Influence of evaporation rate and chamber pressure on the FUV reflectance and physical characteristics of aluminum films

Manuel A. Quijada; Javier G. Del Hoyo; Emrold Gray; J. Grabriel Richardson; Andrew Howe; Luis Rodriguez de Marcos; David A. Sheikh

doi:10.1117/12.2595392

20 August 2021 Influence of evaporation rate and chamber pressure on the FUV reflectance and physical characteristics of aluminum films

Manuel A. Quijada, Javier G. Del Hoyo, Emrold Gray, J. Grabriel Richardson, Andrew Howe, Luis Rodriguez de Marcos, David A. Sheikh

Author Affiliations +

Proceedings Volume 11819, UV/Optical/IR Space Telescopes and Instruments: Innovative Technologies and Concepts X; 118190G (2021) https://doi.org/10.1117/12.2595392
Event: SPIE Optical Engineering + Applications, 2021, San Diego, California, United States

Abstract

Space telescopes for studying astrophysical phenomena from the far ultraviolet (FUV) to the near infrared (NIR) require durable mirror coatings with high and uniform reflectance over a very broad spectral region. While coatings for the optical and NIR region are well developed with proven performance, the FUV band presents significant challenges, particularly below 115 nm. Recent developments in physical vapor deposition (PVD) coating processes of aluminum mirrors that are protected with a metal-fluoride overcoat to prevent oxidation (such as LiF, MgF₂, or AlF₃) have improved reflectance in the FUV. While the emphasis in these studies has been placed on improving the deposition conditions of the metal-fluoride overcoats, less attention has been devoted to how deposition parameters (such as vacuum conditions or deposition rates) may affect the quality of the aluminum mirrors. This paper presents characterization of Al+MgF₂ coupons made by ash evaporation of aluminum followed by resistive evaporation of MgF₂. Samples were manufactured under a variety of processing conditions and the relationship between processing variables and mirror FUV re ectivity is analyzed. Performance characterization was based on the measured near-normal reflectance in the FUV (90-180 nm), and normal-incidence transmittance in the visible was done to analyze the possible presence of pinholes in the mirror. We demonstrated pinhole-free Al/MgF₂ mirrors deposited at room temperature with a reflectivity of 0.91 at 122 nm wavelength. This reflectivity enhancement was achieved solely through parameter optimization.

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Manuel A. Quijada, Javier G. Del Hoyo, Emrold Gray, J. Grabriel Richardson, Andrew Howe, Luis Rodriguez de Marcos, and David A. Sheikh "Influence of evaporation rate and chamber pressure on the FUV reflectance and physical characteristics of aluminum films", Proc. SPIE 11819, UV/Optical/IR Space Telescopes and Instruments: Innovative Technologies and Concepts X, 118190G (20 August 2021); https://doi.org/10.1117/12.2595392

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