Direct laser-based measurements of the collisional depopulation rate of the n=2 level of hydrogen in a plasma

Abstract

A laser-based method of preparing a plasma with only a single atomic-state population significantly out of equilibrium is described. This technique allows determination of collision rates for first excited states largely free from the problems of multiple-level excitation and cascade inherent in most fluorescent scattering techniques in plasmas, or from the absolute intensity measurements in the VUV inherent in emission spectroscopic techniques. The results obtained for the n=2 state of hydrogen, however, pose severe problems in interpretation in terms of presently accepted electron collision rates.