
Proceedings Paper
Development of a subwavelength grating vortex coronagraph of topological charge 4 (SGVC4)Format | Member Price | Non-Member Price |
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Paper Abstract
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.
Paper Details
Date Published: 28 July 2014
PDF: 9 pages
Proc. SPIE 9147, Ground-based and Airborne Instrumentation for Astronomy V, 91478Y (28 July 2014); doi: 10.1117/12.2055798
Published in SPIE Proceedings Vol. 9147:
Ground-based and Airborne Instrumentation for Astronomy V
Suzanne K. Ramsay; Ian S. McLean; Hideki Takami, Editor(s)
PDF: 9 pages
Proc. SPIE 9147, Ground-based and Airborne Instrumentation for Astronomy V, 91478Y (28 July 2014); doi: 10.1117/12.2055798
Show Author Affiliations
Christian Delacroix, Univ. de Liège (Belgium)
Olivier Absil, Univ. de Liège (Belgium)
Brunella Carlomagno, Univ. de Liège (Belgium)
Pierre Piron, Univ. de Liège (Belgium)
Pontus Forsberg, Uppsala Univ. (Sweden)
Olivier Absil, Univ. de Liège (Belgium)
Brunella Carlomagno, Univ. de Liège (Belgium)
Pierre Piron, Univ. de Liège (Belgium)
Pontus Forsberg, Uppsala Univ. (Sweden)
Mikael Karlsson, Uppsala Univ. (Sweden)
Dimitri Mawet, European Southern Observatory (Chile)
Serge Habraken, Univ. de Liège (Belgium)
Jean Surdej, Univ. de Liège (Belgium)
Dimitri Mawet, European Southern Observatory (Chile)
Serge Habraken, Univ. de Liège (Belgium)
Jean Surdej, Univ. de Liège (Belgium)
Published in SPIE Proceedings Vol. 9147:
Ground-based and Airborne Instrumentation for Astronomy V
Suzanne K. Ramsay; Ian S. McLean; Hideki Takami, Editor(s)
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