Ion explosion and multi-mega-electron-volt ion generation from an underdense plasma layer irradiated by a relativistically intense short-pulse laser

Ion acceleration and expansion in the interaction of a relativistically int ense short-pulse laser with an underdense plasma layer are investigated. Io n and electron dynamics are studied by a two-dimensional particle-in-cell s imulation with the real mass ratio. It is shown that the longitudinal elect ric field induced by electron evacuation due to a large ponderomotive force or light pressure can accelerate ions to several MeV in the direction of t he laser propagation. It is after the laser completely passes through the p lasma layer that the, ion explosion starts to be significant. [S1063-651X(9 9)04611-5].