When light impinges on a periodically grooved surface, it can be efficiently absorbed and confined in a thin layer as a surface wave. This is the building block of plasmonics and allows guiding and enhancement of electromagnetic fields on a sub-micrometric scale, which is the key to several applications. However, the latter have been limited so far to not very intense light in order to prevent damage of the shallow grating.@
In a recent experiment, by using femtosecond laser pulses short and “clean” enough to prevent early disruption of the grating, researchers have provided evidence of surface wave excitation by a laser pulse so intense that electrons oscillate with relativistic energy. The effect has been observed via an increase of the energy of the emitted protons, which in turn suggests to exploit the mechanism to develop more efficient ultrashort sources of radiation. The observations also call for a theory of nonlinear surface waves in the relativistic regime.@
The experiment was carried out at the SLIC facility of CEA Saclay in France by a collaboration of Italian, French and Czech scientists with the support of the LASERLAB European Network. The collaboration was coordinated by the CNR/INO scientist A. Macchi and has involved several other staff and postdoc scientists from the INO Pisa research unit, including F. Baffigi, L. A. Gizzi, L. Labate, and A. Sgattoni, also in the framework of the CNR ELI-Italy and MIUR FIR-SULDIS projects. Simulations for the experiment were performed on the FERMI supercomputer at CINECA (Bologna) with access provided via an European PRACE project also coordinated by A. Macchi. @
Ref.: T. Ceccotti et al, Evidence of resonant surface wave excitation in the relativistic regime through measurements of proton acceleration from grating targets, Physical Review Letters 111, 185001 (2013)
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