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Proceedings Paper

Development of a 2D precision cryogenic chopper for METIS
Author(s): Sander L. Paalvast; Huub Janssen; Maurice Teuwen; Robert Huisman; Bernhard Brandl; Frank Molster; Lars Venema
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Paper Abstract

The Mid-infrared E-ELT Imager and Spectrograph, or METIS, is foreseen as the third instrument for the European Extremely Large Telescope (E-ELT). A key part of METIS is the Cold Chopper (MCC) which switches the optical beam between the target and a nearby reference sky during observation for elimination of the fluctuating IR background signal in post-processing. This paper discusses the development of the MCC demonstrator. The chopper mirror (Ø64mm) has to tip/tilt in 2D with a combined angle of up to 13.6mrad with 1.7μrad stability and repeatability within 5ms (95% duty cycle at 5Hz) at 80K. As these requirements cannot be met in the presence of friction or backlash, the mirror is guided by a monolithically integrated flexure mechanism. The angular position is actuated by three linear actuators and measured by three linear position sensors, resulting in a fast tip, tilt, and focus mirror. Using the third actuator to introduce symmetry, homogeneity in forces and heat flux is obtained. Both the actuators and the sensors are key components. A voice coil actuator had to be custom designed, to achieve the required acceleration force within the specified 1W heat load. The requirements for the displacement measurement can be met with a commercially available, fiber interferometry system. For integration of this system, stray light elimination is a critical design aspect and retro-reflectors have been used to reflect sufficient power into the fiber at large tip/tilt angles.

Paper Details

Date Published: 13 September 2012
PDF: 6 pages
Proc. SPIE 8450, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation II, 845020 (13 September 2012); doi: 10.1117/12.925338
Show Author Affiliations
Sander L. Paalvast, Janssen Precision Engineering B.V. (Netherlands)
Huub Janssen, Janssen Precision Engineering B.V. (Netherlands)
Maurice Teuwen, Janssen Precision Engineering B.V. (Netherlands)
Robert Huisman, SRON Netherlands Institute for Space Research (Netherlands)
Bernhard Brandl, Leiden Observatory, Leiden Univ. (Netherlands)
Frank Molster, NOVA (Netherlands)
Lars Venema, ASTRON (Netherlands)

Published in SPIE Proceedings Vol. 8450:
Modern Technologies in Space- and Ground-based Telescopes and Instrumentation II
Ramón Navarro; Colin R. Cunningham; Eric Prieto, Editor(s)

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