This article [J. Astron. Telesc. Instrum. Syst. 6(3), 035005 (Sep 24, 2020) DOI: 10.1117/1.JATIS.6.3.035005] as originally published omitted three authors as well as three references. The omitted... Show moreThis article [J. Astron. Telesc. Instrum. Syst. 6(3), 035005 (Sep 24, 2020) DOI: 10.1117/1.JATIS.6.3.035005] as originally published omitted three authors as well as three references. The omitted authors produced the Apodizing Phase Plate design used in the paper’s end-to-end simulations. This contribution was provided by David Doelman, Emiel Por, and Frans Snik, all of Leiden University. They have been added as authors on the paper, as listed above.The following acknowledgment also has been added to the published paper:“The research of DD and FS leading to these results has received funding from the European Research Council under ERC Starting Grant agreement 678194 (FALCONER).”Additionally, three references were omitted from the paper when it was published. They are listed below:61. G. Otten et al., “Performance characterization of a broadband vector Apodizing Phase Plate coronagraph,” Opt. Express 22(24), 30287 (2014).62. G. Otten et al., “The vector apodizing phase plate coronagraph: prototyping, characterization and outlook,” Proc. SPIE 9151, 91511R (2014).63. E. Por, “Optimal design of apodizing phase plate coronagraphs,” Proc. SPIE 10400, 104000V (2017).All versions of the article were corrected on 15 October 2020. The article appears correctly in print. Show less
The Magellan Extreme Adaptive Optics (MagAO-X) Instrument is an extreme AO system coming online at the end of 2019 that will be operating within the visible and near-IR. With state-of-the-art... Show moreThe Magellan Extreme Adaptive Optics (MagAO-X) Instrument is an extreme AO system coming online at the end of 2019 that will be operating within the visible and near-IR. With state-of-the-art wavefront sensing and coronagraphy, MagAO-X will be optimized for high-contrast direct exoplanet imaging at challenging visible wavelengths, particularly Hα. To enable high-contrast imaging, the instrument hosts a vector apodizing phase plate (vAPP) coronagraph. The vAPP creates a static region of high contrast next to the star that is referred to as a dark hole; on MagAO-X, the expected dark hole raw contrast is ∼4 × 10 − 6. The ability to maintain this contrast during observations, however, is limited by the presence of non-common path aberrations (NCPA) and the resulting quasi-static speckles that remain unsensed and uncorrected by the primary AO system. These quasi-static speckles within the dark hole degrade the high contrast achieved by the vAPP and dominate the light from an exoplanet. The aim of our efforts here is to demonstrate two focal plane wavefront sensing (FPWFS) techniques for sensing NCPA and suppressing quasi-static speckles in the final focal plane. To sense NCPA to which the primary AO system is blind, the science image is used as a secondary wavefront sensor. With the vAPP, a static high-contrast dark hole is created on one side of the PSF, leaving the opposite side of the PSF unocculted. In this unobscured region, referred to as the bright field, the relationship between modulations in intensity and low-amplitude pupil plane phase aberrations can be approximated as linear. The bright field can therefore be used as a linear wavefront sensor to detect small NCPA and suppress quasi-static speckles. This technique, known as spatial linear dark field control (LDFC), can monitor the bright field for aberrations that will degrade the high-contrast dark hole. A second form of FPWFS, known as holographic modal wavefront sensing (hMWFS), is also employed with the vAPP. This technique uses hologram-generated PSFs in the science image to monitor the presence of low-order aberrations. With LDFC and the hMWFS, high contrast across the dark hole can be maintained over long observations, thereby allowing planet light to remain visible above the stellar noise over the course of observations on MagAO-X. Here, we present simulations and laboratory demonstrations of both spatial LDFC and the hMWFS with a vAPP coronagraph at the University of Arizona Extreme Wavefront Control Laboratory. We show both in simulation and in the lab that the hMWFS can be used to sense low-order aberrations and reduce the wavefront error (WFE) by a factor of 3 − 4 × . We also show in simulation that, in the presence of a temporally evolving pupil plane phase aberration with 27-nm root-mean-square (RMS) WFE, LDFC can reduce the WFE to 18-nm RMS, resulting in factor of 6 to 10 gain in contrast that is kept stable over time. This performance is also verified in the lab, showing that LDFC is capable of returning the dark hole to the average contrast expected under ideal lab conditions. These results demonstrate the power of the hMWFS and spatial LDFC to improve MagAO-X’s high-contrast imaging capabilities for direct exoplanet imaging. Show less
