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Proceedings Paper • Open Access

Athermal metal optics made of nickel plated AlSi40
Author(s): Andreas Gebhardt; Jan Kinast; Ralf-Rainer Rohloff; Walter Seifert; Matthias Beier; Sebastian Scheiding; Thomas Peschel

Paper Abstract

Metal optics is an inherent part of space instrumentation for years. Diamond turned aluminum (Al6061) mirrors are widely used for application in the mid- and near-infrared (mid-IR and NIR, respectively) spectral range. Aluminum mirrors plated with electroless nickel (NiP) expand the field of application towards multispectral operating instruments down to the ultraviolet wavelengths. Due to the significant mismatch in the coefficient of thermal expansion (CTE) between aluminum and NiP, however, this advantage occurs at the cost of bimetallic bending. Challenging requirements can be met by using bare beryllium or aluminum beryllium composites (AlBeMet) as a CTE tailored substrate material and amorphous NiP as polishable layer. For health reasons, the use of beryllium causes complications in the process chain. Thus, the beryllium approach is subjected to specific applications only. Metal optics has proven to be advantageous in respect of using conventional CNC and ultra-precision fabrication methods to realize complex and light-weighted instrument structures. Moreover, the mirror designs can be effectively optimized for a deterministic system assembly and optimization. Limitations in terms of dimensional stability over temperature and time are mainly given by the inherent material properties (figures of merit) of the substrate material in interaction with the polishing layer.

To find an optimal compromise, a thermal matched aluminum-silicon alloy (silicon contents ≈ 40 wt%) plated with NiP (AlSi40/NiP ) was investigated in a joined project of the Max Planck Institute for Astronomy MPIA and the Fraunhofer Institute for Applied Optics and Precision Engineering IOF. The main tasks of the project were the minimization of the bimetallic bending, the development of reliable stabilizing and aging procedures, and the establishment of a proven fabrication method.

This paper describes fundamental results regarding the optimization of the athermal material combination. Furthermore, the developed production chain for high quality freeform mirrors made of AlSi40/NiP is pointed out.

Paper Details

Date Published: 17 November 2017
PDF: 9 pages
Proc. SPIE 10563, International Conference on Space Optics — ICSO 2014, 105631J (17 November 2017); doi: 10.1117/12.2304207
Show Author Affiliations
Andreas Gebhardt, Fraunhofer-Institut für Angewandte Optik und Feinmechanik (Germany)
Jan Kinast, Fraunhofer-Institut für Angewandte Optik und Feinmechanik (Germany)
Friedrich Schiller Univ. of Jena (Germany)
Ralf-Rainer Rohloff, Max-Planck-Institut für Astronomie (Germany)
Walter Seifert, Landessternwarte Heidelberg (Germany)
Matthias Beier, Fraunhofer-Institut für Angewandte Optik und Feinmechanik (Germany)
Friedrich Schiller Univ. of Jena (Germany)
Sebastian Scheiding, Astro- und Feinwerktechnik Adlershof GmbH (Germany)
Thomas Peschel, Fraunhofer-Institut für Angewandte Optik und Feinmechanik (Germany)


Published in SPIE Proceedings Vol. 10563:
International Conference on Space Optics — ICSO 2014
Zoran Sodnik; Bruno Cugny; Nikos Karafolas, Editor(s)

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