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The interaction of an ultra-short intense laser with an overdense plasma is numerically studied from the point of view of accelerated proton beam generation. We use a one-dimensional particle-in-cell (PIC) code for simplicity. The laser intensity is about 1018  1019 W/cm2, the pulse width is a few tens of fs, and the plasma density is about 4nc  10nc (nc  !2me0/e2). Various forces to accelerate proton ions are investigated as the light intensity and the plasma density are varied . One of the main forces is light pressure, and another is the space-charge-field force induced by rapid electron dispersion. Different behaviors of the energy distribution of the accelerated proton beam are observed under different conditions for the transparency and the opacity of the laser pulse. When the laser light is mostly reflected in front of the plasma slab, the proton ion beams is more collimated by the light pressure. In addition, the kind of polarization of the laser affects the energy spectrum of the accelerated protons, and circular polarization is preferred to linear polarization for effective collimation of an accelerated proton beam.


The interaction of an ultra-short intense laser with an overdense plasma is numerically studied from the point of view of accelerated proton beam generation. We use a one-dimensional particle-in-cell (PIC) code for simplicity. The laser intensity is about 1018  1019 W/cm2, the pulse width is a few tens of fs, and the plasma density is about 4nc  10nc (nc  !2me0/e2). Various forces to accelerate proton ions are investigated as the light intensity and the plasma density are varied . One of the main forces is light pressure, and another is the space-charge-field force induced by rapid electron dispersion. Different behaviors of the energy distribution of the accelerated proton beam are observed under different conditions for the transparency and the opacity of the laser pulse. When the laser light is mostly reflected in front of the plasma slab, the proton ion beams is more collimated by the light pressure. In addition, the kind of polarization of the laser affects the energy spectrum of the accelerated protons, and circular polarization is preferred to linear polarization for effective collimation of an accelerated proton beam.