OBSERVATION OF ELECTRON ENERGIES BEYOND THE LINEAR DEPHASING LIMIT FROM A LASER-EXCITED RELATIVISTIC PLASMA-WAVE

The spatial extent of the plasma wave and the spectrum of the accelera ted electrons are simultaneously measured when the relativistic plasma wave associated with Raman forward scattering of an intense laser bea m reaches the wave breaking limit. The maximum observed energy of 94 M eV is greater than that expected from the phase slippage between the e lectrons and the accelerating electric field as given by the linear th eory for preinjected electrons. The results are in good agreement with 2D particle-in-cell code simulations of the experiment.