Spatial linear dark field control and holographic modal wavefront sensing with a vAPP coronagraph on MagAO-X

Kelsey Miller, Jared R. Males, Olivier Guyon, Laird M. Close, David Doelman, Frans Snik, Emiel Por, Michael J. Wilby, Christoph Keller, Chris Bohlman, Kyle Van Gorkom, Alexander Rodack, Justin Knight, Jennifer Lumbres, Steven Bos, Nemanja Jovanovic

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


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 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 1/44 × 10 - 6. The ability to maintain this contrast during observations, however, is limited by the presence of non-common path aberrations (NCPA) and theresulting 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 vAPPand 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 inthe 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 onone sideof the PSF, leaving the opposite side of the PSF unocculted. In this unobscured region, referred toas 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 usedas 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 lightto 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 vAPPcoronagraphat 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 ofa temporallyevolving 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 tothe average contrast expected under ideal lab conditions. These results demonstrate the powerof thehMWFS and spatial LDFC to improve MagAO-X's high-contrast imaging capabilities fordirect exoplanet imaging.

Original languageEnglish (US)
Article number049004
JournalJournal of Astronomical Telescopes, Instruments, and Systems
Issue number4
StatePublished - Oct 1 2019


  • Magellan Extreme Adaptive Optics
  • coronagraphic low-order wavefront sensing
  • direct exoplanet imaging
  • high-contrast imaging
  • holographic modal wavefront sensing
  • spatial linear dark-field control
  • vector apodizingphase plate
  • wavefront control

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Control and Systems Engineering
  • Instrumentation
  • Astronomy and Astrophysics
  • Mechanical Engineering
  • Space and Planetary Science


Dive into the research topics of 'Spatial linear dark field control and holographic modal wavefront sensing with a vAPP coronagraph on MagAO-X'. Together they form a unique fingerprint.

Cite this