Nonlinear Optics in Relativistic Plasmas and Laser Wakefield Acceleration of Electrons

When a terawatt-peak-power laser beam is focused into a gas jet, an electron plasma wave, driven by forward Raman scattering, is observed to accelerate a naturally collimated beam of electrons to relativistic energies (up to 10 9 total electrons, with an energy distribution maximizing at 2 MeV, a transverse emittance as low as 1 mm-mrad and a field gradient of up to 2 GeV/cm). Electron acceleration and the appearance of high-frequency modulations in the transmitted light spectrum are both found to have sharp thresholds in laser power and plasma density. A hole in the center of the electron beam may indicate that plasma electrons were expelled radially