Abstract
We have measured angularly resolved and absolutely calibrated spectra of the multi-MeV electrons produced by relativistic self-channeling in a high-density gas jet. Using 200 fs laser pulses with ${P}_{L}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.2\mathrm{TW}$, we have investigated the electron spectrum dependence on the plasma electron density in the range of $3\ifmmode\times\else\texttimes\fi{}{10}^{19}--4\ifmmode\times\else\texttimes\fi{}{10}^{20}{\mathrm{cm}}^{\ensuremath{-}3}$. The experimentally obtained results are closely reproduced by three-dimensional particle-in-cell simulations. A detailed analysis shows that the self-modulated laser wake field, although active, cannot explain the experimental energy spectrum. The bulk of the fast electrons are produced by direct laser acceleration at the channel betatron resonance.
Published Version
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