Recent advances in high-performance window fabrication

摘要

The continuous drive towards higher performance intelligence, surveillance and reconnaissance (ISR) and high-energy laser (HEL) systems has translated into new requirements for high-performance windows. In these applications a wide range of materials needs to be considered, ranging from amorphous glass (such as fused silica), polycrystalline materials (such as Cleartran™) or hard ceramics (such as AlON, spinel and sapphire). A wide range of sizes (up to and including meter class optics) and geometries are also considered for these applications (high aspect ratio piano surfaces remain prevalent, of course, but "free-form" shapes are also being envisioned and implemented routinely, including conformal windows). As is always the case, increasingly tighter specifications, driven by lower wavelength IR systems as well as visible and/or multispectral systems, require continually more sophisticated metrology techniques to verify and validate. Development of manufacturing processes needed to yield pristine optical surfaces capable of operating at higher laser fluences and/or for highly brittle ceramics capable of withstanding a wide range of temperature, operating pressure and stress are also considered. New high-durability thin film coatings capable of withstanding increasingly harsher environments have been developed for these applications. In a defense environment where cost pressures continue to require less expensive manufacturing processes, several advances are discussed. This paper will present a wide range of examples dealing with these materials, geometries, specifications, metrology and thin film coating developments.