Electron Acceleration by Relativistic Surface Plasmons in Laser-Grating Interaction

The generation of energetic electron bunches by the interaction of a short, ultraintense (I > 10(19) W/cm(2)) laser pulse with "grating" targets has been investigated in a regime of ultrahigh pulse-to-prepulse contrast (10(12)). For incidence angles close to the resonant condition for surface plasmon excitation, a strong electron emission was observed within a narrow cone along the target surface, with energy spectra peaking at 5-8 MeV and total charge of similar to 100 pC. Both the energy and the number of emitted electrons were strongly enhanced with respect to simple flat targets. The experimental data are closely reproduced by three-dimensional particle-in-cell simulations, which provide evidence for the generation of relativistic surface plasmons and for their role in driving the acceleration process. Besides the possible applications of the scheme as a compact, ultrashort source of MeV electrons, these results are a step forward in the development of high-field plasmonics.