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 $T_e$ 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 nonequilibrium and expanded states have to be considered.

• Received 18 March 2019
• Revised 13 February 2020
• Accepted 27 February 2020

DOI:https://doi.org/10.1103/PhysRevB.101.125127