Electron acceleration in Nd-laser plasma beat-wave experiments

The beating between two colinear Nd-YLF (λ = 1.053 μm, τ = 90 ps) and Nd-YAG (λ = 1.064 μm, τ = 160 ps) lasers in a homogeneous plasma (n_e = 10¹⁷cm^-3) generates intense relativistic plasma waves associated with a high longitudinal electric field of the order of 1 GVm^-1. In the conditions of the experiment, these electron plasma waves couple with ion waves in the regime of modulational instability as it has been demonstrated by electric field amplitude and saturation time measurements by Thomson scattering. When 3 MeV energy electrons are injected into the plasma, several hundreds of electrons accelerated up to 3.7 MeV are observed in correlation with the Thomson scattering signal associated to the plasma waves. This result is in agreement with a numerical simulation which takes into account the relative focussing geometry of electron and laser beams.