GeV mono-energetic proton beam generation in laser foil-plasma interactions

When an intense Gaussian laser pulse (I > 10²¹ W/cm²) with circular polarization (CP) is incident on a planar thin foil, the foil is curved and is transformed into a "cocoon". Rayleigh-Taylor like instabilities develop much more slowly as the radiation pressure is increased, so that these instabilities can disperse nearly the whole cocoon into low density plasma cloud and only a clump (with a size about 1~2lambda) is left in the center of the target. As long as the laser gradually penetrates into the plasma cloud, the photon cavity can be formed and the laser pulse begins to embrace the clump. As the central clump is focused and pushed by the photon cavity (the three-dimensional beam compression), a monoenergetic and highly collimated proton beam is realized. As the photon cavity is helpful to realize the stable acceleration of GeV proton beams with a very low energy spread, so that nearly GeV monoenergetic and collimated proton beam can be generated, which is identified by 2D and 3D particle-in-cell (PIC) simulations.