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Proceedings Paper

Annular groove phase mask coronagraph in diamond for mid-IR wavelengths: manufacturing assessment and performance analysis
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Paper Abstract

Phase-mask coronagraphs are known to provide high contrast imaging capabilities while preserving a small inner working angle, which allows searching for exoplanets or circumstellar disks with smaller telescopes or at longer wavelengths. The AGPM (Annular Groove Phase Mask, Mawet et al. 20051) is an optical vectorial vortex coronagraph (or vector vortex) induced by a rotationally symmetric subwavelength grating (i.e. with a period smaller than λ/n, λ being the observed wavelength and n the refractive index of the grating substrate). In this paper, we present our first midinfrared AGPM prototypes imprinted on a diamond substrate. We firstly give an extrapolation of the expected coronagraph performances in the N-band (~10 μm), and prospects for down-scaling the technology to the most wanted L-band (~3.5 μm). We then present the manufacturing and measurement results, using diamond-optimized microfabrication techniques such as nano-imprint lithography (NIL) and reactive ion etching (RIE). Finally, the subwavelength grating profile metrology combines surface metrology (scanning electron microscopy, atomic force microscopy, white light interferometry) with diffractometry on an optical polarimetric bench and cross correlation with theoretical simulations using rigorous coupled wave analysis (RCWA).

Paper Details

Date Published: 10 August 2010
PDF: 10 pages
Proc. SPIE 7731, Space Telescopes and Instrumentation 2010: Optical, Infrared, and Millimeter Wave, 77314W (10 August 2010);
Show Author Affiliations
C. Delacroix, Univ. de Liège (Belgium)
P. Forsberg, Uppsala Univ. (Sweden)
M. Karlsson, Uppsala Univ. (Sweden)
D. Mawet, Jet Propulsion Lab. (United States)
C. Lenaerts, Ctr. Spatial de Liège (Belgium)
S. Habraken, Univ. de Liège (Belgium)
Ctr. Spatial de Liège (Belgium)
C. Hanot, Univ. de Liège (Belgium)
J. Surdej, Univ. de Liège (Belgium)
A. Boccaletti, Observatoire de Paris à Meudon (France)
J. Baudrand, Observatoire de Paris à Meudon (France)

Published in SPIE Proceedings Vol. 7731:
Space Telescopes and Instrumentation 2010: Optical, Infrared, and Millimeter Wave
Jacobus M. Oschmann Jr.; Mark C. Clampin; Howard A. MacEwen, Editor(s)

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