Efficient Coupling to Plasmonic Multipole Resonances by Using a Multipolar Incident Field

A method to manipulate the multipolar plasmonic response of a nanostructure in the quasi-static limit is introduced. The theoretical method puts on the same footing geometry, dielectric properties, and incident field and proceeds in two steps: it optimizes the geometry of the nanostructure to maximize the intensity of the scattering cross-section spectrum. This is done by calculating the coupling strengths of the different modes of the system to the external field, which the method naturally provides. Then, it exploits the symmetry of the incident electromagnetic field to enhance or suppress specific orders, which, in turn, tunes the field enhancement. We demonstrate the method by using a plasmonic dimer of nanospheres.