Kinetic studies of ionic excimers

Abstract

Ionic excimers are potential candidates for storage media in vacuum ultraviolet (VUV) lasers. In order to study their production mechanisms the VUV fluorescence was observed after exciting corresponding gas mixtures by an intense coaxial electron beam. The deposited energy was increased up to 100 mJ/cm3 bar (Ar). Out of three classes of ionic excimers the species Ar2+2 (190 nm), Ne+Kr (166, 184 nm), and Kr+K (135 nm) were studied in detail. In the case of Kr+K buffer gas He with a pressure up to 30 bar was added in order to increase the fluorescence intensity. Measurements were performed at various gas densities. At optimum conditions with respect to the quantum efficiency ηQ, values of ηQ=8.5×10−2, 4×10−2, and 3×10−2, respectively, were determined. At pumping densities in the order of 10 mJ/cm3 the quantum yield already decreases. The maximum achievable fluorescence energy was found to be 40, 30, and 10 μJ/cm3, respectively. By comparing the results with predictions of rate equation models rate constants for the most important reactions were obtained. It was shown that quenching processes of the excimer molecules and precursor ions by neutrals and/or plasma electrons limit the obtainable excimer densities below values necessary to achieve optical gain.