Mesoscale modeling of polycrystalline light transmission

Recent advances in polycrystalline ceramic synthesis have established fabrication routes for producing dense ceramics with grain size on the order of few nanometers. Light transmission properties and, specifically, the high transparency of birefringent nanocrystalline ceramics cannot be captured by classical geometrical optics theory. In this investigation, we combine the Raman-Viswanathan wave-retardation theory with finite element method (FEM) based numerical simulations to develop an approach for predicting the refractive index variation within and real in-line transmission through relevant optical materials. This approach is validated on non-cubic (and, therefore birefringent) Al2O3 and MgF2 polycrystalline ceramics, by comparing the computed light transmission to experimental transmission measurements. For both of the considered ceramics systems, the developed numerical model effectively reproduces the experimentally measured transmission as a function of average grain size and incident light wavelength, showing improvement over the original approach of Raman and Viswanathan and a recent particle-scattering based adaptation of geometrical optics theory by Apetz and van Bruggen. The same modeling framework can also simulate the effects of applied elastic and electric fields, allowing for the design and predictive evaluation of functional optical properties in piezoelectric ceramics. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.