Multi-MeV electron beam generation by direct laser acceleration in high-density plasma channels

We have measured angularly resolved and absolutely calibrated spectra or th e multi-MeV electrons produced by relativistic self-channeling in a high-de nsity gas jet. Using 200 fs laser pulses with P-L = 1.2 TW, we have investi gated the electron spectrum dependence on the plasma election density in th e range of 3 X 10(19)-4 X 10(20) cm(-3). The experimentally obtained result s are closely reproduced by three-dimensional particle-in-cell simulations. A detailed analysis shows that the self-modulated laser wake field, althou gh active, cannot explain the experimental energy spectrum. The bulk of the fast electrons are produced by direct laser acceleration at the channel be tatron resonance.