Focusing of picosecond laser pulses in cone geometries*

Short-pulse laser applications like K-alpha based X-ray backlighters, or the fast-ignition approach to inertial confinement fusion require relativistic laser intensities $>$1019W/cm$^2$ over relatively small spots, i.e., radius $\sim$10$\mu$m, while high power laser systems will deliver most of their energy in $\sim$200$\mu$m spots. We study the focusing of picosecond-scale laser pulses in converging target geometries over an intensity range 1017-1020W/cm$^2$ using particle-in-cell simulations, paying special attention at the interaction of intense light with the cone walls.