| In this work we study the effects of Surface Plasmon Resonances (SPR) in the interaction of high power laser pulses with solid targets. The aim is to improve the the absorption efficiency by enhancing and confining the laser field at the solid surface, via excitation of SPR. Since the only feasible way to excite plasmons in these power conditions is via grating coupling, the target surface has to be modulated. Particular care has to be used when shaping the target: its modulation amplitude cannot be too small compared with the laser wavelength, otherwise the laser pre-pulse could infer a disruption in the periodic structured surface, with consequent losses in the interaction with the peak pulse. On the other hand the SPR resonant frequencies may vary with the modulation amplitude, producing distortions in the SPR relation dispersion. In our work, we show that this frequency shift depends quadratically on the modulation amplitude. Then we simulate the dynamics of test electrons in the surface field and we show that a great enhancement of the average electrons kinetic energies occurs when SPR are excited. Thus, the absorption enhancement found in previous works has to be ascribed to the ex- citation of SPR, at whose frequency the structured target behaves like a one dimensional optical cavity. |
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