Thermoelastic response of materials with thick-disk geometry excited by a ring-shaped laser beam

Abstract

In photothermal science, the form of the profile of the illuminating laser beam is crucial, defining the usefulness as well as the accuracy of a given methodology. In this paper, the thermal photoinduced effects on a low absorption sample by illuminating it with a ring-shaped laser beam are theoretically investigated. The main advantage of the ring-shaped laser beam is that it produces a temperature profile with a flat-topped form at a steady-state. The heat diffusion and thermoelastic equations are analytically solved providing the temperature distribution, surface displacement, stresses, and optical path for a sample with a thick-disk geometry. It is shown that, when the internal radius of the laser beam is zero, the results for the ring-shaped laser are reduced to the top-hat laser beam case. Additionally, the finite element method is applied to determine the temperature, displacement, stresses, and optical path profiles based on the same set of equations. The comparison between numerical and analytical solutions was performed as a form of validation, which showed a good agreement between both types of results. Our analytical results can be useful in the study of materials using photothermal techniques, as well as in the design of optical components and the configuration of experimental systems.