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

Abstract

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.