Quasimonoenergetic proton bunch generation by dual-peaked electrostatic-field acceleration in foils irradiated by an intense linearly polarized laser.

It is found that stable proton acceleration from a thin foil irradiated by a linearly polarized ultraintense laser can be realized for appropriate foil thickness and laser intensity. A dual-peaked electrostatic field, originating from the oscillating and nonoscillating components of the laser ponderomotive force, is formed around the foil surfaces. This field combines radiation-pressure acceleration and target normal sheath acceleration to produce a single quasimonoenergetic ion bunch. A criterion for this mechanism to be operative is obtained and verified by two-dimensional particle-in-cell simulation. At a laser intensity of ∼5.5×10(22)  W/cm(2), quasimonoenergetic GeV proton bunches are obtained with ∼100  MeV energy spread, less than 4° spatial divergence, and ∼50% energy conversion efficiency from the laser.