Direct excitation of dark plasmonic resonances under visible light at normal incidence.

Dark plasmon resonance modes are optical modes that have small scattering cross-sections and are thus difficult to excite directly by light at normal incidence. In this paper, we propose to excite quadrupolar and higher-order modes with normal incident light (in the visible regime) on a continuous plasmonic metallic surface covering a dielectric pillar array, hence resulting in narrow-band perfect absorption. Different from the general electromagnetic means of inducing dark modes, our dark modes are due to charge densities that are electrically induced by the standing-wave resonance of current on the thin metal sidewall of pillars. This new means of exciting dark modes can significantly improve the excitation efficiency and also provides an easy way to excite strong higher-order modes.