Caracterização experimental e numérica da caminhada aleatória dos fótons em células de vapor de Césio : efeitos de colisões atômicas, transporte superdifusivo e voos de Lévy

• Ano de defesa: 2025
• Autor(a) principal: Nunes, Isaac Cazé
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal da Paraíba; Brasil; Física; Programa de Pós-Graduação em Física; UFPB
• Palavras-chave em Português: Voos de Lévy; Aprisionamento radiativo; Vapores atômicos; Transporte anômalo; Simulações de Monte Carlo; Lévy flights; Radiative trapping; Atomic vapors; Anomalous transport; Monte Carlo simulations; CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA
• Link de acesso: https://repositorio.ufpb.br/jspui/handle/123456789/37182

Radiative trapping in dense atomic vapors is a fundamental process governing the transport of light, often manifesting as anomalous superdiffusive transport described by Lévy flights. Howe- ver, the quantitative connection between the Lévy exponent, α, the controllable experimental parameters, and the role of atomic collisions in radiative transport constitutes a highly complex issue, whose mechanisms are not yet fully understood. This thesis presents a systematic theore- tical and experimental investigation of Lévy flight dynamics in cesium-133 vapor, characterizing the dependence of α on the atomic density (N), cell length (`), and laser intensity (I). The methodological approach integrates diffuse transmission measurements at 10◦ and 90◦ relative to the incident laser beam direction with the development of theoretical modelsincluding a novel correction for finite-system effectsand Monte Carlo simulations. The analysis reveals a remar- kable duality in transport: while the 90◦ transmission (single scattering) is described by partial frequency redistribution, as expected at low atomic densities where the probability of atomic collisions is low, the 10◦ transmission (multiple scattering) yields the main paradoxical result of this thesis: even in regimes of low collision probability, the measured α values are consistently described by the collisional scenario. Furthermore, the complex dependence of α on N and ` is quantified for the first time. It is concluded that transport statistics can be actively tuned, but that the nature of the photon random walk in atomic vapors is more intricate than current models capture, thereby establishing a solid experimental and computational foundation and formulating the precise questions that will guide future investigations.