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Development of a subwavelength grating vortex coronagraph of topological charge 4 (SGVC4)

Delacroix, Christian and Absil, Olivier and Carlomagno, Brunella and Piron, Pierre and Forsberg, Pontus and Karlsson, Mikael and Mawet, Dimitri and Habraken, Serge and Surdej, Jean (2014) Development of a subwavelength grating vortex coronagraph of topological charge 4 (SGVC4). In: Ground-based and Airborne Instrumentation for Astronomy V. Proceedings of SPIE. No.9147. Society of Photo-Optical Instrumentation Engineers (SPIE) , Bellingham, WA, Art. No. 91478Y. ISBN 9780819496157.

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One possible solution to achieve high contrast direct imaging at a small inner working angle (IWA) is to use a vector vortex coronagraph (VVC), which provides a continuous helical phase ramp in the focal plane of the telescope with a phase singularity in its center. Such an optical vortex is characterized by its topological charge, i.e., the number of times the phase accumulates 2π radians along a closed path surrounding the singularity. Over the past few years, we have been developing a charge-2 VVC induced by rotationally symmetric subwavelength gratings (SGVC2), also known as the Annular Groove Phase Mask (AGPM). Since 2013, several SGVC2s (or AGPMs) were manufactured using synthetic diamond substrate, then validated on dedicated optical benches, and installed on 10-m class telescopes. Increasing the topological charge seems however mandatory for cancelling the light of bright stars which will be partially resolved by future Extremely Large Telescopes in the near-infrared. In this paper, we first detail our motivations for developing an SGVC4 (charge 4) dedicated to the near-infrared domain. The challenge lies in the design of the pattern which is unrealistic in the theoretically perfect case, due to state-of-the-art manufacturing limitations. Hence, we propose a new realistic design of SGVC4 with minimized discontinuities and optimized phase ramp, showing conclusive improvements over previous works in this field. A preliminary validation of our concept is given based on RCWA simulations, while full 3D finite-difference time-domain simulations (and eventually laboratory tests) will be required for a final validation.

Item Type:Book Section
Related URLs:
URLURL TypeDescription Paper
Absil, Olivier0000-0002-4006-6237
Karlsson, Mikael0000-0002-2011-0851
Mawet, Dimitri0000-0002-8895-4735
Surdej, Jean0000-0002-7005-1976
Additional Information:© 2014 Society of Photo-Optical Instrumentation Engineers (SPIE). The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (ERC Grant Agreement n.337569) and from the French Community of Belgium through an ARC grant for Concerted Research Actions.
Funding AgencyGrant Number
European Research Council (ERC)337569
Communauté française de Belgique – Actions de recherche concertées – Académie universitaire Wallonie-EuropeUNSPECIFIED
Subject Keywords:extrasolar planet, vector vortex coronagraphy, phase mask, subwavelength grating, high contrast imaging, small inner working angle
Series Name:Proceedings of SPIE
Issue or Number:9147
Record Number:CaltechAUTHORS:20150520-081847128
Persistent URL:
Official Citation:Christian Delacroix ; Olivier Absil ; Brunella Carlomagno ; Pierre Piron ; Pontus Forsberg ; Mikael Karlsson ; Dimitri Mawet ; Serge Habraken and Jean Surdej " Development of a subwavelength grating vortex coronagraph of topological charge 4 (SGVC4) ", Proc. SPIE 9147, Ground-based and Airborne Instrumentation for Astronomy V, 91478Y (July 8, 2014); doi:10.1117/12.2055798;
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:57684
Deposited By: Ruth Sustaita
Deposited On:20 May 2015 16:06
Last Modified:10 Nov 2021 21:53

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