Nonlinear optics in relativistic plasmas and laser wake field 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 10⁹ total electrons, with an energy distribution maximizing at 2 megaelectron volts, a transverse emitrance as low as 1 millimeter- milliradian, and a field gradient of up to 2 megaelectron volts per centimeter). Electron acceleration and the appearance of high-frequency modulations in the transmitted light spectrum were 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.