SBIR-STTR Award

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

A new material and processing technology has been developed and demonstrated that will dramatically reduce the cost of manufacturing and refurbishing large aluminum based mirrors for optical test applications. Such precision mirrors are also required for surveillance, directed energy, cryo-vacuum scene generation, optical testing, and DoD-sponsored space programs. Traditional aluminum mirror technology is used cryogenic chambers for reasons of thermal expansion matching between the optical bench, mounts and components. These mirrors have to be electroplated with nickel, polished and then reflective coated. This process leads to strain mismatches during the chamber cool down resulting in optical deformation in the mirror and de-lamination of the surfaces after repeated thermal cycles. The Phase I polymer coating process was developed with tuned thermal expansion materials to encourage the membrane to bond tenaciously to the substrate and to act as a strain buffer layer between the coating and optic substrate. The air side of the polymer casting creates a highly polished specular surface for the mirror with nearly a factor of 10:1 improvement — eliminating the need for costly final polishing.

Keywords:
Optical Coatings, Aluminum Optics, Low Thermal Of