Angle and polarization dependent coupling of surface plasmon and gap modes in plasmonic gap metasurfaces

Abstract

Plasmonic metasurfaces with coupled gap and collective surface plasmon polariton modes are of interest for a variety of optoelectronic devices. The coupling between the gap and plasmon polariton modes leads to tunable extinction spectra that provide flexibility when used in various photonic applications. We demonstrate both experimentally and numerically the polarization and angle dependent tunable optical extinction spectra of a gold nanoparticles monolayer on a glass substrate in close proximity to a thin aluminum film. The monolayer of gold nanoparticles is separated from the aluminum thin film by a dielectric shellac spacer. We observe three angle and polarization dependent peaks in the extinction spectra when the shellac spacer is 10 nm. The three peaks degenerate into one hybrid mode when the spacer thickness is 30 nm. By using a finite-difference-time-domain (FDTD) numerical method, we confirm the position of both the collective surface plasmon and the gap modes. Changing the polarization of the incident light leads to a change of the width and a shift of the wavelength of the peaks.