Design of Hybrid Nanoantenna-Dielectric-Cavity with Strong Near-Field Intensity Enhancement

This dissertation investigates the Near-Field Intensity Enhancement (NFIE) of plasmonic nano-antennas in the visible and near-infrared frequency region and proposes a gold nanoantenna on a dielectric nanocavity for use in Surface Enhanced Raman Spectroscopy (SERS). Plasmonic nanoantennas allow direct coupling of light to metal and have since gained traction as fabrication methods have become more precise, allowing designs that were previously limited to theories. Attempts have been made to improve the NFIE but most of these efforts have been in improving the nano-antenna design as well as in the use of Fabry-Perot cavities. This dissertation therefore proposes a “hybrid antenna” in the form of a dielectric resonant cavity (DRC) coupled to a plasmonic dipole as a receiver. The interaction that occurs during the coupling is investigated in detail and a relation is made between the overall NFIE and the NFIE introduced by the dielectric resonator modes. A simple way to design dielectric resonator cavities for use at optical frequencies is introduced and data from two commercial electromagnetic field solvers and self-coded FDTD numerical analysis are compared against results found in literature. It is found that the addition of the proposed dielectric resonator nanocavity increases the NFIE of a plasmonic gold dipole by 21 times, from 1750 to 37k. It was further found that the NFIE can be increased further to 68k when mirrored with a gold slab, where other published results not employing optical cavities have a maximum NFIE of 29k. This dissertation contributes by proposing an effective and simple DRC that can significantly improve the near-field properties of surface plasmon resonance to be used in SERS measurements.