  Polarization and radiation reaction (RR) effects in the interaction of a
superintense laser pulse (I > 10^23 W/cm^2) with a thin plasma foil are
investigated with three dimensional particle-in-cell (PIC) simulations. For a
linearly polarized laser pulse, strong anisotropies such as the formation of
two high-energy clumps in the plane perpendicular to the propagation direction
and significant radiation reactions effects are observed. On the contrary,
neither anisotropies nor significant radiation reaction effects are observed
using circularly polarized laser pulses, for which the maximum ion energy
exceeds the value obtained in simulations of lower dimensionality. The
dynamical bending of the initially flat plasma foil leads to the self-formation
of a quasi-parabolic shell that focuses the impinging laser pulse strongly
increasing its energy and momentum densities.
