Polymer Barrier, Protection and Cleaning for UVOIR and X-Ray Mirrors

Maturing vacuum ultraviolet mirror coating technology for use in UV Astrophysics is on the critical path for NASA Flagship Missions such as the Habitable Worlds Observatory (HWO). In the Lyman Ultraviolet (LUV ~90-122nm), the reflection efficiency of current telescope mirror coatings drops precipitously. The best option, bare aluminum, forms a natural oxide coating in seconds and absorbs these wavelengths. One solution would be to fabricate the telescopes and mirrors in the vacuum of space to avoid oxygen. Recently, excellent progress has been made utilizing lithium and aluminum fluorides as protective and reflectivity-enhancing coatings on aluminum. However, these materials are easily scratched and must be protected from water vapor intrusion in assembly, testing, and while waiting for launch. This proposal suggests creating a family of removable polymer film coatings as water barriers and cleaners for water-sensitive and freeform optical surfaces. The Apply-Dry-Peel-No-Residue polymer coatings developed herein will also reduce or eliminate pinholes when used to clean and prepare the surface before depositing the aluminum mirror and fluoride overcoats-enhancing coating performance, longevity, and enhancing stray-light suppression. The nearly ubiquitous pinholes that occur in fabricating metal coatings lead to corrosion, light scattering, and coating failure. This technology will mitigate NASA's mission risk by enabling the cleaning of historically uncleanable surfaces and by pre-qualifying the safety of cleaning flight optics early in missions. Avoiding irreversible failures when contamination happens will save time and money. Without such pre-clearance, precision mission surfaces might have to, again, launch dirty or with a fingerprint, as with HST's primary mirror and the Wide Field Camera II. Indeed, Hubble's primary mirror had a 10% degradation in reflectivity due to pre-launch contamination.
Benefits: The suit of stripcoatings will provide superior oxygen and water barriers, cleaning and protection from marring for most other technologically-important surfaces including UVOIR, through the entire prelaunch path regardless of structural complexity, size or sensitivity of exposed components. Potential future applications include optimized carbon nanotube-based electrostatic-free & conductive films, creating/maintaining sterile & biological contamination-free surfaces, and cleaning and sequestering radioactive surface contamination for disposal. Post-SBIR commercialization will focus on markets where prevention of water and oxygen surface corrosion or surface protection during shipping or storage is critical, e.g., photonics, astronomy, and manufacturing using clean rooms and dry rooms to prevent oxidation. Surface radiation contamination removal could interest government & commercial operators within the nuclear/defense industries. Optics thin-film and microelectronics manufacturers will investigate the pinhole-free substrate preparation product, as will those charged with surface radiation/chemical decontamination. They will also be interested in the moisture-barrier polymer, as will those needing to block water or oxygen access to surfaces to forestall corrosion or provide surface protection during shipping or storage. We anticipate that the formulations from this research will have significant commercial applications for optical elements coated with fluorides and generally where there are humidity-sensitive surfaces. Because of their low refractive index, fluoride films have an application in anti-reflective glass optics, such as camera lenses and other transparent crystalline optical materials. Fluorides are also used as the low-index member of “high/low” optical multilayers. Because of its better resistance to humidity, this has been MgF2. LiF has a lower index, but whether it replaces MgF2 or not, it is clear that there will be a market for formulations specially developed for cleaning, protecting, and storing fluoride-coated optics. Those who buy FCP for their glass and their oxide-coated optics will be interested in a coating specially designed with fluorides in mind. Fluorides are also preferred for near UV and DUV coatings. Cleaning and protecting these newly developed VUV optics are essential in the semiconductor, photonic and UV astrophysics space where no alternative currently exists.