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A diamond AGPM coronagraph for VISIR
Delacroix, Christian; Absil, Olivier; Mawet, Dimitri et al.
2012In McLean, I; Ramsay, S; Takami, H (Eds.) Ground-based and Airborne Instrumentation for Astronomy IV
 

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Abstract :
[en] In recent years, phase mask coronagraphy has become increasingly efficient in imaging the close environment of stars, enabling the search for exoplanets and circumstellar disks. Coronagraphs are ideally suited instruments, characterized by high dynamic range imaging capabilities, while preserving a small inner working angle. The AGPM (Annular Groove Phase Mask, Mawet et al. 20051) consists of a vector vortex induced by a rotationally symmetric subwavelength grating. This technique constitutes an almost unique solution to the achromatization at longer wavelengths (mid-infrared). For this reason, we have specially conceived a mid-infrared AGPM coronagraph for the forthcoming upgrade of VISIR, the mid-IR imager and spectrograph on the VLT at ESO (Paranal), in collaboration with members of the VISIR consortium. The implementation phase of the VISIR Upgrade Project is foreseen for May-August 2012, and the AGPM installed will cover the 11-13.2 μm spectral range. In this paper, we present the entire fabrication process of our AGPM imprinted on a diamond substrate. Diamond is an ideal material for mid-infrared wavelengths owing to its high transparency, small dispersion, extremely low thermal expansion and outstanding mechanical and chemical properties. The design process has been performed with an algorithm based on the rigorous coupled wave analysis (RCWA), and the micro-fabrication has been carried out using nano-imprint lithography and reactive ion etching. A precise grating profile metrology has also been conducted using cleaving techniques. Finally, we show the deposit of fiducials (i.e. centering marks) with Aerosol Jet Printing (AJP). We conclude with the ultimate coronagraph expected performances.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Delacroix, Christian  ;  Université de Liège - ULiège > Département de physique > Optique - Hololab
Absil, Olivier  ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Astroph. extragalactique et observations spatiales (AEOS)
Mawet, Dimitri
Hanot, Charles
Karlsson, Mikael
Forsberg, Pontus
Pantin, Eric
Surdej, Jean  ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Astroph. extragalactique et observations spatiales (AEOS)
Habraken, Serge ;  Université de Liège - ULiège > Département de physique > Optique - Hololab
Language :
English
Title :
A diamond AGPM coronagraph for VISIR
Publication date :
05 July 2012
Event name :
Ground-based and Airborne Instrumentation for Astronomy IV
Event place :
Amsterdam, Netherlands
Event date :
1 - 6 July 2012
Audience :
International
Main work title :
Ground-based and Airborne Instrumentation for Astronomy IV
Editor :
McLean, I
Ramsay, S
Takami, H
Publisher :
SPIE, Bellingham, United States - Washington
ISBN/EAN :
9780819491473
Collection name :
Proceedings of SPIE, Volume 8446
Name of the research project :
VORTEX
Available on ORBi :
since 02 March 2013

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