A COMPUTATIONAL INVESTIGATION OF THE NEON-LIKE GERMANIUM COLLISIONALLY PUMPED LASER

The complex problem of a collisionally pumped Ne-like geranium laser i s examined through several detailed models. The central model is EHYBR ID; a 1 1/2D fluid code which self consistently treats the plasma expa nsion with the atomic physics of the Ne-like ion for 124 excited level s through a collisional radiative treatment. The output of EHYBRID is used as data for ray-tracing and saturation codes which generate exper imental observables. A detailed description of the models is given. Th e atomic physics is investigated through a three-level approximation, a steady state collisional radiative treatment and a time-dependent so lution within the fluid model. The accurate calculation of the non-ste ady state ionization balance is identified as a key issue. Time resolv ed and time integrated output profiles are generated for various exper imental configurations, and the effects of saturation and pin narrowin g are examined. The agreement with experiment is excellent in virtuall y every respect. The principal anomaly which we cannot definitely acco unt for is the high predicted gain on the 196 angstrom J = 0 --> 1 tra nsition. The magnitudes of gain and the deflected angle suffered by th e output beam as calculated by 2D ray-tracing are both too large. Howe ver, a 3D ray-tracing treatment which includes the effects of transver se refraction totally resolves the latter of these difficulties and pa rtially resolves the former. The slightly high gain coefficient (appro ximately 30% with 3D ray-tracing) and the slightly low beam divergence are the only difficulties at present, although plasma inhomogeneities am likely to be responsible for these small discrepancies. All other quantities we have examined, such as those associated with the atomic physics, output beam characteristics and saturation are very well repr oduced.