Observation of radiative burnthrough in x-ray heated beryllium by time-resolved spectroscopy

Abstract

A 0.5-\ensuremath{\mu}m-thick beryllium foil is heated by thermal x rays from a laser-irradiated converter foil up to temperatures of a few 10 eV. During the transformation of the solid Be into an ionized gas time-resolved absorption spectra have been measured in the region 100 eV \ensuremath{\lesssim}h\ensuremath{\nu}\ensuremath{\lesssim}250 eV. The measurements agree well with calculations of the radiation transport, for which electron-impact line broadening was found to be essential. Smoothing of the Be K edge observed in the beginning of the heating, when the foil is still in a partially degenerate state, is attributed to thermal smoothing of the Fermi edge.