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Dark space diagnostics with laser photoionization and Galvanic detection

We report on a new technique for measuring the cathode dark space width and the variation of ground state atomic density within it by measuring the ionization current generated by laser photoiomzation of neutral ground state metallic atoms. The technique is supported by a theoretical model of charge displacement in the dark space. Measurements of dark space width with respect to pressure, current and nature of the buffer gas are presented for an uranium hollow cathode discharge (HCD). Results of variation in density of ground state neutral uranium, in the dark space, versus current and pressure in Xe are also given. These results are of interest when using photoiomzation currents in the HCD dark space for laser spectroscopy, such as photoiomzation studies of refractory elements like uranium.