Electron acceleration in the moderately underdense plasmas

The production of high-energy electron beams has been investigated by using a 1.8-TW, 100-fs laser pulse in the moderately underdense plasma of n(e)/n(c) greater than or equal to0.1. The self-channeling was terminated by the filament structure at the length of around I mm, even if the large uniform density gas-target was used. The emission of MeV-electron beams correlated with the abrupt transition of the propagation mode from the self-channeling to the filament structure. The experimental results such as the power-law energy spectrum of E-3.5 reaching the maximum energy of 2 MeV and the divergence angle of 6-8degrees were well explained by the stochastic direct laser acceleration model based on the random phase jump taking account of the focusing effect by the self-generated magnetic field.