We have used time-resolved x-ray absorption spectroscopy to investigate the unoccupied electronic density of states of warm dense copper, carbon and silicon dioxide that is produced isochorically through the absorption of an ultrafast optical pulse. A motivation for the study of warm dense matter is that such conditions occur in planetary interiors. In copper, the electron temperature can be determined by comparing the measured L3 x-ray absorption edge with simulations. The dynamics of this electron temperature are consistent with a two-temperature model of the electrons and ions. In both amorphous carbon and diamond, an increase in the ï°* resonance results from the lower average coordination number in liquid carbon. In diamond, the structure above the edge disappears rapidly because of the loss of short range order. For SiO2 the O K-edge broadens and a new absorption peak appears at ~9 eV lower photon energy. The peak may be associated with holes created in the valence band. Warm dense copper, carbon and silicon dioxide show a variety of electronic properties through their x-ray absorption spectra.

Electronic Structure of Warm Dense Matter Studied by Ultrafast X-ray Absorption Spectroscopy