Flatness and Stress Control Strategies for Coated High-Aspect Ratio Substrates
Oftentimes, in its simplest view, fabrication and coating are considered different manufacturing steps – fabrication creates the optic’s geometry while coating controls the optic’s spectral response. However, in practice, these two are not independent processes. They must work together to achieve the highest quality optics. One such example is the specification of surface flatness. Surface flatness specifications are usually presumed to be post-coat, but maintaining surface flatness through the coating process can be a challenge. This is because coatings contain an internal stress which can impose a flatness change on the optic. There are many factors that interplay to determine the total flatness change during the coating process, but the problem is most aggravated in high-aspect-ratio (OD:CT) optics. We define the source of this flatness change and explore some of the options for maintaining pre-coat flatness:
- Coating material choice
- Process choice
- Back-side coating
Kyle Fortenberry, Optical Thin Film Coating Engineer, PFG Precision Optics
Kyle Fortenberry has been with PFG Precision Optics for 10 years as an Optical Thin Film Coatings Engineer where he oversees production, process improvement, and research and development. Kyle holds a Master of Science in Physics from Georgia Institute of Technology. In addition, he has a Bachelor of Science in Physics and Mathematics with a Minor in Chemistry from the University of Southern Mississippi. His thorough understanding of various coating process technologies, coupled with his love for learning and problem solving, serves as a resource for customers seeking solutions to their optical coating needs.