Patent — available for licensing
Advanced AlF3-Passivated Aluminum Mirrors
A NASA invention available to explore as a licensing opportunity.
About this technology
Overview
Pure aluminum (Al) exhibits an intrinsically high reflectance in the 90 – 2500 nm wavelengths and is commonly used for mirrors in optical applications within this range. However, in order to be used in the far-ultraviolet (FUV) range between 90 – 130 nm, an optical thin film overcoat is needed to protect the Al and prevent the formation of an Al2O3 layer, which occurs upon exposure to oxygen. Conventionally, fluoride overcoat layers such as LiF or MgF2 have been used to solve this challenge. However, these coatings are opaque between 90 – 102 nm and generate residual absorption even above 102 nm, limiting reflectance at these short wavelengths. Furthermore, such fluoride coatings are hygroscopic and environmentally unstable. To address this issue, engineers at NASA's Goddard Space Flight Center have developed an alternative method to prevent the oxidation of Al coatings without the drawbacks associated with fluoride coatings (opaqueness, residual absorption). This NASA innovation is an Al mirror passivation process that produces a thin AlF3 overcoat layer, preventing further oxidation. The resultant AlF3 overcoat layer offers enhanced reflectivity at shorter (FUV) wavelengths compared to MgF2 and is more environmentally stable relative to LiF. Furthermore, Al mirrors receiving this innovative NASA treatment maintain 90% reflectance at longer wavelengths, enabling the development of mirrors with broadband reflectivity (e.g., from 90 – 2500 nm).