Optimal Design of Focusing Nanoantennas for Light

Optical antennas work similar to antennas for the radio-frequency regime and convert electromagnetic radiation into oscillating electrical currents. Charge density accumulations form at the antenna surface leading to strong and localized near-fields. Since most optical antennas have dimensions of a few hundred nanometers, their near-fields allow the focusing of electromagnetic fields to volumes much smaller than the diffraction limit, with intensities several orders of magnitude larger than achievable with classical diffractive and refractive optical elements. In this work the optimization of focusing optical antennas is based on an approach that is a lively research field and has often proved successful for radio-frequency-antennas: evolutionary algorithms. Within this work, new and unexpected antenna geometries have been developed, tested in experiment and described with a novel theoretic framework within the classical Maxwell Equations. These results, which resemble a 3D-modematching principle, will ease the design of novel optical antennas for any given application.