Modeling of a discrete parabolic reflector made of sub-wavelength plasmonic wires

Focusing of waves using solid reflectors is widely used in optics and quasioptics, parabolic reflectors being the most popular and efficient ones. Periodically structured scatterers have been attracting attention of researchers for a long time because of the interesting effects of extraordinary large reflection, transmission and near-field enhancement [1-4]. For the finite periodic gratings of metal scatterers this is explained by effects of surface-plasmon (P) resonances, that are observed on sub-wavelength noble-metal particles and wires in the midinfrared and optical bands [5-7], and grating (G) resonances that are induced by the periodicity [3,4,8]. Excitation of plasmons leads to powerful enhancement of scattered and absorbed light. The wavelengths of the P-resonances depend mainly on the object shape and less on its dimensions. The wavelengths of the Gresonances lie near the Rayleigh wavelengths [9] of linear gratings and hence weakly depend on both the elementary wire shape and its dimension, provided that the wire size is a fraction of the period. In the wave scattering by sparse infinite gratings, G-resonances lead to almost total reflection of the incident field in narrow wavelength bands.