Self-injected petawatt laser-driven plasma electron acceleration in 10 17 cm −3 plasma

We report production of a self-injected, collimated (8 mrad divergence), 600 pC bunch of electrons with energies up to 350 MeV from a petawatt laser-driven plasma accelerator in a plasma of electron density n(e) = 10(17)cm(-3), an order of magnitude lower than previous self-injected laser-plasma accelerators. The energy of the focused drive laser pulse (150J, 150 fs) was distributed over several hot spots. Simulations show that these hot spots remained independent over a 5 cm interaction length, and produced weakly nonlinear plasma wakes without bubble formation capable of accelerating pre-heated (similar to 1 MeV) plasma electrons up to the observed energies. The required pre-heating is attributed tentatively to pre-pulse interactions with the plasma.