21 May 2013 Resonance effects in the optical antennas shaped as finite comb-like gratings of noble-metal nanostrips
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Active research into nanoscience and nanotechnologies that are available for nano fabrication have lead to considerable progress in the understanding of the optical properties of metals on nanometer scale. Here, noble-metal strip-like nanostructures are attractive objects of research. Indeed, they can be easily manufactured and serve as building blocks of optical nanoantennas and sensors with unique geometry-dependent optical properties. This is because they display intensive localized surface-plasmon resonances in the visible and far-infrared ranges that lead to near- and far-field enhancement effects. Thanks to surface-plasmon resonances, multi-element finite gratings have attractive properties of extraordinarily large reflection, absorption, and transmission, depending on the arrangement of the elementary cell of the grating. All these phenomena are greatly influenced by the so-called grating resonances which appear due to periodicity. The 2D modeling of electromagnetic wave scattering by thin noble-metal nanosize strips and their finite-periodical ensembles arranged in comb-like gratings is considered. Our analysis is carried out using new efficient, convergent and accurate method. It is based, first, on the use of the generalized boundary conditions (GBC) valid for a thin and highcontrast material layer; they allow us to consider only the limit values of the field components and reduce integration contour to the collection of corresponding strip median lines. Second, for the building of discrete model of the obtained singular integral equations, we use very efficient Nystrom-type algorithm with quadrature formulas of interpolation type. We study the SPRs of the finite periodic comb-like strip ensembles versus the incidence angle of the plane electromagnetic wave and the strip characteristics; both near-field and far-field properties of the associated surfaceplasmon resonances and especially local field enhancements or focusing effects are analyzed. Moreover, we investigate the periodicity-induced properties such as the grating resonances in the context of the development of optimal design strategies for efficient multi-strip optical nanoantennas
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Olga V. Shapoval, Alexander I. Nosich, Jiří Čtyroký, "Resonance effects in the optical antennas shaped as finite comb-like gratings of noble-metal nanostrips", Proc. SPIE 8781, Integrated Optics: Physics and Simulations, 87810U (21 May 2013); doi: 10.1117/12.2018854; https://doi.org/10.1117/12.2018854

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