Patent ID: 8399110

Claim:
A method for making adhesive, hermetic coating on alkaline earth metal fluoride optical elements, the method comprising the steps of: providing a vacuum chamber and within said chamber, providing an optical element made from a single crystal of an alkaline earth metal fluoride, said element being located on a rotatable plate; providing at least one selected coating material source, or a mixture of coating materials source, and vaporizing said material(s) using an e-beam to provide a coating material vapor flux, said flux passing from said material source by a mask having a selected shape to said optical element; providing plasma ions from a plasma source; rotating said element at a selected rotation frequency f; and depositing said coating material on the surface of said optical element as a coating film and bombarding said film on said element with said plasma ions during said material deposition process to thereby form an adhesive, hermetic film on said element; wherein: said oxide film is chemically bonded to the fluoride surface of said element with a bonding energy ≧4 eV; said alkaline earth metal fluoride is selected from the group consisting of MgF 2 , CaF 2 , BaF 2 , SrF 2 , and mixtures of at least two of said alkaline earth metal fluorides; and said mask is selected the group consisting of a partial mask and a reverse mask and the coated surface of the optical element has a surface roughness of less than 1 nm rms.