Laser heating of solid matter by light-pressure-driven shocks at ultrarelativistic intensities

The heating of solid targets irradiated by 5x10(20) W cm(-2), 0.8 ps, 1.05 mu 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 similar to 5 keV with an axial temperature gradient of 0.6 mu m scale length. Images of Ni Ly(alpha) show the hot region has <= 25 mu 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 G bar light pressure compresses the preformed plasma and drives a shock into the solid, heating a thin layer.