Voos de Lévy em vapores atômicos com espectros de absorção e emissão modificados

• Autor(a) principal: Carvalho, João Carlos de Aquino
• Data de Publicação: 2014
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UFPB
• Texto Completo: https://repositorio.ufpb.br/jspui/handle/tede/5741
• topic: Redistribuição Parcial em Frequência; Redistribuição Completa em Frequência; Lei de Potência; Partial Frequency Redistribution; Complete Frequency Redistribution; Power Law; CIENCIAS EXATAS E DA TERRA::FISICA

When one focus a radiation in an atomic vapor, the radiation may undergo absorption and emission several times before the photons leave the cell volume that contains the vapor. As a result of these several scattering occurring inside the cell, the spectral profile of the incident radiation undergoes an evolution, which is governed by the mechanisms of frequency redistribution. There are two kinds of frequency redistribution: a Partial Frequency Redistribution (PFR) and a Complete Frequency Redistribution (CFR). When there is a correlation between the emission and absorption frequencies, we say that a PFR occurred. Otherwise, when there is no correlation between the absorbed and emitted frequencies, we say that a CFR occurred. This frequency redistribution has its origin in the inhomogeneity of the spectral profiles of the incident radiation and the response of the resonant vapor. It may be noted also that this inhomogeneity determines the distribution of step lengths of photons in an atomic vapor. The photons which propagate through this atomic medium perform a random walk between successive processes of absorption and emission, whose step length r is described by a probability distribution so-called "long tail". However, the superdifusive behavior of these photons is characterized by a single step length, which decreases asymptotically following a power law P(r) r with < 3. In this work we study, on a hand, the frequency redistribution in two parts: the first one is for several detunings of the radiation relative to the absorption center and we fix the vapor density, and, at a second part, we fixed the radiation detuning of the radiation and we changed the atomic density. In our numerical model, we studied rubidium atoms, by considering its optically active electronic structure with only two levels of energy and we excited it at the frequency of its D2 line. For the second part of this work, we analyzed numerically the exponent of the power law for the probability distribution of the single step lengths of the photons in an atomic vapor for absorption spectra and modified emission. For the last part of this work, we developed an experimental model to analyze the frequency redistribution, where the emitted photons coming out of the cell volume are collected in a certain solid volume by a lens of a few centimeters, directed through a fiber for analysis by a Fabry-Perot. Furthermore, an experimental setup has been developed to generate the probability distribution of photon steps, where we modified the spectra of the incident radiation or absorption. In the case of the incident radiation, it is guided by a fiber towards a second cell where a CCD camera with high sensitivity allows measuring the length of individual photon steps.