Surface Plasmon Nanostructures Some Optical Properties Of Research

Surface plasmon polaritons (SPPs) have been proved to better powerful tool for theoptical manipulation on nanoscale. The nanoparticle on the metal thin film plays animportant role of surface plasmon polaritons. If the metallic nanoparticles are designed withsuitable shape, size and arrangement, electric field magnitude can be highly improved.Further, excitation, focusing and directing of surface plasmon polaritons with nanoparticleslocated on a finite metal layer could be accomplished theoretically.No matter which method is used for the calculation of scattered fields, there will be acommon difficulty: the evaluation of Sommerfeld integrals, which is extremely timeconsuming. The integration along steepest descent paths is introduced to evaluate theseSommerfeld integrals. Numerical results show that the fast method can greatly acceleratethe computation for scattering problems. Based on the fast evaluation of Sommerfeldintegrals, the radiation of an arbitrarily oriented electric dipole in a half space is firstanalyzed and computed.Excitation, focusing and directing of surface plasmon polaritons with curved chains ofnanoparticles located on a finite gold layer are investigated theoretically. The theory ofGreen’s dyadic functions on a layered reference system is outlined and electromagneticproperties of surface plasmons are discussed. A curved chain of nanoparticles in upperhalf-space is divided into a number of cubic cells and the integral equation is reduced to amatrix equation using coupled dipole formalism. Then we calculate the electric fields at anypoint on gold surface.Numerical simulations of the configuration investigated experimentally are carried outbased on the Green’s tensor formalism and dipole approximation. We demonstrate that, byusing a relatively narrow Gaussian beam (at normal incidence) interacting only with aportion of a curved chain of nanoparticles, one can excite an SPP beam whose divergenceand propagation direction are dictated by the incident light spot size and its position alongthe chain. It is also found that the SPPs focusing regime is strongly influenced by the chaininter-particle distance. Comparison of numerical results with experimental data shows goodagreement with respect to the observed features in SPPs focusing and directing, providingthe guidelines for a proper choice of the system parameters.