Laser-Driven Shock Acceleration of Ion Beams from Spherical Mass-Limited Targets

Abstract

We report on experimental studies of ion acceleration from spherical targets of diameter $15\mu \mathrm{m}$ irradiated by ultraintense ($1\times {10}^{20}\mathrm{W}/{\mathrm{cm}}^2$) pulses from a 20-TW Ti:sapphire laser system. A highly directed proton beam with plateau-shaped spectrum extending to energies up to 8 MeV is observed in the laser propagation direction. This beam arises from acceleration in a converging shock launched by the laser, which is confirmed by 3-dimensional particle-in-cell simulations. The temporal evolution of the shock-front curvature shows excellent agreement with a two-dimensional radiation pressure model.