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Plasmonic Lattice Metasurfaces by Predictive Computational Design

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Plasmonic metasurfaces are leading the development of next-generation optical devices with unprecedented compactness and functionality. In contrast to bulk refractive optics, these planar surfaces manipulate light with rationally designed subwavelength building blocks. This thesis focus on how emerging materials and design methods advance the eld of metasurfaces. Chapter 1 reviews the existing metasurfaces based on noble metals and their design by wave-optics principles. This chapter also introduces our metasurface design strategy by evolutionary algorithms, which achieved a wide range of optical responses simply by tuning the arrangement of a single gold nanohole on a discrete square lattice. Chapter 2 describes the realization of metasurfaces based on subwavelength hole arrays in lms of single-crystalline titanium nitride, an unconventional plasmonic material that exhibits superb mechanical strength and high-temperature stability. A multiobjective tness function was developed for our evolutioanry algorithm to produce a variety of three-dimensional light proles with controllable intensities at the light spots. I also demonstrate a simple, ecient technique to prototype these optical designs in large-area by combining focused ion beam milling and wet chemical etching. Chapter 3 applies the evolutionary approach to design achromatic metalenses based on subwavelength plasmonic nanoparticles. Lattice metalenses consisting of a single type of nanoparticle could operate at any wavelengths in the visible to near-infrared regime by tailoring the surface plasmon resonance. The algorithm realized ecient multiobjective optimization and produced achromatic lenses at up to three wavelengths using multiple dierent nanoparticle shapes. Chapter 4 demonstrates a recongurable metalens system for visible-range imaging based on arrays of coupled plasmonic nanoparticles. These lenses manipulated the wavefront and focused light exciting surface lattice resonances that were tuned by patterned polymer blocks on single-particle sites. Predictive design of the dielectric nano-blocks by our evolutionary algorithm created a range of three-dimensional focusing responses. I developed a simple and scalable technique for erasing and writing the polymer nanostructures in a single step using nanoscale embossing. This recongurable materials platform enables tunable focusing and oers prospects for highly adaptive compact-imaging.

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