The formation of a collisional shock wave by the light pressure of a short-laser pulse at intensities in the range of 1018–1023 W/cm2 is considered. In this regime the thermodynamic parameters of the equilibrium states, before and after the shock transition, are related to the relativistic Rankine–Hugoniot equations. The electron and ion temperatures associated with these shock waves are calculated. It is shown that if the time scale of energy dissipation is shorter than the laser pulse duration a collisional shock is formed. The electrons and the ions in the shock-heated layer may have equal or different temperatures, depending on the laser pulse duration, the material density and the laser intensity. This shock wave may serve as a heating mechanism in a fast ignition scheme.

This paper considers the heating of a target in a shock wave created in a planar geometry by the ponderomotive force induced by a short laser pulse with intensity higher than 1018 W/cm2. The shock parameters were calculated using the relativistic Rankine–Hugoniot equations coupled to a laser piston model. The temperatures of the electrons and the ions were calculated as a function of time by using the energy conservation separately for ions and electrons. These equations are supplemented by the ideal gas equations of state (with one or three degrees of freedom) separately for ions and electrons. The efficiency of the transition of the work done by the laser piston into internal thermal energy is calculated in the context of the Hugoniot equations by taking into account the binary collisions during the shock wave formation from the target initial condition to the compressed domain. It is shown that for each laser intensity there is threshold pulse duration for the formation of a shock wave. The explicit calculations are done for an aluminum target.

X rays emitted from Kr clusters illuminated by a femtosecond laser have been observed over a wide spectral region from 3 keV to 15 keV. The measured spectra are characterized by a broad bremsstrahlung continuum and Kα, β lines at 12.66 keV and 14.1 keV. To the best of the authors' knowledge, this is the first observation of Kα, β emission from laser-heated Kr clusters. The bremsstrahlung continuum arising from collisions in the plasma implies a population of hot electrons consistent with a temperature of several kiloelectron volts. The absolute X-ray yield in the 3–15 keV region is found to be of the order of 107 photons per laser pulse. The plasma temperature, estimated from the continuum part of the spectrum as a function of laser intensity and X-ray yield as a function of laser pulse duration, are studied.