Analysis Of Scattering Of Light By Gratings Of Metal-coated Dielectric Nanocylinders

With the rapid development of nanoscience and nanotechnology, the interaction of electromagnetic wave with nanoscale objects remains as an important topic in recent years because of their wide range of applications to the optical sensors, imaging, and integrated devices. The literature on the interaction of light with nanoscale objects in general is of course much broader. The study on the interaction can be organized in many different ways, being dependent on the dimensionality of the objects and the exciting source. In this paper, we shall focus our consideration on the cylindrical structures, which are usually called as nanocylinders or nanowires.The scattering of TE plane wave by single and two metal-coated dielectric nanocylinders has been analyzed by using the cylindrical wave expansion and the T-matrix of a circular cylinder. It was shown that unique near field distributions localized along the nanocylinders are excited when the wavelength of illumination resonates to surface plasmons supported on the inner and outer interfaces of the metal layer. For full understanding of light interaction with nanocylinders, the scattering and absorption cross-sections have also been analyzed as functions of the excited wavelength. It was shown that the spectral responses of the scattering and absorption cross-sections have peaks at the wavelengths near the surface plasmon resonances. For a two nanocylinder system, the strong coupling is attained for a particular wavelength when the separation distance of the cylinders is specified. There exists the plasmon resonant coupling which induces a new plasmon field in the gap region between two cylinders. At the same time, the scattering cross-section is resonantly increased at this wavelength.Light scattering by a grating of the metal(Ag)-coated nanocylinders in the free space, pure metal(Ag) and metal(Ag)-coated nanocylinders supported on the dielectric substrate is investigated using an accurate and rigorous formulation based on the recursive algorithm combined with the lattice sums technique. Special attention is paid to three types of resonances: surface plasmon resonances associated with the metal nanocylinders, Rayleigh anomalies related with the periodic nature of the grating and the resonances due to the coupling between the grating and the dielectric substrate. Near field distribution of the magnetic field, which is parallel to the axis of the nanocylinders, is numerically investigated. Deep physical insight is given to the localization of the field along the interfaces of the metal nanocylinders, formation of the strong reflected field by the grating and the field enhancement at the surface of the dielectric substrate.All these features of the gratings above are technologically important and have wide practical application from the viewpoint of the flexible design and fabrication of the plasmonic optical devices in the future.