Propagação de feixes incoerentes em meios não lineares dissipativos

Abstract

Speckle patterns are distributions of light intensity, formed from the interaction between a coherent light source and an irregular surface (or medium), which results in a distribution of wave vectors with random phases. In this way, as randomness plays a relevant role in the formation of spot patterns, their characterization, as well as the analysis of various optical phenomena excited from them are followed by making use of statistical analysis tools. Among the most important tools such as intensity intensity functions and the intensity probability distribution provide indirect information about the manipulation of the transmission source, the degree of scattering (or randomness) of the rough medium, in addition to the optical properties of the medium where the radiation propagates. In this dissertation, the changes that the statistics of speckle patterns suffer when they propagate in self-defocusing non-linear media, with the influence of several non-linear absorption processes, are studied. For this, the dye LDS722 diluted in ethanol was used as a non-linear medium, which, when excited with different intensities, presents the effects of absorption of 1 photon; 2 photon absorption; and absorption of 2 photons. These different effects were characterized using the Z-Scan technique. In order for the non-linear expression of the stain patterns to be influenced by one (or more than one) dissipative effect (simultaneously), three different patterns were generated, with intensity envelopes: (i) Gaussian, (ii) super-Gaussian and (iii) top hat. In this way, it is observed that during the controlled analysis, if the speckles pattern is affected only by a single non-linear absorption process, with top-hat intensity background, its statistical properties follow different behaviors to the patterns influenced by more than one effect simultaneous non-linear absorption with Gaussian and super-Gaussian intensity backgrounds. The studies carried out in this dissertation present, for the first time in the literature, results on the influence of the various non-linear absorption effects on the signaling of speckle patterns. Furthermore, by monitoring the changes in the statistical properties that the speck patterns undergo throughout their defensiveness, it was possible to propose a new methodology to analyze the self-deflection effect induced by the modulation of the non-linear refractive index. Therefore, we propose the use of speckles patterns to characterize the non-linear optical response of different materials.