  Using ab initio molecular-dynamics simulations combined with linear-response
theory, we studied the x-ray absorption near-edge spectra (XANES) of a
two-temperature dense copper plasma. As the temperature increases, XANES
spectra exhibit a pre-edge structure balanced by a reduction of the absorption
just behind the edge. By performing systematic simulations for various
thermodynamic conditions, we establish a formulation to deduce the electronic
temperature Te directly from the spectral integral of the pre-edge that can be
used for various thermodynamic conditions encountered in a femtosecond heating
experiment where thermal non equilibrium and expanded states have to be
considered.
