Transparent Films Thickness Mapping Highlighting the Viscosity Effect of Elastic Layers Made by Sol–Gel Process with an In-House Ellipsometer

Abstract

New optical coatings are currently developed to mitigate the shockwave generated by nanosecond lasers in high-power laser systems such as the MegaJoule laser (LMJ). These shockwaves seem responsible for the damage growth observed on optical components. A possible solution for shockwave mitigation is using ormosil (organically modified silicate) coatings made by the sol–gel method with thicknesses of a few microns. Unfortunately, the sol–gel solution exhibits a viscous behavior, and thus, the deposited layers are heterogeneous in thickness. An experimental ellipsometer has been designed to measure this heterogeneity and highlight the viscoelastic properties of the layers responsible for self-healing effects that were observed when these layers were scratched. This ellipsometer allows us to know the refractive index of the coating and therefore its density. Density and thickness are the two essential parameters for determining the speed of sound and the modulus of elasticity of the layer, which indicate the ability of the layer to attenuate more or less elastic waves or shock waves.