Creation of warm, dense Si by rapid heating with intense laser-driven protons and characterization by K-shell absorption spectroscopy

The OMEGA EP short pulse lasers have been used to heat and characterize Si in the Warm Dense Matter (WDM) regime. The primary laser, with 1100J in 10ps produced a proton beam with \textasciitilde 50J of total energy that was focused into a Si wafer face-on 500$\mu $m away, heating it to \textasciitilde 50eV in a timespan of \textless 100ps. The second laser, with 700J in 5ps, irradiated the tip of a Zn wire, producing a bremsstrahlung-like X-ray strobe to backlight the Si at various delays. Absorption measurements show the evolution of Si K-shell features throughout the heating. The Si was initially 0.9 or 1.8$\mu $m thick for adequate absorption, and it was tamped with 1.1$\mu $m CH layers to limit expansion. The expansion has been modeled with the radiation-hydrodynamics code HELIOS, and the X-ray transmission of the expanded target has been modeled with the atomic-radiative code PrismSpect. We present the spectroscopy alongside the modeling and compare the fit conditions to those predicted by LSP particle-in-cell. This proton source could be applied to thicker targets as a way to create uniform, near-solid WDM targets for opacity testing.