11 July 2016 Development of low-stress Iridium coatings for astronomical x-ray mirrors
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Abstract
Previously used mirror technologies are not suitable for the challenging needs of future X-ray telescopes. This is why the required high precision mirror manufacturing triggers new technical developments around the world. Some aspects of X-ray mirrors production are studied within the interdisciplinary project INTRAAST, a German acronym for "industry transfer of astronomical mirror technologies". The project is embedded in a cooperation of Aschaffenburg University of Applied Sciences and the Max-Planck-Institute for extraterrestrial Physics. One important task is the development of low-stress Iridium coatings for X-ray mirrors based on slumped thin glass substrates. The surface figure of the glass substrates is measured before and after the coating process by optical methods. Correlating the surface shape deformation to the parameters of coating deposition, here especially to the Argon sputtering pressure, allows for an optimization of the process. The sputtering parameters also have an influence on the coating layer density and on the micro-roughness of the coatings, influencing their X-ray reflection properties. Unfortunately the optimum coating process parameters seem to be contrarious: low Argon pressure resulted in better micro-roughness and higher density, whereas higher pressure leads to lower coating stress. Therefore additional measures like intermediate coating layers and temperature treatment will be considered for further optimization. The technical approach for the low-stress Iridium coating development, the experimental equipment, and the obtained first experimental results are presented within this paper.
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Thorsten Döhring, Anne-Catherine Probst, Manfred Stollenwerk, Mingwu Wen, Laura Proserpio, "Development of low-stress Iridium coatings for astronomical x-ray mirrors", Proc. SPIE 9905, Space Telescopes and Instrumentation 2016: Ultraviolet to Gamma Ray, 99056V (11 July 2016); doi: 10.1117/12.2232074; https://doi.org/10.1117/12.2232074
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