Theoretical model for optical properties of symmetric trimer nanoholes in a gold film

Abstract

In this study, optical properties of a symmetric nanohole trimer milled in a gold film are studied using theoretical calculations and numerical simulations. The theoretical model is based on a closed-form relation of the electric and magnetic polarizabilities of a circular nanohole. By modeling each nanohole as a magnetic point-dipole and extending the symmetry-adapted linear combination to the in-plane nanoholes, the mutual effects of the nanoholes on the scattering spectrum are demonstrated. The numerical approach is based on the finite-difference time-domain method, and the numerical results support the theoretical approach. The results indicate that two distinct resonant peaks can be seen in the scattering spectrum of the nanohole trimer, which are due to antibonding and bonding plasmon resonant modes, respectively. The magnetic fields and the corresponding magnetic point-dipoles of the lower nanoholes are in-phase and out-of-phase of the perpendicular and parallel magnetic field components of the incident field, respectively. The upper nanohole at the antibonding resonant wavelength has a phase difference of approximately 30° with the lower nanoholes.