Generation of highly collimated high-current ion beams by skin-layer laser-plasma interaction at relativistic laser intensities

Generation of fast ion beams by laser-induced skin-layer ponderomotive acceleration has been studied using a two-dimensional (2D) two-fluid relativistic computer code. It is shown that the key parameter determining the spatial structure and angular divergence of the ion beam is the ratio dL∕Ln, where dL is the laser beam diameter and Ln is the plasma density gradient scale length. When dL⪢Ln, a dense highly collimated megaampere ion (proton) beam of the ion current density approaching TA∕cm2 can be generated by skin-layer ponderomotive acceleration, even with a tabletop subpicosecond laser.