Breaking Symmetry: A Study of Novel Phenomena in Asymmetric Nanoplasmonic Systems

Offering tailorable optical properties not achievable with symmetric or periodic optical materials, chiral, weakly disordered, deterministic aperiodic, quasiperiodic and random structures make up a new wave of asymmetric optical systems demonstrating unprecedented control of light compared to their periodic counterparts in areas such as random lasing, imaging, and bio-sensing. The governing physics of asymmetric systems is, however, not as analytically intuitive and computationally straightforward as periodic or highly symmetric systems, and thus the availability of simple analytic and computational design tools has made periodic systems an attractive option for many optical applications. For example, plasmonic systems consisting of periodic arrays of achiral metallic sub-wavelength scatterers, referred to as metasurfaces, can manipulate the phase front of light waves over nanometer scale distances. This is possible due to the plasmonic confinement of light to sub-wavelength dimensions. In Part I of this work, a novel class of plasmonic aperiodic metasurfaces is introduced exhibiting novel functionalities not possible in their periodic counterparts. Freeing the design process from time costly FDTD simulations, the development of an analytically intuitive model describing interference at a slit-aperture between directly incident light and surface plasmon polaritons arriving from nearby illuminated grooves has enabled the speedy design, fabrication, and experimental characterization of aperiodic slit-grooved plasmonic devices with easily tunable angle-dependent multi-spectral responses. These devices, constituting part of a new and novel class of aperiodic systems referred to as aperiodic-by-design, have lateral dimensions ≤ 10 μm and consist of a sub-wavelength slit (circular) aperture surrounded by grooves (semi-annular rings) on an opaque metal film. Each groove is individually optimized for position, width, and depth in order to achieve a specific desired multi-spectral response. Part II of this work explores the chiroptical (CO) response of optical media. The potential several-orders of magnitude plasmonic enhancement of the weak circular dichroism (CD) response of natural molecules has generated a plethora of research interest and publications describing the so-called CD response of plasmonic systems. However, this work demonstrates, through the development of a generalized coupled-oscillator (GCO) model, the presence of other CO responses not related to CD. Closed-form analytic expressions for various CO response types are developed within the GCO model, and characteristics of each type are highlighted. This work both demonstrates the necessity of careful interpretation of CO measurements and provides tools for distinguishing between the response types. The GCO model unifies, for the first time, many of the separately observed chiral-optical phenomena into a single theoretical framework. The results presented in this dissertation testify to the novel and seemingly exotic behaviors of asymmetric plasmonic systems. The in-depth analysis of the systems provided in this work emphasizes the fundamental origins of these behaviors, providing a clear roadmap towards the development of a new generation of optical devices with functionalities extending beyond the existing state-of-the-art technologies. Breaking Symmetry: A Study of Novel Phenomena in Asymmetric Nanoplasmonic Systems by Matthew S. Davis B.S., Illinois State University, 2006