Effective model and investigation of the near-field enhancement and subwavelength imaging properties of multilayer arrays of plasmonic nanospheres.

When a small radiating or scattering object is placed near a multilayer array of plasmonic nanospheres, on the other side the optical near field is enhanced due to the excitation of resonant modes in the layers. For some particular frequencies, the field behind the array is concentrated in a subwavelength region, creating a super resolution effect. Resonating layers are able to reproduce (transport) part of the evanescent spectrum to the other side of these layers which otherwise would decay rapidly. We explore the mechanism of evanescent field transport and subwavelength field concentration on the other side of the layered material and show the relationship between near-field enhancement, field concentration, and modal dispersion characteristics. A detailed investigation of these phenomena is carried out by using an effective numerical model based on the array scanning method (ASM) combined with the Ewald method to accelerate the convergence of the dyadic Green function calculation. The subwavelength-sized spheres forming the arrays are represented as single dipole radiators, and the model of their interactions takes into account all the radiative and reactive field components.