Generation of a ring-focus by the use of a deformable mirror

The target-normal-sheath-acceleration (TNSA) is a very promising way to accelerate protons by relativistic laser-plasma interaction. A central issue is still to increase the energy of the accelerated protons and to reduce their divergence. Therefore one approach is to vary the intensity distribution of the incoming laser-beam and by that the electron sheath on the rear-side which accelerates the protons. A ring-shaped intensity distribution promises an improvement for both features, so a deeper understanding how to generate and control such a distribution is required. The use of a deformable mirror is one method to shape the focal intensity distribution of an intense laser-beam in such a way. In order to get the desired intensity distribution in the focal plane it is necessary to do numerical simulations to get the appropriated shape of the deformable mirror. The mirror itself comes up with some constraints which must be taken into account as well and require a special adjustment. The results of the simulations and whether the theoretical results are technically feasible will be presented. The experimental investigations using a copropagating alignment beam and a closed loop adaptive optics were performed at the Draco Laser facility of the Helmholtz-Zentrum Dresden-Rossendorf.