A influência de parâmetros geométricos do laser de excitação na técnica de lente térmica

Abstract

When electromagnetic waves go through materials different effects may occur depending upon the physical properties of the materials. One of them is of great interest for the analysis of thermal-optical properties and it is known as the photothermal effect. The thermal lens techniques bases is this effect and since its discovery the thermal lens became a powerful tool to describe the thermal-optical properties of huge number of materials, whether liquids or solids. However, no matter how detailed, all the model that have emerged over the years always considered that the excitation beam radius didnt change throughout the sample. In order to verify this condition, we developed a thermal lens mismatched-mode model that consider an azimuthal dependence for the laser radius. Obtaining the intensity expression allowed us to perform a lot of computational analysis and also allowed us to compare this analysis with experimental data. We concluded that the constant radius consideration is valid only if the ratio between the confocal distance and the thickness of the sample is sufficiently large, in other words, the confocal distance must be larger than the samples thickness, otherwise the presented model must be