Optimization of flat-cone targets for enhanced laser-acceleration of protons

We have analyzed the acceleration of laser-generated protons, produced at the rear surface of flat-cone targets irradiated by anultra-intense (I~5 x 10¹⁹ W/cm²) short (400fs) laser pulse. We used different target sizes and shapes in order to find the optimum target layout. We find that for targets with a too narrow cone structure, the production of the hot electrons, driving the proton acceleration, islocated prior to the accelerating rear surface of the target, resulting in a reduced maximum proton energy.