Study of an Optical Device Used to Homogenize a Laser Beam. Application to Emissivity Measurements on Semitransparent Materials at High Temperature

Abstract

On an experimental apparatus designed to measure the directional spectral emissivity of semitransparent materials at high temperature (2000°C), a specific optical device (kaleidoscope) is mounted in order to homogenize the energy distribution of a CO2 laser beam, which is used as a heating source. An objective of this work, for operating in the best conditions, is to obtain a uniform temperature of the tested sample. This study, based on Fourier optics, focuses on a square aperture kaleidoscope. A model was developed to simulate the energy distribution of the laser beam, at any transverse plane on the optical path. The final objective is to simulate the energy distribution on the sample surface to optimize the homogenization device taking into account the surface temperature gradient induced by the local energy distribution. To validate this model, quantitative comparisons of theoretical simulations and experimental thermal spots are performed.