Laser-induced electron trapping in plasma-based 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 for wake amplitudes of 25% which is 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 ≥2. The colliding pulse method for injecting electrons in the standard LWFA is examined. Simulations of test electrons in prescribed 1D fields indicate the production of relativistic (≥25 MeV) electrons with bunch durations as short as 3 fs, energy spreads as small as 0.3%, and densities as high as 1018 cm-3