Investigation of the microstructure of coatings for high power lasers by non-optical techniques

摘要

The microstructure of optical coatings strongly influence their resistance to high fluence laser scatter properties, as well as their mechanical and environmental stability. The relative merits of non-optical techniques, such as: scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and focused ion beam, are discussed as they apply to optical multilayer coatings. The combination of these techniques provides a unique method to analyze defects in coatings. The long term objective of this work is to: understand the initiation and growth mechanisms of defects in optical coatings, investigate failure mechanisms of laser coatings, and suggest methods for reducing the number of defects during the deposition process. To date, our defect analysis using non-optical techniques has focused on hafnia/silica multilayers for high power lasers. In summary, the information we have compiled about the defect seeds: indicates that seed size has an influence upon the mechanical stability of the whole defect, indicates that seed shape and chemical composition reveal potential seed sources in the coating system, and demonstrates that defects can be initiated either as a single event or continuously during the deposition process. Also, it is shown that different vendors have characteristic defects and seeds.