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Stray light reduction of silicon particle reinforced aluminum for optical systems

: Kinast, J.; Telle, A.; Schröder, S.; Trost, M.; Risse, S.


Sodnik, Z. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
International Conference on Space Optics, ICSO 2018 : Chania, Greece, 9-12 October 2018
Bellingham, WA: SPIE, 2019 (Proceedings of SPIE 11180)
ISBN: 978-1-5106-3077-2
Paper 111802G, 8 S.
International Conference on Space Optics (ICSO) <12, 2018, Chania>
Fraunhofer IOF ()

Silicon particle reinforced aluminum containing 42 wt.% silicon (Al-42Si) offers higher specific stiffness, higher resistance to thermal gradients, and an athermal behavior combined with electroless nickel, in comparison to state-of-the-art aluminum alloys (e.g. Al6061). Nevertheless, typical surface modifications (e.g. black anodization) lead to a nonsufficient optical stray light suppression due to the high amount of silicon particles on the surface. Therefore, a coating technique is required that fulfils the optical and the mechanical (e.g. adhesive strength) specifications for stray light reduction on Al-42Si. Different components like housings and barrels made of Al-42Si were coated with amorphous NiP and with Fractal Black™ by Acktar Ltd. The optical performance is analyzed by angle-resolved light scattering (ARS) at two different wavelengths (532 nm and 1064 nm). Fractal Black™ offers a total scattering level of lower than 2 % at 532 nm and 1064 nm. Fractal Black™ has been proven as a suitable coating for components made of Al-42Si.