Inhomogeneous optical coatings: an experimental study of a new approach

Inhomogeneous optical interference coatings offer a potentially superior alternative to their multilayer counterparts in meeting rigid performance requirements. However, their development has been severely hampered by the lack of appropriate design software and process control hardware. The work reported in this paper involved the experimental design and fabrication of a number of inhomogeneous coatings, and some interesting results were obtained. Using customized algorithms and simultaneous codeposition techniques, an inhomogeneous antireflection coating based on germanium and thorium fluoride has been successfully produced. Attempts with other materials such as zinc sulfide were less successful because of discrepancies between predicted and actual deposition rates, and further studies are being conducted.