission spectra to compare the efficiency and magnitude of light emission from the open-air microplasmas with corresponding values from commercial sealed mercury lamps in the UVB and UVC regions.