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Abstract
The recombination approach for development of a short wavelength laser is one of two schemes used in recent demonstrations of high gain in the soft X-ray region. In this work, a theoretical and experimental study of recombination pumped soft X-ray population inversions in Li-like carbon (CIV) and H-like carbon (CVI) in CO(,2) laser produced plasmas is presented. A collisional radiative model is used to examine the behavior of the gain coefficients for various transitions in the C('5+) ion with plasma parameters, and the optimum conditions for gain defined. A general formalism that elucidates the separate roles of radiative power loss and electron cooling in dense transient plasmas is described and used to examine the feasibility of quickly radiatively cooling a dense plasma to bring about optimum conditions for gain in a recombination system. Experimental studies of the effectiveness of radiation cooling in generating recombination pumped soft X-ray population inversions in CIV are carried out in freely expanding CO(,2) laser produced plasmas. Measurements of gain length products as high as 6.5 on the 182 (ANGSTROM) transition in CVI in magnetically confined CO(,2) laser produced plasmas are reviewed and observations of stimulated emission at 182 (ANGSTROM) obtained with an XUV multilayer mirror in use are presented. In both of these experiments, radiation cooling is shown to play a significant role in bringing about the conditions necessary for gain. In addition to this work, results from a preliminary test of a resonant photoexcitation experiment involving AIV pumping FVI are presented.
