Laser Heating of Solid Matter by Light-Pressure-Driven Shocks at Ultrarelativistic Intensities

Abstract

The heating of solid targets irradiated by $5\times {10}^{20}\mathrm{W}{\mathrm{cm}}^{-2}$, 0.8 ps, $1.05\mu \mathrm{m}$ wavelength laser light is studied by x-ray spectroscopy of the $K$-shell emission from thin layers of Ni, Mo, and V. A surface layer is heated to $\sim 5\mathrm{keV}$ with an axial temperature gradient of $0.6\mu \mathrm{m}$ scale length. Images of Ni ${\mathrm{Ly}}_{\alpha }$ show the hot region has $\le 25\mu \mathrm{m}$ diameter. These data are consistent with collisional particle-in-cell simulations using preformed plasma density profiles from hydrodynamic modeling which show that the $>100\mathrm{G}\mathrm{bar}$ light pressure compresses the preformed plasma and drives a shock into the solid, heating a thin layer.