Generation of high-amplitude plasma waves for particle acceleration by cross-modulated laser wake fields

A scheme is proposed to amplify the wake field of an ultrashort laser pulse by a second laser pulse co-propagating behind with a duration of a few plasma wavelengths or longer for particle acceleration. It is found that, due to the cross-phase modulation by the wake field, the second laser pulse is modulated quickly and split into a multipulse train, where the durations of subpulses are around a plasma oscillation period. This pulse train amplifies the wake field in turn to a high level until wave breaking. With this scheme, a large-amplitude plasma wave can be generated with laser pulses only at moderate intensities. For example, the effective acceleration field for trapped electrons injected from wave-breaking exceeds 100 GeV/m for incident laser pulses at intensity 3.4×1017 W/cm2 in plasma at one percent of the critical density, as demonstrated by particle-in-cell simulations.