Resonant Inelastic X-Ray Scattering Studies of a Solid-Density Plasma

Resonant inelastic x-ray scattering (RIXS), while prevalent in atomic and condensed matter physics, has not been used to date in high-energy-density physics research. This can be traced to three important requirements: the x-ray source must be spectrally bright, stable, and have a tunable (narrow-bandwidth) wavelength so as to match the required resonance condition. Such requirements can now be met with the advent of X-Ray FELs such as LCLS. We show how the electronic structure of nickel, heated to form a solid-density plasma at temperatures of tens of eV on femtosecond timescales, can be studied by RIXS using LCLS. [1] We present single-shot measurements of the valence density of states in the x-ray-heated transient system, tuned over a range of incident photon energies, and extract simultaneously electron temperatures, ionization, and ionization potential energies. The RIXS spectrum provides a wealth of information on the valence structure of this solid-density plasma that goes beyond what can be extracted from x-ray absorption or emission spectroscopy alone. \ [1] O.S. Humphries, R.S. Marjoribanks, Q. van den Berg, E.C. Galtier, M.F. Kasim, H.J. Lee, A.J.F. Miscampbell, B. Nagler, R. Royle, J.S. Wark, S.M. Vinko, https://arxiv.org/abs/2001.05