Matched and Ultra-Low CTE Optical Materials

A new material and processing technology is proposed that will dramatically reduce the cost of manufacturing lightweight mirrors for optical test applications. Such precision mirrors are also required for surveillance, directed energy, and DoD-sponsored space programs. There is a significant amount of research devoted to developing materials and processes for space-born mirrors and ground test use. Carbon fiber mirrors and advanced ceramic (SiC) mirrors are being developed. These materials provide excellent stiffness to weight ratios and thermal stability. The principal problem with using these lightweight materials for mirrors is the difficulty of polishing and length of time it takes to achieve the optical quality surface finish and scale up to large diameters. GATR is proposing to demonstrate a process for depositing a very thin, optical-quality membrane layer to reduce the polishing step. The key elemental innovation is the use of an optically tolerant fabrication process using a specially developed polyimide which has a matched substrate CTE. These polyimides are cryogenic compliant and can be cast on flats, off-axis and on-axis mirrors. The STTR will investigate the possible use of ultra-low CTE membrane optics as well as matched CTE over layers on Aluminum of SiC unpolished surfaces.