Phase-Induced Amplitude Apodization on centrally obscured pupils: design and first laboratory demonstration for the Subaru Telescope pupil

TL;DR

This paper demonstrates a novel high-efficiency PIAA coronagraph design tailored for the Subaru Telescope's obscured pupil, enabling high-contrast imaging close to the diffraction limit with validated laboratory results.

Contribution

First laboratory demonstration of a PIAA-type coronagraph with pupil apodization and spider vane removal for the Subaru Telescope, validating its effectiveness for high-contrast imaging.

Findings

Achieved high contrast imaging at approximately 1 λ/D

Successfully removed central obstruction and spider vanes

Inverse PIAA system recovers wide field of view

Abstract

High contrast coronagraphic imaging is challenging for telescopes with central obstructions and thick spider vanes, such as the Subaru Telescope. We present in this paper the first laboratory demonstration of a high efficiency PIAA-type coronagraph on such a pupil, using coronagraphic optics which will be part of the Subaru Coronagraphic Extreme-AO (SCExAO) system currently under assembly. Lossless pupil apodization is performed by a set of aspheric PIAA lenses specifically designed to also remove the pupil's central obstruction, coupled with a Spider Removal Plate (SRP) which removes spider vanes by translating four parts of the pupil with tilted plane-parallel plates. An "inverse-PIAA" system, located after the coronagraphic focal plane mask, is used to remove off-axis aberrations and deliver a wide field of view. Our results validate the concept adopted for the SCExAO system, and show that the Subaru Telescope pupil can properly be apodized for high contrast coronagraphic imaging as close as $\approx$ 1 $\lambda/D$ with no loss of sensitivity. We also verify that off-axis aberrations in the system are in agreement with theory, and that the inverse PIAA system recovers a wide usable field of view for exoplanet detection and disks imaging.