The objective of this project is to optimize the design and fabrication of high reflectance /low absorption broadband UV coating for space telescope mirrors. This is a technology maturation for risk reduction effort. The innovative elements of our approach include: (1) deposit aluminum (Al) with an overcoat of lithium fluoride (LiF) using thermal resistive evaporation, (2) increasing the fluorine efficiency of the films, (3) overcoat the treated coating with a few monolayers of magnesium fluoride (MgF2) and aluminum tri-fluoride (AlF3).
Pure aluminum will achieve high reflectance at the proposed spectral range, however, it becomes oxidized immediately after deposition, thus requires an overcoat to protect from oxidation. LiF is usually the material of choice to use as an overcoat of aluminum due to its high band gap energy and low absorption properties in the FUV, however, its performance is severely hindered due to its hygroscopic nature as its RMS surface roughness increases when exposed to atmospheric conditions. A thin overcoat of a more durable and space flight proven material such as MgF2 or AlF3 layer will be applied to the LiF layer to protect the material while minimizing the absorption effects on the FUV optical properties.
Broadband high reflectance broadband coatings are an essential requirement for interdisciplinary space science missions such as LUVOIR and HABex which will merge ultraviolet astrophysics and visible exoplanet sciences. Enhancing the protected aluminum coating technology will improve on Hubble’s capabilities by capturing photons below the 115 nm spectral range while combining the capability of the Far Ultraviolet Spectroscopic Explorer (FUSE) instrument. By producing low absorption coatings in the FUV, instrument design freedom would be allowed as more elements can be added for aberration correction, a higher spectral radiance will be obtained through the system, and the signal-to-noise ratio will be increased.More »
|Organizations Performing Work||Role||Type||Location|
|Goddard Space Flight Center (GSFC)||Lead Organization||NASA Center||Greenbelt, MD|
|University of Maryland Nanocenter||Supporting Organization||Academic||College Park, MD|