Enhanced laser ion acceleration from mass-limited foils

We have performed an analysis of ultra-intense laser interaction with solid mass-limited targets (MLT) via electrodynamic 2D3V particle-in-cell simulations. The interaction with long (300 fs) high intensity (1020W/cm2) laser pulses with targets of diameter down to 1 micron is described in detail with respect to electron dynamics and proton and ion acceleration. Depending on the foil diameter, different effects consecutively arise. Electrons laterally recirculate within the target, smoothening the target rear accelerating sheath and increasing the hot electron density and temperature. We developed an analytical model which enables us to predict the electron energy distribution of an MLT. Our results suggest that the most significant ion energy enhancement should be expected for MLT with diameter below the laser focal spot size. The spread of energetic protons is decreased for medium sized foils while it is greatly increased for foils of size near the focal spot size.