Generation of ultra-short relativistic-electron-bunch by a laser wakefield

The possibility of the generation of an ultra-short (about one micron long) relativistic (up to a few GeVs) electron-bunch in a moderately nonlinear laser wakefield excited in an underdense plasma by an intense laser pulse is investigated. The ultra-short bunch is formed by trapping, effective compression (both in longitudinal and in transverse directions) and acceleration of an initially nonrelativistic (with kinetic energy of a few hundreds keVs) e-bunch that is injected in front of the laser pulse. The initial bunch may be of poor quality, may have a duration in the order of the laser pulse length or longer and can be generated by a laser-driven photo-cathode RF gun. Our 1D and 3D calculations predict that the accelerated ultra-short bunch will show a low energy spread of less than one percent and a low transverse emittance in the order of a nanometer. An energy gain in the GeV-range is feasible at an accelerating distance of a few centimetres. The total number of accelerated electrons is restricted by the beam loading effect only and can reach a value of 10/sup 8/-10/sup 9/.