Repositório Institucional IFSC
URI permanente desta comunidadehttp://143.107.180.6:4000/handle/RIIFSC/1
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Resultados da Pesquisa
Item Medidas das constantes dielétricas e deslocamento elétrico em dielétricos: desenvolvimento da técnica e metodologia(2014-04-09) Cabral, Flávio Pandur AlbuquerqueDesenvolveu-se um sistema para medir a constante dielétrica complexa de amostras dielétricas, de construção simples, versátil e de baixo custo. A medida é feita aplicando-se uma tensão senoidal e fazendo-se a aquisição do sinal aplicado e do sinal da resposta elétrica (carga elétrica). Emprega-se uma placa A/D para a aquisição de dados com taxa de amostragem de 100 Ksamples/seg e através da transformada de Fourier discreta destes sinais determina-se a impedância complexa da amostra, a partir da qual calcula-se a constante dielétrica complexa. A placa utilizada e o circuito de medida da carga elétrica introduzem defasagens indesejáveis nos sinais, cujas correções são feitas através de programa no computador usado para aquisição dos sinais. O sistema mostra um desempenho similar àqueles dos equipamentos comerciais para freqüências no intervalo de 0,1H.z a 1KHz, sendo testado com componentes resistivos e capacitivos e posteriormente em amostras de Teflon FEP, poli(fluoreto de vinilideno) e seus copolímeros com trifluoretileno. O sistema também foi utilizado para medir o deslocamento elétrico nos polímeros ferroelétricos sob a aplicação de campos elevados. Neste caso determinaram-se as curvas de histerese dielétrica e os deslocamentos de primeira, segunda e terceira ordem.Item Two-photon two-atom processes(2013-10-29) Paiva, Rafael Rothganger deIn the atomic, molecular, optical physics field, processes involving two photons are very well understood and used in applications ranging from spectroscopy to laser cooling technics. In this thesis is presented the study and experimental realization of two two-photon processes. Using sodium atoms trapped in a magnetic optical trap we could demonstrate two-photon cooperative absorption, and that the creation of a molecular bound state using only light fields, or photonic bound state, is possible. Two-photon cooperative absorption, very common in solid-state physics, is a process where a pair of atoms initially in the ground state is excited to the double excited state, via absorption of two photons with frequecy that is not ressonant with any excited state. Its experimental realization with cold atoms may open new and exciting possibilities to better understand nonlinear effects, and it is a new way to create correlated atoms and photons in cold atomic physics. This absorption was observed by ionization of the pair after the excitation. A simple model that considers only dipole-dipole interactions between the atoms allows us to understand the basic features observed in the experimental data. A photonic bound state uses two photons to create the two basic features of a molecular bound state: a repulsive part and an attractive part. A blue photon, blue detuned from the atomic transition, connects the ground state of the pair to the repulsive part of the first excited molecular state 1, and a red photon, red detuned from the atomic transition, connects the connects the ground state of the pair to the attractive part of the first excited molecular state. In the dressed state picture, when the light fields are strong, this three-states-two-photon system creates adiabatic bound potentials that are strongly dependent of the photon properties. Using a theoretical model we could study how this bound energies changes when we change the photon properties, and the experimental data shows that this photos are indeed dressing the potentials with a efficiency that would enable the creation of photonic molecules.