Design of X-UV multilayers for high X-ray flux

Many promising applications for multilayer X-ray optical elements — X-ray laser cavities, plasma diagnostics, synchrotron optics, etc. — subject them to intense X radiation. This paper discusses the initial attempts at understanding the physical processes that are likely to degrade the performance of multilayer X-ray mirrors, the selection of optimal pairs of materials to resist heat damage, methods — including simple analytic, semianalytic models and hydrodynamic code simulations — of estimating multilayer performance under extreme heat loading, and finally experimental data is presented, discussed, analyzed and compared with predictions. For example W/C, V/C, and WC/C multilayers subjected to X-ray fluxes on the order of 150 MW cm-2 using laser generated plasma maintain near peak reflectivity for at least 1 ns, but are eventually destroyed. Considerably more theoretical and experimental study at higher incident fluxes will be required before our understanding is sufficient to routinely design optimal multilayer mirrors for a particular high flux application. It also appears that the experimental techniques developed in the study of robust multilayers may be useful for the investigation of processes important in materials.