  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.
