Fig. 1. The light sail concept. The sail is modeled as a perfect mirror of surface density , with the mass density and the thickness. The sail is pushed by a plane wave of intensity and frequency . Notice that the equations of motion for the sail given in (1) and the expression for the mechanical efficiency may be simply obtained by considering the Doppler shift of the reflected radiation [] and the conservation of the ‘number of photons’; see, for example, Ref. [6].

Fig. 2. The first stage of ion acceleration driven by radiation pressure^[18]. The densities of ions () and electrons () are approximated by step-like functions. Ions initially in the layer are accelerated by the charge separation field up to velocity at time .

Fig. 3. 3D particle-in-cell simulations of thin foil acceleration. (a) Space and energy distribution of ions^[25] (reproduced by permission of APS) at from the acceleration start ( laser period). (b) Maximum ion energy versus time^[12] (reproduced by permission of IOP Publishing). Both simulations have been performed for a pulse (FWHM values) with peak amplitude and circular polarization, and a hydrogen plasma foil with surface density , so that . See the references for details.