Cryolite overcoated aluminum reflectors for far-ultraviolet spectroscopy

Javier Del Hoyo; Luis Rodriguez-de-Marcos; J. Hennessy; M. Batkis; C. Bos; Manuel Quijada

doi:10.1117/12.2678149

4 October 2023 Cryolite overcoated aluminum reflectors for far-ultraviolet spectroscopy

Javier Del Hoyo, Luis Rodriguez-de-Marcos, J. Hennessy, M. Batkis, C. Bos, Manuel Quijada

Proceedings Volume 12676, UV/Optical/IR Space Telescopes and Instruments: Innovative Technologies and Concepts XI; 126760I (2023) https://doi.org/10.1117/12.2678149
Event: SPIE Optical Engineering + Applications, 2023, San Diego, California, United States

Abstract

Aluminum (Al) mirrors are conventionally protected with metal-fluoride coatings (e.g., MgF₂, LiF, or AlF₃) immediately after deposition to prevent oxidation and preserve its far-ultraviolet (FUV) spectral efficiency. However, the resulting FUV reflectance of the aluminum reflector is limited by the metal-fluoride overcoat film index of refraction, morphology, stoichiometry, and its absorption cut-off in the lower end of the FUV spectra. Cryolite (sodium hexafluoroaluminate, Na₃AlF₆) emerges as a potential candidate to preserve the aluminum FUV reflectance due to its relatively lower index of refraction in the visible to ultraviolet; therefore, allowing for the thin-film design of highly spectral efficient reflectors over a wide spectral range. We investigate the use of cryolite in aluminum reflector FUV coating design. The deposited aluminum reflector overcoated with cryolite will be examined in terms of spectral efficiency and environmental durability. The deposited cryolite overcoat will be evaluated in terms of optical constants and structural properties. Preliminary results have shown that the use of cryolite as an overcoat to protect aluminum would yield unprecedented results as an optimal Hydrogen Lyman-alpha (HLyα) spectral line reflector, with experimental reflectance values >96%.

(2023) Published by SPIE. Downloading of the abstract is permitted for personal use only.

Citation Download Citation

Javier Del Hoyo, Luis Rodriguez-de-Marcos, J. Hennessy, M. Batkis, C. Bos, and Manuel Quijada "Cryolite overcoated aluminum reflectors for far-ultraviolet spectroscopy", Proc. SPIE 12676, UV/Optical/IR Space Telescopes and Instruments: Innovative Technologies and Concepts XI, 126760I (4 October 2023); https://doi.org/10.1117/12.2678149

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KEYWORDS

Aluminum

Reflectivity

Atomic layer deposition

Far ultraviolet

Reflectors

Surface roughness

Spectroscopy

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