Chemical characterizations of optical materials:a tool for high quality components

摘要

Recent works have shown that for low contaminants level, damage density is independent of the amount of contaminants. In these conditions, sub-surface defects (cracks), generated along the optical process, is considered as the main source of damage. Hence, efforts have been made to improve SSD measurement in order to improve its suppression during industrial process. We have developed a method to measure SSD depth which is detailed in this presentation. This method is based on successive acid etching steps. The principle is to establish contamination level (ICP-AES measurement) as a function of etched thickness of SiO_2. The experimental setup has been specially designed to minimize contaminations, reduce hydrofluoric acid quantities and to ease the etch rate determination. SSD depth is given by the asymptotic impurities. This method has been applied to a grinded fused silica intentionally doped in barium tracer. Results have been successfully compared to other characterization techniques such as MRF dimpling or empirical law correlating SSD and surface roughness.