The dynamics of the acceleration of ultrathin foil targets by the radiation pressure of superintense, circularly polarized laser pulses is investigated by analytical modeling and particle-in-cell simulations. By addressing self-induced transparency and charge separation effects, it is shown that for "optimal" values of the foil thickness only a thin layer at the rear side is accelerated by radiation pressure. The simple "light sail" model gives a good estimate of the energy per nucleon, but overestimates the conversion efficiency of laser energy into monoenergetic ions.

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Ion acceleration driven by the radiation pressure of circularly polarized pulses is investigated via analytical modeling and particle-in-cell simulations. Both thick and thin targets, i.e. the "hole boring" and "light sail" regimes are considered. Parametric studies in one spatial dimension are used to determine the optimal thickness of thin targets and to address the effects of preformed plasma profiles and laser pulse ellipticity in thick targets. Three-dimensional (3D) simulations show that "flat-top" radial profiles of the intensity are required to prevent early laser pulse breakthrough in thin targets. The 3D simulations are also used to address the issue of the conservation of the angular momentum of the laser pulse and its absorption in the plasma.

The interaction of ultra-high intensity laser pulses with solid targets is studied theoretically and with ParticleIn-Cell (PIC) simulations. The regime of Radiation Pressure Acceleration of ultrathin foil targets is investigated within an improved "Light Sail" or "accelerating mirror" model. The latter provides simple and useful scalings for the characteristics of accelerated ions. The underlying dynamics, unfolded by PIC simulations, is however more complex than the simple model may suggest. An important issue is the heating of electrons that, even if strongly reduced by the use of circulary polarized (CP) pulses, may lead to a significant broadening of the ion spectrum. Radiation Reaction (RR) effects in the ultra-relativistic regime of extreme intensities are included in the PIC simulations via the Landau-Lifshitz formula. Apparently, for linearly polarized pulses RR slightly reduces the ion energy but also contributes to cooling the electrons, while RR effects are rather weak for CP pulses.

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