Generation of relativistic electrons via interaction between ultra-short laser pulse and supersonic gas jet

We have studied generation of relativistic electrons by interaction between a high intensity ultra-short laser pulse (Ti:Sapphire, 12 TW, 50 fs, lambda=790 nm) and gas jet. In the experiment, spatial and energy distribution of energetic electrons produced by an ultra-short, intense laser pulse in a He gas jet are measured. They depend strongly on the contrast ratio and shape of the laser prepulse. In the case of a proper prepulse the electrons are injected at the shock front produced by the prepulse and accelerated by consequent plasma wake-field up to tens MeV forming a narrow-coned ejection angle. In the case of non-monotonic prepulse, hydrodynamic instability leads to a broader, spotted spatial distribution. The numerical analysis based on a 2D hydrodynamics (for the laser prepulse) and 2D particle-in-cell simulation justify the mechanism of electron injection and acceleration.