Evidence of Resonant Surface-Wave Excitation in the Relativistic Regime through Measurements of Proton Acceleration from Grating Targets


The interaction of laser pulses with thin grating targets, having a periodic groove at the irradiated surface, was experimentally investigated. Ultrahigh contrast (∼1012) pulses allowed us to demonstrate an enhanced laser-target coupling for the first time in the relativistic regime of ultrahigh intensity >1019  W/cm2. A maximum increase by a factor of 2.5 of the cutoff energy of protons produced by target normal sheath acceleration is observed with respect to plane targets, around the incidence angle expected for the resonant excitation of surface waves. A significant enhancement is also observed for small angles of incidence, out of resonance.


Schematic top view of the experimental setup. The Thomson parabola and the frosted glass screen were located along the target normal direction and the laser specular directions, respectively.