The area of nanophotonics has been the focus of researchers recently due to its high potential to overcome the limitations of scaling in electronic devices. One of the most popular devices in this field is the metasurface. A metasurface consists of a periodic or aperiodic array of spaced units called ’meta-atoms’, where the interaction between these neighboring elements provide unprecedented properties that cannot be obtained using a a regular array of antennas. By tuning the shape and structure of the meta-atoms, electromagnetic wave interaction with the metasurface can be manipulated to achieve a plethora of response characteristics. For active applications that require tunability of the response, a passive metasurface cannot be used to adapt to the varying operating conditions. Tunability of metasurfaces can then be achieved by using phase-changing materials. This type of materials can attain different optical properties by applying external stimulus such as heat, electric current, or laser pulses. The change in the optical properties would be beneficial for applications requiring reconfigurability or adaptation. In this thesis, I demonstrate the employment of volatile (Vanadium Dioxide) and non-volatile (Germanium Antimony Telluride) examples of phase-change materials to design reconfigurable metasurfaces operating at different bands in the infrared regime. I show metallic and dielectric-based structures that employ volatile and non-volatile phase-change materials, as well as apply physics such as plasmonics and bound states in the continuum to design and optimize metasurface structures for energy and biosensing applications. / Thesis / Doctor of Philosophy (PhD) / This thesis proposes methods to design and optimize reconfigurable and adaptive metasurfaces for energy harvesting, radiative cooling, and biosensing applications in the infrared range. The concept of phase-change metasurfaces is highlighted where a phase-change material (PCM) is employed to provide the tunable response. The properties of the PCM can be modified using several excitation methods such as thermal, electric, and laser excitation. The details of material selection, geometry configuration, as well as optimization procedures are demonstrated. Target applications for the study is harvesting from Earth’s ambient radiation around 10.6µm, adaptive cooling of spacecraft in the mid-infrared band 2.5 − 25µm, and trace biomarkers detection in the amide-I and amide-II bands (5.5−6.9µm). Full-wave numerical analysis was conducted using COMSOL Multiphysics software. Optimization was carried out using global optimization techniques implemented using Matlab and Python. The results show innovative designs for switchable absorbers, new approach for modeling of phase-change metasurfaces using deep learning, and employment of the physics of bound states in the continuum for the first time to implement a robust biosensing device. The results of this thesis would help advance the field of reconfigurable nanophotonics and related integrated applications.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Neste tese, estudamos os efeitos não perturbativos associados à presença do horizonte de Gribov e à condensação de operadores locais de dimensão dois, numa teoria de Yang-Mills euclidiana em SU(2), quantizada no calibre abeliano maximal. Estes efeitos são introduzidos de modo a preservar as propriedades de renormalizabilidade e localidade da teoria, e refletem-se diretamente no comportamento dos propagadores. A comparação com os dados da rede indicam um bom acordo qualitativo. / In this, we study the nonperturbative effects associated to the presence of the horizon and to the condensation of local dimension two operators in an Eucledean SU(2)Yang-Mills theory quantized in the maximal Abelian gauge. Such effects are introduced in a way to preserve the properties of renormalizability and locality of the theory. The comparison with the lattice data indicates a good qualitative agreement.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Neste tese, estudamos os efeitos não perturbativos associados à presença do horizonte de Gribov e à condensação de operadores locais de dimensão dois, numa teoria de Yang-Mills euclidiana em SU(2), quantizada no calibre abeliano maximal. Estes efeitos são introduzidos de modo a preservar as propriedades de renormalizabilidade e localidade da teoria, e refletem-se diretamente no comportamento dos propagadores. A comparação com os dados da rede indicam um bom acordo qualitativo. / In this, we study the nonperturbative effects associated to the presence of the horizon and to the condensation of local dimension two operators in an Eucledean SU(2)Yang-Mills theory quantized in the maximal Abelian gauge. Such effects are introduced in a way to preserve the properties of renormalizability and locality of the theory. The comparison with the lattice data indicates a good qualitative agreement.