Antenna-load Interactions at Optical Frequencies: Impedance Matching to Quantum Systems
Abstract The goal of antenna design at optical frequencies is to deliver optical electromagnetic energy to loads in the form of, e.g., atoms, molecules, or nano-structures, or to enhance the radiativeemission from such structures, or both. A true optical antenna would, on a qualitatively new level, control the light-matter interaction on the nano-scale for controlled optical signal transduction, radiative decay engineering, quantum coherent control, super-resolution microscopy, and provide unprecedented sensitivity in spectroscopy.
However, in contrast to the RF, where exact design rules for antennas, waveguides, and antenna-load matching in terms of their impedances are well established, substantial physical differences limit the simple extension of the RF concepts of antenna design to the optical regime. I will discuss the generalization of the ideal antenna-load interaction at optical frequencies, characterized by far-field transformation from a propagating mode into an antenna resonance, the subsequent transformation of that mode into a nanoscale localization, and the free space transformation via an enhanced local density of states to a quantum load.
These steps define the goal of efficient transformation of incident radiation into a quantum excitation in an impedance matched fashion. I willreview the physical basis of the light-matter interaction at the transitionfrom the rf to optical regime, discuss extension of antenna theory as needed for the design of impedance-matched optical antenna-load coupled systems, and provide several examples of the state of the art in design strategies and suggest future extensions. I will discuss new measurable performance metrics based on electric vector field, measurement, field enhancement, and capture cross section to aid the comparison between different antenna designs.