The wave function of photons in spherical and cylindrical geometries is described by a superposition of electric and magnetic multipoles (dipole, quadrupole, etc.). By efficiently coupling to these multipole orders, antennas form the basis for technologies that transmit and receive radio and microwave frequency electromagnetic radiation. Using metallic nanostructures, researchers have extended antenna concepts to the optical frequency domain, greatly enhancing control over light-matter interactions at the nanoscale. Recently, we have exploited the scattering resonances of high-permittivity particles to realize all-dielectric optical antennas. In this talk, we experimentally and theoretically characterize the resonant modes of dielectric nanowires using Mie theory and infrared spectroscopy. We derive and verify a variety of general analytical results  applicable to all antenna systems and demonstrate novel multipole antenna light emitters (transmitters)  and photo-detectors (receivers) .
Each multipole resonance is characterized by a distinct spatial distribution of electromagnetic radiation. The optical properties of bulk materials arise from the combined response of constituent multipoles. In conventional materials, the electromagnetic response is governed by electric dipole resonances only. By leveraging higher order multipole resonances in dielectric antennas, we access new regimes of optical interactions and demonstrate artificial electromagnetic materials with negative index of refraction . In nanomaterials, we show how inherent structural anisotropies strongly affect macroscopic optical properties. By combining classical antenna calculations with angle, polarization, and energy resolved photoluminescence measurements we quantify optical antenna effects in layered nanomaterials. Specifically, we isolate signatures of intra- and inter-layer excitons by the orientation of their transition dipole moment. We show that Molybdenum Disulfide (MoS2) only supports intra-layer excitons, while the organic semiconductor PTCDA exhibits luminescence from intra- and inter-layer excitons with distinct energies, intensities, and temporal dynamics .
Work sponsored by NSF Center for Probing the Nanoscale, Northrop Grumman, AFOSR MURI, and DOE Energy Frontier Research Center
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