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Proceedings Paper

Development of high reflectivity coatings for large format Fabry-Perot etalons
Author(s): M. Sigwarth; J. Baumgartner; A. Bell; G. Cagnoli; A. Fischer; C. Halbgewachs; F. Heidecke; Th. J. Kentischer; B. Kestner; P. Kuschnir; O. von der Lühe; L. Pinard; Ch. Michel; W. J. Reichman; B. Sassolas; Th. Scheiffelen; W. Schmidt
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Paper Abstract

The Visible Tunable Filter (VTF) is a diffraction-limited narrowband tunable instrument for imaging spectropolarimetry in the wavelength range between 520 and 860 nm. It is based on large-format Fabry Perot. The instrument will be one of the first-light instruments of the 4m aperture Daniel K. Inoue Solar Telescope (DKIST). To provide a field of view of 1 arcmin and a spectral resolution λ/Δλ of about 100.000, the required free aperture of the Fabry Perot is 250mm. The high reflectivity coatings for the Etalon plates need to meet the specifications for the reflectivity over the entire wavelength range and preserve the plate figure specifications of better λ/300, and a micro roughness of < 0.4 nm rms. Coated surfaces with similar specifications have successfully been made for reflecting mirrors on thick substrates but not for larger format Fabry-Perot systems. Ion Beam Sputtering (IBS) based coatings provide stable, homogeneous, and smooth coatings. But IBS coatings also introduce stresses to the substrate that influence the plate figure in our case at the nm level. In a joint effort with an industry partner and a French CNRS research laboratory, we developed and tested processes on small and full size substrates, to provide coated Etalon plates to the required specifications. Zygo Extreme Precision Optics, Richmond, CA, USA, is polishing and figuring the substrates, doing the metrology and FE analysis. LMA (Laboratoire Matériaux Avancés, Lyon, France) is designing and making the IBS coatings and investigating the detailed behavior of the coatings and related processes. Both partners provide experience from manufacturing coated plane optics for gravitational wave detection experiments and EUV optics. The Kiepenheuer-Institut für Sonnenphysik, Freiburg, Germany is designing and building the VTF instrument and is leading the coating development. We present the characteristics of the coatings and the substrate processing concept, as well as results from tests on sample size and from full size substrate processing. We demonstrate that the tight specifications for a single Etalon can be reached.

Paper Details

Date Published: 9 August 2016
PDF: 14 pages
Proc. SPIE 9908, Ground-based and Airborne Instrumentation for Astronomy VI, 99084F (9 August 2016); doi: 10.1117/12.2232271
Show Author Affiliations
M. Sigwarth, Kiepenheuer-Institut für Sonnenphysik (Germany)
J. Baumgartner, Kiepenheuer-Institut für Sonnenphysik (Germany)
A. Bell, Kiepenheuer-Institut für Sonnenphysik (Germany)
G. Cagnoli, IN2P3-Lab. des Matériaux Avancés, CNRS (France)
Univ. Claude Bernard Lyon (France)
A. Fischer, Kiepenheuer-Institut für Sonnenphysik (Germany)
C. Halbgewachs, Kiepenheuer-Institut für Sonnenphysik (Germany)
F. Heidecke, Kiepenheuer-Institut für Sonnenphysik (Germany)
Th. J. Kentischer, Kiepenheuer-Institut für Sonnenphysik (Germany)
B. Kestner, Zygo Extreme Precision Optics (United States)
P. Kuschnir, Zygo Extreme Precision Optics (United States)
O. von der Lühe, Kiepenheuer-Institut für Sonnenphysik (Germany)
L. Pinard, IN2P3-Lab. des Matériaux Avancés, CNRS (France)
Ch. Michel, IN2P3-Lab. des Matériaux Avancés, CNRS (France)
W. J. Reichman, Zygo Extreme Precision Optics (United States)
B. Sassolas, IN2P3-Lab. des Matériaux Avancés, CNRS (France)
Th. Scheiffelen, Kiepenheuer-Institut für Sonnenphysik (Germany)
W. Schmidt, Kiepenheuer-Institut für Sonnenphysik (Germany)

Published in SPIE Proceedings Vol. 9908:
Ground-based and Airborne Instrumentation for Astronomy VI
Christopher J. Evans; Luc Simard; Hideki Takami, Editor(s)

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