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Spatial linear dark field control on Subaru/SCExAO. Maintaining high contrast with a vAPP coronagraph

Miller, K. L. and Bos, S. P. and Lozi, J. and Guyon, O. and Doelman, D. S. and Vievard, S. and Sahoo, A. and Deo, V. and Jovanovic, N. and Martinache, F. and Snik, F. and Currie, T. (2021) Spatial linear dark field control on Subaru/SCExAO. Maintaining high contrast with a vAPP coronagraph. Astronomy and Astrophysics, 646 . Art. No. A145. ISSN 0004-6361.

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Context. One of the key challenges facing direct exoplanet imaging is the continuous maintenance of the region of high contrast within which light from the exoplanet can be detected above the stellar noise. In high-contrast imaging systems, the dominant source of aberrations is the residual wavefront error that arises due to non-common path aberrations (NCPA) to which the primary adaptive optics (AO) system is inherently blind. Slow variations in the NCPA generate quasi-static speckles in the post-AO corrected coronagraphic image resulting in the degradation of the high-contrast dark hole created by the coronagraph. Aims. In this paper, we demonstrate spatial linear dark field control (LDFC) with an asymmetric pupil vector apodizing phase plate (APvAPP) coronagraph as a method to sense time-varying NCPA using the science image as a secondary wavefront sensor (WFS) running behind the primary AO system. By using the science image as a WFS, the NCPA to which the primary AO system is blind can be measured with high sensitivity and corrected, thereby suppressing the quasi-static speckles which corrupt the high contrast within the dark hole. Methods. On the Subaru Coronagraphic Extreme Adaptive Optics instrument (SCExAO), one of the coronagraphic modes is an APvAPP which generates two PSFs, each with a 180° D-shaped dark hole with approximately 10⁻⁴ contrast at λ = 1550 nm. The APvAPP was utilized to first remove the instrumental NCPA in the system and increase the high contrast within the dark holes. Spatial LDFC was then operated in closed-loop to maintain this high contrast in the presence of a temporally-correlated, evolving phase aberration with a root-mean-square wavefront error of 80 nm. In the tests shown here, an internal laser source was used, and the deformable mirror was used both to introduce random phase aberrations into the system and to then correct them with LDFC in closed-loop operation. Results. The results presented here demonstrate the ability of the APvAPP combined with spatial LDFC to sense aberrations in the high amplitude regime (∼80 nm). With LDFC operating in closed-loop, the dark hole is returned to its initial contrast and then maintained in the presence of a temporally-evolving phase aberration. We calculated the contrast in 1 λ/D spatial frequency bins in both open-loop and closed-loop operation, and compared the measured contrast in these two cases. This comparison shows that with LDFC operating in closed-loop, there is a factor of ∼3x improvement (approximately a half magnitude) in contrast across the full dark hole extent from 2−10 λ/D. This improvement is maintained over the full duration (10 000 iterations) of the injected temporally-correlated, evolving phase aberration. Conclusions. This work marks the first deployment of spatial LDFC on an active high-contrast imaging instrument. Our SCExAO testbed results show that the combination of the APvAPP with LDFC provides a powerful new focal plane wavefront sensing technique by which high-contrast imaging systems can maintain high contrast during long observations. This conclusion is further supported by a noise analysis of LDFC’s performance with the APvAPP in simulation.

Item Type:Article
Related URLs:
URLURL TypeDescription
Miller, K. L.0000-0003-4716-5657
Lozi, J.0000-0002-3047-1845
Guyon, O.0000-0002-1097-9908
Doelman, D. S.0000-0003-0695-0480
Vievard, S.0000-0003-4018-2569
Sahoo, A.0000-0003-2806-1254
Jovanovic, N.0000-0001-5213-6207
Martinache, F.0000-0003-1180-4138
Snik, F.0000-0003-1946-7009
Currie, T.0000-0002-7405-3119
Additional Information:© ESO 2021. Received 2 October 2020 / Accepted 18 December 2020. The research of S. P. Bos and F. Snik leading to these results has received funding from the European Research Council under ERC Starting Grant agreement 678194 (FALCONER). The development of SCExAO was supported by the Japan Society for the Promotion of Science (Grant-in-Aid for Research #23340051, #26220704, #23103002, #19H00703, and #19H00695), the Astrobiology Center of the National Institutes of Natural Sciences, Japan, the Mt Cuba Foundation and the director’s contingency fund at Subaru Telescope. LDFC development at SCExAO was supported by the NASA Strategic Astrophysics Technology (SAT) Program grant #80NSSC19K0121. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are very fortunate to have the opportunity to conduct observations from this mountain. This research made use of MATLAB as well as HCIPy, an open-source object-oriented framework written in Python for performing end-to-end simulations of high-contrast imaging instruments (Por et al. 2018). This research used the following Python libraries: Scipy (Jones et al. 2014), Numpy (Walt et al. 2011), and Matplotlib (Hunter 2007). K. L. Miller and S. P. Bos have contributed equally to this work.
Funding AgencyGrant Number
European Research Council (ERC)678194
Japan Society for the Promotion of Science (JSPS)23340051
Japan Society for the Promotion of Science (JSPS)26220704
Japan Society for the Promotion of Science (JSPS)23103002
Japan Society for the Promotion of Science (JSPS)19H00703
Japan Society for the Promotion of Science (JSPS)19H00695
Mt. Cuba Astronomical FoundationUNSPECIFIED
Subaru TelescopeUNSPECIFIED
National Institutes of Natural Sciences of JapanUNSPECIFIED
Subject Keywords:instrumentation: adaptive optics / instrumentation: high angular resolution
Record Number:CaltechAUTHORS:20210222-100903150
Persistent URL:
Official Citation:Spatial linear dark field control on Subaru/SCExAO - Maintaining high contrast with a vAPP coronagraph K. L. Miller, S. P. Bos, J. Lozi, O. Guyon, D. S. Doelman, S. Vievard, A. Sahoo, V. Deo, N. Jovanovic, F. Martinache, F. Snik and T. Currie A&A, 646 (2021) A145 DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108136
Deposited By: George Porter
Deposited On:23 Feb 2021 15:09
Last Modified:23 Feb 2021 15:09

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