Electron-yield enhancement in a laser-wakefield accelerator driven by asymmetric laser pulses.

The effect of asymmetric laser pulses on electron yield from a laser wakefield accelerator has been experimentally studied using >10(19) cm(-3) plasmas and a 10 TW, >45 fs, Ti:Al2O3 laser. The laser pulse shape was controlled through nonlinear chirp with a grating pair compressor. Pulses (76 fs FWHM) with a steep rise and positive chirp were found to significantly enhance the electron yield compared to pulses with a gentle rise and negative chirp. Theory and simulation show that fast rising pulses can generate larger amplitude wakes that seed the growth of the self-modulation instability, and that frequency chirp is of minimal importance for the experimental parameters.