Proton and ion acceleration by an ultra-shortpulse sub Peta-watt laser in deformed double-layer thin foils

Proton and ion acceleration by sub Peta-watt laser radiation in overdense plasmas, especially for convex thin foils, is studied by 2D3V-PIC (Particle in Cell) numerical simulations. It is found that the target and pulse shape design is important for the acceleration of the charged particles. When a superintense laser pulse interacts with a thin slab of ablative overdense plasma formed by the pre-pulse of the laser, its pondermotive pressure blows all the electrons away from a finite diameter spot on the slab. Consequently, the absorption efficiency of the laser is larger than 50%, but ion acceleration efficiency is small in the case of the material composed of atoms of large mass number, for example, Al. When the surface of the target is coated with a rigid solid or clusters, ions are accelerated efficiently and gain energies as high as 100 MeV. If hydrogen is coated on the back of the thin Al foil, due to the Coulomb explosion of ions, protons are accelerated more efficiently than the hydrogen foil.