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Assessment of Methods to Manipulate Thermal Emission and Evaluate the Quality of Thermal Radiation for Direct Energy ConversionWijewardane, Samantha 01 January 2012 (has links)
ABSTRACT
Control of spectral thermal emission from surfaces may be desirable in some energy related applications, such as nano-scale antenna energy conversion and thermophotovoltaic conversion. There are a number of methods, from commercially available paints to advanced surface gratings that can be used to modify the thermal emission from a surface. To find out the proper emission controlling technique for a given energy conversion method all the surface emission controlling methods are comprehensively reviewed regarding the emission control capabilities and the range of possible applications. Radiation with high degree of coherence can be emitted using advanced surface emission controlling techniques. The entropy of the thermal radiation, and therefore the exergy, is a function of the degree of coherence. A methodology is presented to calculate the exergy of partially coherent wave fields so that the radiation fields can be evaluated based on exergy. This exergy method is extended to develop a rigorous evaluation criterion for thermal emission controlling methods used in frequency dependent energy conversion applications. To demonstrate these developed criteria using actual data, a surface plasmon emitter is designed and fabricated. Also, possible ways of improving the emitter performance and the research needed to be carryout to fabricate cost effective emitters are described.
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Geração, manipulação e caracterização de campos óticos parcialmente coerentesBasso, Gabriel Fernando 22 May 2015 (has links)
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Previous issue date: 2015-05-22 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In this thesis we address issues pertaining to the fluctuations of the electromagnetic field in the
optical domain, both experimentally as well as theoretically and numerically.
It was experimentally demonstrated the interdependence between the degree of polarization
and the degree of coherence of thermal optical fields. We analyzed the results and explained
them in light of a new unifying theory. We have shown a way to control the coerence of
light through polarization manipulations, concluding with a proposal for a simple thermal light
source with a tunable spectral electromagnetic degree of coherence.
We expanded the concept of a tunable light source, suggesting a partially coherent and
partially polarized light source with complete control of the so called generalized Stokes parameters
by mixing polarized stochastic optical fields. We obtain theoretically the statistical
properties of the resulting optical field and their dependence on the properties of the primary
fields. We discuss fundamental properties of the mixture of stochastic fields and point out some
peculiarities through examples. All results are demonstrated through numerical simulations.
We suggest a method to investigate the spatial statistical properties of gaussian stochastic
fields through the Hanbury Brown-Twiss (HBT) interferometer, an admittedly simple experimenal
method. We show theoretically that it is possible to measure the generalized Stokes parameters,
thus allowing one to rebuild the coherence matrix and the polarization matrix of the
field, completely characterizing the optical field both statistically and locally in the observation
plane. We suggest a technique for the automation of the method, and also some applications.
These many studies on the statistical properties of optical fields led us to a deeper understanding
of the physical meanings of the parameters for characterizing them. From this
understanding we also discuss a change to the definition of the cross-polarization degree and
the significance of optical coherence in terms of this new definition. / Nesta tese abordamos problemas concernentes às flutuações do campo eletromagnético no domínio
ótico, tanto experimentalmente quanto teoricamente e numericamente.
Demonstramos experimentalmente a interdependência entre o grau de polarização e o grau
de coerência de campos óticos térmicos. Analizamos os resultados e os explicamos à luz de
novas teorias unificadoras. Mostramos assim uma forma de controlar a coerência da luz através
de manipulações na polarização, concluindo com uma proposta de fonte de luz térmica simples,
com grau espectral de coerência eletromagnética sintonizável.
Expandimos o conceito de fonte luz sintonizável, propondo uma fonte de luz parcialmente
coerente e parcialmente polarizada com completa liberdade de controle dos chamados parâmetros
de Stokes generalizados, através da mistura de campos óticos estocásticos polarizados.
Obtemos teoricamente as propriedades estatísticas do campo ótico resultante e a dependência
destas com as propriedades dos campos primários. Discutimos propriedades fundamentais
da mistura de campos estocásticos e apontamos algumas peculiaridades através de exemplos.
Demostramos todos os resultados através de simulações numéricas.
Sugerimos um método para investigar as propriedades estatísticas espaciais de campos estocásticos
gaussianos através do interferômetro de Hanbury Brown-Twiss, um método experimenal
reconhecidamente simples. Mostramos teoricamente que é possível medir os parâmetros de
Stokes generalizados, permitindo reconstruir a matriz de coerência e a matriz de polarização do
campo, caracterizando completamente o campo ótico tanto estatisticamente quanto localmente.
Apontamos ainda técnica para a automação do método, além de aplicações.
Os diversos estudos realizados acerca das propriedades estatísticas de campos óticos nos
levaram a um entendimento profundo dos significados físicos dos parâmetros utilizados para
caracterizá-los. A partir deste entendimento, discutimos ainda uma modificação na definição
do grau de polarização cruzado e da significância da coerência ótica em termo desta nova
definição.
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