Efficient hybrid-mode excitation in plasmonic nanoantennas by tightly focused vector beams

Efficient optical excitation of hybridized plasmon modes in nanoantennas is vital to achieve many promising functionalities, but it can be challenging due to a field-profile mismatch between the incident light and the hybrid mode. We present a general approach for efficient hybrid-mode excitation by focusing the incident light field in the basis of cylindrically polarized vector beams of various higher-order spiral phases. Such basis vector beams are described in the higher-order polarization states and Stokes parameters (both defined locally in polar coordinates), and visualized correspondingly on the higher-order Poincare spheres. The focal field is formulated exclusively in cylindrical coordinates as a series sum of all focused beams of the associated high-order paraxial beams. Our focal field decomposition enables an analysis of hybrid-mode excitation via higher-order vector beams, and thus yields a straightforward design of an effective mode-matching field profile in the tightly focused region.