Excitation of Giant Surface Waves During Laser Wake Field Acceleration
We have detected the presence of very high intensity surface waves that are excited during plasma waveguided laser wakefield acceleration. Wakefield acceleration can be enchanced by the introduction of an ``all optical" plasma waveguide that confines and guides a laser pulse at the optimal intensity over long distances, producing quasimonoenergetic multi-GeV electron bunches. However strong pulses of radio frequency radiation (RF) are also produced, and particle in cell simulations show why: a continuous stream of multi-MeV electrons are also ejected radially from the plasma due to nonlinear wave breaking, and these excite and copropagate coherently with a giant cylindrical Sommerfeld surface wave. Laboratory measurements, simulations, and analytic approximations all converge on a 20 J laser pulse exciting a 1 Joule, 400 GW broadband THz surface wave, with a peak electric field strength of 35 GV/m.