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advanced environmentally resistant lithium fluoride mirror coatings for the next generation of broadband space observatoriesRecent advances in the physical vapor deposition (PVD) of protective fluoride films have raised the far-ultraviolet (FUV: 912-1600 A) reflectivity of aluminum-based mirrors closer to the theoretical limit. The greatest gains, at more than 20%, have come for lithium fluoride-protected aluminum, which has the shortest wavelength cutoff of any conventional overcoat. Despite the success of the NASA FUSE mission, the use of lithium fluoride (LiF)-based optics is rare, as LiF is hygroscopic and requires handling procedures that can drive risk. With NASA now studying two large mission concepts for astronomy, Large UV-Optical-IR Surveyor (LUVOIR) and the Habitable Exoplanet Imaging Mission (HabEx), which mandate throughput down to 1000 , the development of LiF-based coatings becomes crucial. This paper discusses steps that are being taken to qualify these new enhanced LiF-protected aluminum (eLiF) mirror coatings for flight. In addition to quantifying the hygroscopic degradation, we have developed a new method of protecting eLiF with an ultrathin (10-20 A) capping layer of a nonhygroscopic material to increase durability. We report on the performance of eLiF-based optics and assess the steps that need to be taken to qualify such coatings for LUVOIR, HabEx, and other FUV-sensitive space missions.
Document ID
20180002223
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Fleming, Brian
(University of Colorado )
Quijada, Manuel A.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Hennessy, John
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Egan, Arika
(University of Colorado )
Del Hoyo, Javier G.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
April 10, 2018
Publication Date
December 13, 2017
Publication Information
Publication: Applied Optics
Volume: 56
Issue: 36
ISSN: 1559-128X
Subject Category
Optics
Report/Patent Number
GSFC-E-DAA-TN54787
Funding Number(s)
CONTRACT_GRANT: NNX15AF27G
Distribution Limits
Public
Copyright
Other