Towards Laser Ion Acceleration With Holed Targets

Although the interaction of a flat-foil with currently available laser intensities is now considered a routine process, during the last decade emphasis is given to targets with complex geometries aiming on increasing the ion energy. This work presents a target geometry where two symmetric side-holes and a central-hole are drilled into the foil. A study of the various side-holes and central-hole length combinations is performed with 2-dimensional particle-in-cell simulations for polyethylene targets and a laser intensity of 5.2x10^21 W cm^-2. The holed-targets show a remarkable increase of the conversion efficiency, which corresponds to a different target configuration for electrons, protons and carbon ions. Furthermore, diffraction of the laser pulse leads to a directional high energy electron beam, with a temperature of ~40 MeV or seven times higher than in the case of a flat-foil. The higher conversion efficiency consequently leads to a significant enhancement of the maximum proton energy from holed-targets.