  The interaction of ultrashort, high intensity laser pulses with thin foil
targets leads to ion acceleration on the target rear surface. To make this ion
source useful for applications, it is important to optimize the transfer of
energy from the laser into the accelerated ions. One of the most promising ways
to achieve this consists in engineering the target front by introducing
periodic nanostructures.
  In this paper, the effect of these structures on ion acceleration is studied
analytically and with multi-dimensional particle-in-cell simulations. We
assessed the role of the structure shape, size, and the angle of laser
incidence for obtaining the efficient energy transfer. Local control of
electron trajectories is exploited to maximise the energy delivered into the
target. Based on our numerical simulations, we propose a precise range of
parameters for fabrication of nanostructured targets, which can increase the
energy of the accelerated ions without requiring a higher laser intensity.
