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The conversion of laser light into soft x rays by irradiation of a high-Z material is theoretically investigated for open, planar geometry. The material may be subdivided into a hot, low-density conversion layer, optically thin for the x rays, and a dense, optically thick reemission zone. The two layers are coupled through radiation only. Dimensional analysis yields asymptotic expressions for the x-ray conversion efficiency and the reemission coefficient and hence for the total converted flux from the target.

The conversion of laser light into soft x rays during interaction of intense laser light with a planar gold target was investigated numerically with the help of the multi code [Comput. Phys. Commun. 49, 475 (1988)]. It solves one-dimensional hydrodynamics including flux-limited electron heat conduction, multigroup radiation diffusion, and steady-state nonlocal thermodynamic equilibrium radiation physics. The influence of various parameters such as the laser intensity, wavelength, and pulse duration on the conversion efficiency of laser light into x rays was studied. Particular emphasis was placed on comparing the numerical results with the model presented in the preceding paper (Part I) [Phys. Fluids B 2, 199 (1990)]. According to this model the radiating plasma can be divided into a conversion layer and a reemission zone. Its essential features are confirmed by the numerical results.

New simple self-similar solutions for the unsteady expansion of a gas into a vacuum are found. They describe supersonic rarefaction in cylindrical and spherical symmetry for an arbitrary adiabatic index. An inner boundary exists at a constant self-similar coordinate. In the asymptotic region a universal isothermal density law is given which depends only on geometry. Important applications lie in the field of laser-generated plasmas.

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The front of an expanding plasma generally exposed to charge separation is shown to acquire asymptotically a speed given by self-similar theory.

A new class of generalized self-similar solutions for the problem of one-dimensional unsteady outflow of a gas into a vacuum is found. It allows a unified and comprehensive description of plane, cylindrical, and spherical symmetric flows for arbitrary polytropic index. A key property is a moving inner boundary. Relative to this, subsonic and supersonic outflows are possible in certain parameter regions. Simple analytic expressions are found near the boundaries and an extensive parameter discussion is presented. The asymptotic solutions are of specific importance. As an application, it is shown that the isothermal corona of a laser-generated plasma is in part described by one of these asymptotic solutions.