Characterization of electron beams produced by ultrashort (30 fs) laser pulses

Detailed measurements of electron spectra and charges from the interaction of 10 Hz, 600 mJ laser pulses in the relativistic regime with a gas jet have been done over a wide range of intensities (10(18)-2x10(19) W/cm(2)) and electron densities (1.5x10(18)-1.5x10(20) cm(-3)), from the "classical laser wakefield regime" to the "self-modulated laser wakefield" regime. In the best case the maximum electron energy reaches 70 MeV. It increases at lower electron densities and higher laser intensities. A total charge of 8 nC was measured. The presented simulation results indicate that the electrons are accelerated mainly by relativistic plasma waves, and, to some extent, by direct laser acceleration. (C) 2001 American Institute of Physics.