Modified Fresnel Zone Plate—An Example for Systematic Excitation of Subradiant Modes of a Plasmonic Structure

Subradiant modes can exhibit sharper spectral response, and lower radiative loss compared to the super-radiant modes of plasmonic nanostructures. Selective excitation of these modes is challenging, and has practical importance. In this paper, a systematic procedure for determining, and individually exciting the subradiant modes of a plasmonic nanostructure is presented by utilizing our previously reported T-matrix formulation. As an example, we calculate various modes of a gold nanodimer, and determine the incident field required for exciting a subradiant mode of this nanostructure. This field is then generated by a modified zone plate lens. The expansion of scattered field, as well as the scattering power spectrum confirms the excitation of the subradiant mode. The total field is compared with those obtained using the finite-difference time domain method and method of moments.