  Theoretical study of heavy ion acceleration from ultrathin (<200 nm) gold
foils irradiated by a short pulse laser is presented. Using two dimensional
particle-in-cell simulations the time history of the laser bullet is examined
in order to get insight into the laser energy deposition and ion acceleration
process. For laser pulses with intensity , duration 32 fs, focal spot size 5
mkm and energy 27 Joules the calculated reflection, transmission and coupling
coefficients from a 20 nm foil are 80 %, 5 % and 15 %, respectively. The
conversion efficiency into gold ions is 8 %. Two highly collimated
counter-propagating ion beams have been identified. The forward accelerated
gold ions have average and maximum charge-to-mass ratio of 0.25 and 0.3,
respectively, maximum normalized energy 25 MeV/nucleon and flux . Analytical
model was used to determine a range of foil thicknesses suitable for
acceleration of gold ions in the Radiation Pressure Acceleration regime and the
onset of the Target Normal Sheath Acceleration regime. The numerical
simulations and analytical model point to at least four technical challenges
hindering the heavy ion acceleration: low charge-to-mass ratio, limited number
of ions amenable to acceleration, delayed acceleration and high reflectivity of
the plasma. Finally, a regime suitable for heavy ion acceleration has been
identified in an alternative approach by analyzing the energy absorption and
distribution among participating species and scaling of conversion efficiency,
maximum energy, and flux with laser intensity.
