Development of an aluminium mirror with a novel integrated flexure-based mount for METIS cryogenic environment

Daan Zaalberg; Mirka Lewińska-Maresca; Erik Ruinemans; Niels Tromp; Dennis Dolkens; Tibor Agocs; Jeff Lynn; Ivan Lloro; Menno Schuil; Menno de Haan; Rik ter Horst; Eddy Elswijk

doi:10.1117/12.2629995

29 August 2022 Development of an aluminium mirror with a novel integrated flexure-based mount for METIS cryogenic environment

Daan Zaalberg, Mirka Lewińska-Maresca, Erik Ruinemans, Niels Tromp, Dennis Dolkens, Tibor Agocs, Jeff Lynn, Ivan Lloro, Menno Schuil, Menno de Haan, Rik ter Horst, Eddy Elswijk

Author Affiliations +

Proceedings Volume 12188, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation V; 121881O (2022) https://doi.org/10.1117/12.2629995
Event: SPIE Astronomical Telescopes + Instrumentation, 2022, Montréal, Québec, Canada

Abstract

The development of the optical components for METIS, which is the mid-infrared ELT imager and spectrograph, is a challenging task. On one hand, there are tight requirements regarding wavefront error, driven mostly by high contrast imaging modes. On the other hand, limited space envelopes are available. In this paper, we present the development of the largest flat aluminium mirror of derotator mechanism which is located within the Common Fore Optics (CFO) of METIS. The 240mm-diameter mirror is made of gold coated Rapidly Solidified Aluminium (RSA) 6061-T6 with the compact flexure-based mount directly embedded in the mirror body. This novel design includes mounting pads that are located at the front, inside the optical surface. This approach improves the universality of the proposed solution while introducing challenges from the manufacturing point of view, i.e. surface holes that make polishing more difficult. The mount design is a combination of leaf springs and rotational hinges and is optimised to reduce the aberrations due to gravity and assembly loads. Thanks to the in-house manufacturing process relying on 5-axes milling capabilities, it is possible to create such a complex integrated mirror mount with minimal impact of the holes on the quality of the optical surface. Numerical simulations of this mirror performed for various load cases contributing to surface aberrations show extremely low surface form error (< 15 nm RMS) of the metallic mirror.

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Daan Zaalberg, Mirka Lewińska-Maresca, Erik Ruinemans, Niels Tromp, Dennis Dolkens, Tibor Agocs, Jeff Lynn, Ivan Lloro, Menno Schuil, Menno de Haan, Rik ter Horst, and Eddy Elswijk "Development of an aluminium mirror with a novel integrated flexure-based mount for METIS cryogenic environment", Proc. SPIE 12188, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation V, 121881O (29 August 2022); https://doi.org/10.1117/12.2629995

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