Optical Antennas as Nanocavities: Super-Resolution Mapping of the Vectorial EM Field and Coupling Strength

Optical (nano)antennas reversibly and efficiently convert free propagating optical radiation into localized energy. Nanoantennas confine light at sub-wavelength volumes, and thus produce huge local field enhancement. As a result optical antennas are increasingly applied in a wide variety of applications such as super-resolution microscopy, Raman scattering, bio-sensing, and local nonlinear processes to name a few. At the level of single photon emitters, nanoantennas are extensively used as a tool to increase the excitation rate and modify emission properties.

Such confined nanovolumes of light at the antenna have non-zero field components in all directions (x, y, and z). This vectorial field has a strong position and orientation dependence and requires full nanoscale characterization. We demonstrate a technique to measure the vectorial mode map of a resonant dipole antenna with deterministic position control of single molecules. Furthermore, we treat antennas as nanocavities and investigate their applicability for cavity QED. In this work, we show that by positioning of a single molecule with nanometer accuracy inside the mode volume of a nanoantenna, we maximize the coupling to the antenna and achieve coupling rates that are much higher than optical microcavities. This makes such systems highly efficient true single-photon sources with a photon emission rate above 1 GHz.

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