Newswise — COLUMBUS, Ohio, OCTOBER 24, 2019 -- Future space-based telescopes that may replace the Hubble Space Telescope will require access to the far-ultraviolet (FUV) region, where light has a very short wavelength. However, astronomical observations in this region present challenges due to the oxidation of the aluminum films used in optical studies in the FUV region.
At the AVS 66th International Symposium and Exhibition in Columbus, Ohio, David Boris, a physicist at the U.S. Naval Research Laboratory, will discuss work being done to optimize aluminum thin films for use in space applications.
Due to their high FUV reflectance, aluminum mirrors are used for astrophysical observations. However, aluminum is highly reactive and oxidizes quickly. The aluminum oxide layer created during oxidation absorbs FUV radiation, blocking the mirrors from reflecting the desired wavelengths.
“That occludes most of the FUV portion of the electromagnetic spectrum,” said Boris.
A fluoride coating over the aluminum is needed to protect the aluminum from oxidation while maintaining as much of its reflectivity as possible. However, materials that have been used to address this problem in the past have presented issues of their own. Some coatings degrade too quickly, and others have absorption cutoffs that prevent the observation of interesting astronomical phenomena.
“The protective fluoride coating must allow FUV to pass through it so it can reflect off the aluminum surface underneath it,” Boris said. “Alternative materials with lower cutoff wavelengths and better stability in ambient conditions are desired.”
This motivated Boris and his team to look at aluminum fluoride as an alternative coating material. While other groups are examining multistep approaches which involve removing the oxide layer followed by depositing fluoride over the material, Boris’ efforts use plasma generated by an electron beam plasma to convert the oxide to AlF3 in a single step. Under the right conditions, they found the AlF3 can increase the reflectivity of the mirror from 10% to nearly 60% in wavelength regions inaccessible by other coating methods.
In his talk, Boris will present this method of single step deoxidation and coating and discuss the effects of various plasma parameters on the optical properties of the aluminum mirrors.
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Presentation: “Enhancing the Far Ultra-Violet Optical Properties of Aluminum Mirrors with a Single Step Approach to oxide Removal and Fluorine Passivation,” David Boris, U.S. Naval Research Laboratory; A.C. Kozen, S.G. Rosenberg, American Society for Engineering Education; J. del Hoyo, J.G. Richardson, M.A. Quijada, NASA Goddard Spaceflight Center; S.G. Walton, U.S. Naval Research Laboratory, Thursday, Oct. 24, 11:00 a.m., Room A215 in the Greater Columbus Convention Center, Columbus, Ohio
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