Proton acceleration from picosecond-laser interaction with a hydrocarbon target

As an intense picosecond laser pulse irradiates a hydrocarbon target, the protons therein can be accelerated by the radiation pressure as well as the sheath field behind the target. We investigate the effect of the laser and hydrocarbon target parameters on proton acceleration with two/three-dimensional particle-in-cell simulations. It is found that the resulting two-ion species plasma can generate a multiple peaked charge-separation field that accelerates the protons. In particular, a smaller carbon-to-hydrogen ratio, as well as the thinner and/or lower density of the target, leads to a larger sheath field and thus proton beams with a larger cutoff energy and smoother energy spectrum. These results may be useful in achieving high-flux quasi-monoenergetic proton beams by properly designing the hydrocarbon target.