Laser-induced electron trapping in plasma-based accelerators

Trapping of plasma electrons in the self-modulated laser wakefield accelera tor (LWFA) via the coupling of Raman backscatter to the wake is examined an alytically and with three-dimensional (3-D) test particle simulations. The trapping threshold for linear polarization is much less than for circular a nd occurs for wake amplitudes of delta n/n similar to 25%, which is well be low wave breaking. Self-channeling provides continuous focusing of the acce lerated electrons which, along with relativistic pump laser effects, can en hance the energy gain by a factor greater than or equal to 2. The colliding pulse method for injecting electrons in the standard LWFA is examined. Sim ulations of test electrons in 3-D fields indicate the production of relativ istic (greater than or equal to 25 MeV) high-quality electron bunches with ultrashort durations (a few femtoseconds), small energy spreads (a few perc ent), and low normalized emittances (1 mm mrad). (C) 1999 American Institut e of Physics. [S1070-664X(99)96705-8].