Theory and Simulation Techniques of Broadband Light-Matter Interactions in Nanophotonics

Abstract

The field of nanophotonics has grown rapidly over the past few decades, resulting in new optical technologies that affect nearly every aspect of our day-to-day lives, from biomedical sensing and drug delivery to telecommunication to quantum electrodynamics for information processing. With the emergence of a new generation of photonic and plasmonic hybrid structures, the need for more efficient and sophisticated theoretical and numerical tools and techniques has become essential for both exploring fundamental optical physics as well as designing photonic structures for improved optimal performance. This thesis presents and exploits several prominent and emerging techniques in computational nanophotonics and nanoplasmonics, including dyadic Green function (GF) theory and quasinormal modes (QNMs). We use a combinations of numerical, analytical, and semi-analytical GF and QNM expansion techniques, complimented with full numerical calculations where feasible, using finite-difference time-domain (FDTD) and finite-element frequency-domain software. Following an introduction to classical electrodynamics, GF techniques, and optical QNM theory, we then present five topics of current interest in nanophotonics. First, we use FDTD techniques and physical insights from the local density of photonic states to explore the effects of structural disorder in photonic crystal slabs on the absorption properties for solar light harvesting, as well as provide a critical analysis of the Lamerbertian limit. Second, we use numerical and analytical GFs to analyze photon-photon coupling effects, including Förster interactions, between quantum dot (QD) disks in a nanowire waveguide, directly comparing to experiments. Our third study extends the QD-QD coupling study by using the Coulomb GF to explore how the near field coupling is affected by spatially dependent QD electronic wavefunctions. Fourth, we employ QNM theory to efficiently describe the critical properties for single photons (e.g., Purcell factor and radiative beta-factor) from a gold bowtie dimer on a substrate coupled to a dipole emitter. In our final work, we use similar techniques to examine the strong coupling regime between a monolayer of MoSe_2 and a single gold nanoparticle, demonstrating the power of the QNM methodology by showing that the strong coupling can be well described by the framework of hybridized QNMs of the entire system without any fitting parameters, including the effects of temperature.