Characterization of the ultrafast x-ray heating of iron foils*

We present experimental data showing the thermodynamic response of metal foils to intense x-ray irradiation. Thin (300 nm) iron foils were irradiated with up to 3 mJ of x-rays in a 9 keV, 40 fs free electron laser pulse generated by the Linac Coherent Light Source, Stanford University. The x-rays heat the foil uniformly, depositing several keV/atom to create a hot-dense state. We observed the non-collective x-ray scattering from the laser pulse, obtaining wavelength-resolved spectra that are sensitive to the temperature and charge distribution in the sample. The values inferred from the x-ray scattering are compared to predictions from atomic kinetics simulations as well as time-integrated measurements of the temperature from the soft x-ray bremsstrahlung emission.