An eight-octant phase-mask coronagraph for the Subaru coronagraphic extreme AO (SCExAO) system: system design and expected performance

Details An eight-octant phase-mask coronagraph for the Subaru coronagraphic extreme AO (SCExAO) system: system design and expected performance An eight-octant phase-mask coronagraph for the Subaru coronagraphic extreme AO (SCExAO) system: system design and expected performance

Jul 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010spie.7735e.104m&link_type=abstract

Ground-based and Airborne Instrumentation for Astronomy III. Edited by McLean, Ian S.; Ramsay, Suzanne K.; Takami, Hideki. Pro

Astronomy and Astrophysics

Astronomy

1

Scientific paper

An eight-octant phase-mask (EOPM) coronagraph is one of the highest performance coronagraphic concepts, and attains simultaneously high throughput, small inner working angle, and large discovery space. However, its application to ground-based telescopes such as the Subaru Telescope is challenging due to pupil geometry (thick spider vanes and large central obstruction) and residual tip-tilt errors. We show that the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system, scheduled to be installed onto the Subaru Telescope, includes key technologies which can solve these problems. SCExAO uses a spider removal plate which translates four parts of the pupil with tilted plane parallel plates. The pupil central obstruction can be removed by a pupil remapping system similar to the PIAA optics already in the SCExAO system, which could be redesigned with no amplitude apodization. The EOPM is inserted in the focal plane to divide a stellar image into eight-octant regions, and introduces a π-phase difference between adjacent octants. This causes a self-destructive interference inside the pupil area on a following reimaged pupil plane. By using a reflective mask instead of a conventional opaque Lyot stop, the stellar light diffracted outside the pupil can be used for a coronagraphic low-order wave-front sensor to accurately measure and correct tip-tilt errors. A modified inverse-PIAA system, located behind the reimaged pupil plane, is used to remove off-axis aberrations and deliver a wide field of view. We show that this EOPM coronagraph architecture enables high contrast imaging at small working angle on the Subaru Telescope. Our approach could be generalized to other phase-mask type coronagraphs and other ground-based telescopes.

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