Strong optical interaction of two adjacent rectangular nanoholes in a gold film

Abstract

The strong near-field optical interaction between two adjacent nanoholes milled in a gold film is investigated. A single nanohole is modeled as a magnetic dipole described by the simple relation between the magnetic- and electric-polarization in electromagnetic theory. To elucidate the role of the electric and magnetic fields in near-field characteristics of a nanohole illuminated by an optical plane-wave, the normalized electric and magnetic power amplitudes are accordingly introduced. This is extended to model the strong optical interaction of the two adjacent nanoholes in the near-field regime, leading to the magnetic coupled-dipole approximation (MCDA). It is shown that the optical transmission spectrum of the nanostructure may exhibit hybridized resonant peaks, depending on the configuration or the polarization. Compared to the known effects in the optical properties of a pair of metal nanoparticles for which the electric-field of the incident light is crucial, here it is illustrated that the magnetic-field of the incident light plays the dominant role in defining the optical properties of the complement structure. Thus, the strength of the interaction of the two adjacent nanoholes and the resulting hybridized plasmon resonances are strongly depends on the magnetic-field orientation in respect to the pair axis as well as on the separating distance of the nanoholes. The theoretical findings are supported by the electromagnetic computations.