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Title:Flat optics based on patterned nanostructures for concentrating light
Author(s):Ding, Qing
Director of Research:Toussaint, Jr., Kimani C.
Doctoral Committee Chair(s):Toussaint, Jr., Kimani C.
Doctoral Committee Member(s):Goddard, Lynford L.; Dragic, Peter; Chen, Qian
Department / Program:Electrical & Computer Eng
Discipline:Electrical & Computer Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):plasmonics
light concentration
bowtie nanoantennas
nanopatterning
nanostructures
concentrating solar power technology (CSP)
planar focusing collectors (PFCs)
Abstract:This work explores the development of flat or planar light concentrators using nanostructured materials. Flat optical concentrators with small form factors could find utility in applications ranging from integrated optical components to lightweight concentrators. Conventional concentrators are often based on the use of refractive lenses or reflective focusing optics, all of which are either too bulky and cumbersome to be incorporated into portable devices or inconveniently large and heavy to be maintained at a relatively low cost. To achieve development of a planar concentrator, we investigated the application of nanostructuring of materials. In particular, we considered both nanostructured plasmonic or metal nanoantennas with deeply subwavelength features, and dielectric nanostructured surfaces that are fabricated by two-photon lithography. In the former case, we developed pillar-supported Au bowtie nanoantennas (pBNAs), and found that light concentration in these structures leads to both a large field enhancement and thermal response. We found that intrinsic absorption in the pBNAs leads to significant heating, the result of which could promote optically guided delamination of the metal from its dielectric pillar. We showed that this delamination of metal via light concentration, which we refer to as plasmon-assisted etching (PAE), can be used to facilitate table-top fabrication of planar optical components, such as a Fresnel zone plate. As a follow up to this work, we explored the possibility of extending the field enhancement associated with plasmonic bowtie nanoantennas (BNAs), which typically decays evanescently, away from the surface. Our simulation results revealed that by vertically stacking multiple BNAs of select thicknesses and gap sizes, the near-field enhancement associated with a single BNA can be extended ~ 200 nm away from the surface. Moreover, we find that such a structure behaves as virtual lens with 25-nm focal length, which could be useful for sensing applications. With respect to nanopatterning plasmonic materials, such as aforementioned single BNAs and pBNAs, the conventional patterning method is to use electron-beam lithography for defining fine features on the nanometer scale. This technique normally requires that the features to be patterned are tuned within a planar regime, meaning that obtaining height variation for plasmonic nanostructures using this approach is generally difficult to achieve. With the development of two-photon lithography (TPL), a 3D nanoprinting technique that utilizes a focused laser beam to solidify polymer structures, we are able to nanopattern structures with height variations, and as a result, devise a new design called plasmonic nanovolcanos that is inspired by the idea of a solid funnel. We systematically explore the parameter space of the nanovolcanos with respect to how their heights and aperture sizes affect the plasmonic mode and associated field enhancement. By placing nanovolcanos with two different heights on the same substrate, we demonstrate the example of vertically heterogeneous plasmonic nanostructures that exhibit individual resonant peaks within each region and a third collective resonant peak at their boundary. Finally, in the case of planar concentrators based on dielectric nanostructured surfaces, we explored designing these structures as planar focusing collectors (PFC) for applications relevant to concentrated solar power (CSP), which is a new application domain. To facilitate potential scalability, our developed PFCs are fabricated using TPL. By building around the constraints of TPL technology, we propose two types of approaches for PFC designs: the first approach is based on the idea of conventional Fresnel lens while the second one is based on a concept in the field of nanophotonics called metasurface. We experimentally demonstrate focusing with our PFCs for three wavelengths in the visible, and discuss feasibility for realistic CSP applications.
Issue Date:2019-12-04
Type:Text
URI:http://hdl.handle.net/2142/106364
Rights Information:Copyright 2019 Qing Ding
Date Available in IDEALS:2020-03-02
Date Deposited:2019-12


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