Ponderomotive snowplow electron acceleration with high energy tilted ultrafast laser pulses

Abstract The application high intensity ultrafast lasers to compact plasma-based electron accelerators has recently been an extremely active area of research. Here, for the first time, we show experimentally and theoretically that carefully sculpting an intense ultrafast pulse in the spatio-temporal domain allows ponderomotive pressure to be used for direct acceleration of electron bunches from rest to relativistic energies. With subluminal group velocity and above-threshold intensity, a laser pulse can capture and accelerate electrons, pushing on them like a snowplow. Acceleration of electrons from rest requires a substantial reduction of group velocity. In this demonstration experiment, we achieve a group velocity of ∼0.6c in a tilted pulse by focusing the output of a novel asymmetric pulse compressor we developed for the petawatt-class ALEPH system at Colorado State University. This direct laser-electron approach opens a route towards exploiting optical spatio-temporal control techniques to sculpt electron beams with desired properties such as narrow energy and angular distributions. The tilted-pulse snowplow technique can be scaled from small-scale to facility-scale amplifiers to produce short electron bunches in the 10 keV−10 MeV range for applications including ultrafast electron diffraction and efficient injection into laser wakefield accelerators for acceleration beyond the GeV level.