Advisory Committee Chair
Kannatassen Appavoo
Advisory Committee Members
Erik Busby
Shane Aaron Catledge
Christopher M Lawson
Clayton E Simien
Document Type
Dissertation
Date of Award
2022
Degree Name by School
Doctor of Philosophy (PhD) College of Arts and Sciences
Abstract
Manipulating electromagnetic fields at the nanoscale has gained significant interest as they can enhance device efficiency in the energy, telecommunication, and medical sectors. The ever-increasing demand for smaller, faster, and efficient optoelectronic devices lead to plasmonics — metallic nanostructures which can manipulate light below the diffraction limit. Recently, all-dielectric nanostructures have also shown to create high quality-factor resonances, with strong electric and magnetic near-fields created due to displacement currents. While silicon is the material of choice — because of its high refractive index, compatibility with complementary metal-oxide-semiconductor, and strong non-linear response — its broadband dynamics is not fully understood in order to fully utilize its high switching speed (up to petahertz). This dissertation examines the linear (equilibrium) and time-dependent (non-equilibrium) optical features of two-dimensionally confined metamaterials (i.e., metasurfaces) when intrinsic (e.g., dielectrics) and extrinsic properties (e.g., size, shape, and lattice periodicity) are modified. To quantify the role played by intrinsic-dielectrics properties, we first build a numerical model to determine how processes like trapping, bimolecular and auger recombination, and thermal effects all modify the spectro-temporal properties of amorphous-Si thin films. Furthermore, for our metasurfaces, we build 3D full-field time-domain electromagnetic simulations to quantify how the ultrafast optical response is modified with changes in excited carrier densities. iv To quantify the effect of extrinsic properties, we systematically vary the unit cell geometry of our metasurfaces (i.e., by changing shape, size, arrangement, orientation, and spacing of the nanostructures) to elicit unique electromagnetic optical resonances and probe their time-dependent evolution. Using linear and ultrafast time-resolved broadband spectroscopy, we study how the complex electric and magnetic resonances evolve from the femtosecond to the nanosecond timescales. Our electromagnetic simulations connect the far-field Mie optical response to their nanoscale localized electromagnetic near-fields. Importantly, this dissertation provides the first study of time-dependent collective resonances in lattices of dielectric nanostructures, i.e., surface lattice resonances. Through careful and systematic fabrication of metasurfaces with different geometries, we demonstrate how to tailor these short-lived resonances. Our work develops the experimental and theoretical framework to design and optimize future optoelectronic devices that can temporally control light emission, lasing, and signal processing.
Recommended Citation
Tiwari, Uddhab, "Ultrafast Broadband Dynamics in Novel Classes of Metamaterials" (2022). All ETDs from UAB. 160.
https://digitalcommons.library.uab.edu/etd-collection/160