Broadband reflectivity and emissivity engineering using patterned surfaces

Official URL: https://risc01.sabanciuniv.edu/record=b2708502_(Table of contents)

Optical coatings composed of thermomechanically superior materials with high reflectance in the broadband spectrum have recently attracted attention. Tungsten (W), among other refractory metals, suits well for applications that require high thermomechanical stability but suffer from low reflectivity below 1.5 µm. This thesis aims to propose design methods to optimize patterned multilayer nanostructures that lower Tungsten’s absorption over a broadband spectrum. The first proposed design mimics the patterns observed on Morpho butterfly wings and increases the reflectivity of W over a broad spectrum. At the initial stage, the impedance mismatch method is implemented to optimize the number and thickness of the homogeneous multi-layers over the broadband spectrum. Then, the proposed pattern is incorporated into the homogenous structure. For the second structure, after optimizing the thickness and number of SiO2/TiO2 layers stacked on Tungsten as the initial design, the inverse design approach is utilized to construct holes that increase reflectivity in the dip points caused by interference effects. Different design parameters are studied for both structures, the origin of optical phenomena is explained, and the effect of fabrication impurities is taken into account. The proposed structures and methods can be used in various optical applications.