Field Enhancement in Nano Photonic Applications: Transition Metamaterials, Plasmonics and Chirality
Alali, Fatema Abdullah
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This dissertation includes four chapters. Chapter 1 contains a brief introduction to the field of nanophotonics and an overview of the topics studied and methods used in this research. Chapters 2, 3 and 4 each deal with distinct and major applications of nanophotonics. Chapter 2 focuses exclusively on metamaterials, specifically transition metamaterials were the refractive index gradually decreases from positive to negative values passing through a near zero value point along the direction of propagation. We investigate the propagation of a Gaussian beam through such materials and show for the first time that unlike the case of plain waves, Gaussian beam field enhancement near the zero refractive index is attainable for normal incident. Such materials can be used for light manipulation applications such as cloaking and field concentrators. The next chapter, Chapter 3, deals with plasmonics, the science and applications of plasmons. We study the Localized Surface Plasmon Resonance (LSPR) of metallic Au nanotori and nanoring structures and compare their absorption as a function or orientation to that of other nanoparticles (nanospheres and nanorods), specifically for biomedical applications, especially photothermal therapy. We show that nanotori (nanorings) have higher averaged absorption for random orientations, which makes them well-suited for colloidal heating applications such as photothermal cancer therapy. Finally, in Chapter 4 we investigate methods for enhancing optical rotation in artificial chiral materials. We introduce the concept of multiscale chirality, a superposition of geometric and molecular chirality, to boost the effective chirality parameter κ of a material and consequently its optical activity. The goal is to obtain a sufficiently high κ to achieve an effective negative refractive index without requiring simultaneous negative values of permittivity and permeability, which are difficult to achieve at optical wavelengths. We also use plasmonics to enhance both molecularly chiral media and media consisting of 2D dielectric chiral shapes to achieve giant optical rotation in both systems. We demonstrate that this can be utilized in applications such as biosensing and adapative optofluidic polarizers.