Control of laser-accelerated proton beams by modifying the target density with ASE

We demonstrate laser-ion acceleration from a near-critical density plasma, using amplified spontaneous emission (ASE) to convert a solid foil target into a lower-density target. In order to investigate the target density dependence of the laser-ion acceleration, two cases were investigated for which the ASE intensity differed by three orders of magnitude. In the low contrast case the beam centre for higher energy protons is shifted closer to the laser-propagation direction of 45○, while the centre of lower-energy beam remains near the target normal direction. We show that a near-critical density plasma can be used to control proton beam direction based on its energy.