Ultrashort electron bunches from laser-plasma accelerators

Trapping of plasma electrons in the self-modulated laser wakefield accelerator (LWFA) via the coupling of Raman backscatter to the wake is examined analytically and with 3D test particle simulations. The trapping threshold for linear polarization is much less than for circular and occurs well below wavebreaking. Self-channeling provides continuous focusing of the accelerated electrons which, along with relativistic pump laser effects, can enhance 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. Simulations of test electrons in 3D fields indicate the production of relativistic ( : 25 MeV) high-quality electron bunches with ultrashort durations (few fs), small energy spreads (few %), and low normalized emittances (1 mm-mrad).