The complex problem of a collisionally pumped Ne-like germanium laser is examined through several detailed models. The central model is EHYBRID; a 1 1/2 D fluid code which self consistently treats the plasma expansion with the atomic physics of the Ne-like ion for 124 excited levels through a collisional radiative treatment. The output of EHYBRID is used as data for ray-tracing and saturation codes which generate experimental observables. A detailed description of the models is given. The atomic physics is investigated through a three-level approximation, a steady state collisional radiative treatment and a time-dependent solution within the fluid model. The accurate calculation of the non-steady state ionization balance is identified as a key issue. Time resolved and time integrated output profiles are generated for various experimental configurations, and the effects of saturation and gain narrowing are examined. The agreement with experiment is excellent in virtually every respect.

The agreement between experimental results and theoretical predictions is improved for the temporal dynamics of the gain coefficient on the 3 to 2 transition of the C VI ion at 182 AA. It is shown that nj kinetics improves the description of radiative cleaning of the n=2 level in a partially reabsorbed, expanding plasma, surprisingly increasing the degree of frozen ionization. A detailed description of radiative trapping on the n=2,3 levels is included in the model in the form of the net radiative bracket, calculated through an exact solution of the radiative transfer problem. The accurate treatment of radiative transport is found to convincingly verify the Sobolev formulation of the escape factor.

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There is great interest in the development of XUV lasers with driver energies of a few joules rather than a few kilojoules. One of the most promising ways to accomplish this is based upon the use of fast adiabatic cooling to produce population inversion in recombination to hydrogenic ions(l). Theoretical modelling(2) indicates that the optimum driver for this scheme should produce pulses of duration < 10 ps, ultraviolet wavelength and focusability to sub 10 µm line foci with length of the order 1 cm. Under these conditions saturated laser action at wavelengths below 20 nm is predicted in plasmas created from fibre targets of < 10 µm radius with driver energy < 10 J (see eg Fig 1). Preliminary experimental studies have been carried out using a high brightness 5 J, 10 ps KrF pumped Raman laser beam(3) with observations of fluorescence and possible amplification on the Balmer-α transitions of C VI, O VIII(4). In a current experiment these phenomena are being studied in detail. Our paper will review the theoretical basis for the X-ray laser scheme, describe the experimental and diagnostic system, review previous preliminary results and report on the results of the current more detailed experiment.