Focusing of short-pulse high-intensity laser-accelerated proton beams

Recent progress in generating high-energy (>50 MeV) protons from intense laser–matter interactions (1018–1021Wcm2; refs 1–7) has opened up new areas of research, with applications in radiography8, oncology9, astrophysics10, medical imaging11, high-energy-density physics12–14, and ion-proton beam fast ignition15–19. With the discovery of proton focusing with curved surfaces20,21, rapid advances in these areas will be driven by improved focusing technologies. Here we report on the first investigation of the generation and focusing of a proton beam using a cone-shaped target.We clearly show that the focusing is strongly affected by the electric fields in the beam in both open and enclosed (cone) geometries, bending the trajectories near the axis. Also in the cone geometry, a sheath electric field effectively ‘channels’ the proton beam through the cone tip, substantially improving the beam focusing properties. These results agree well with particle simulations and provide the physics basis for many future applications.