Bremsstrahlung and line spectroscopy of warm dense aluminum plasma heated by xuv free-electron-laser radiation

We report the creation of solid-density aluminum plasma using free-electron laser (FEL) radiation at 13.50.3em0exnm wavelength. Ultrashort pulses were focused on a bulk Al target, yielding an intensity of 2×10¹⁴0.3em0exW∕cm². The radiation emitted from the plasma was measured using an xuv spectrometer. Bremsstrahlung and line intensity ratios yield consistent electron temperatures of about 380.3em0exeV, supported by radiation hydrodynamics simulations. This shows that xuv FELs heat up plasmas volumetrically and homogeneously at warm-dense-matter conditions, which are accurately characterized by xuv spectroscopy.