Making the unmodulated Pyramid wavefront sensor smart. Closed-loop demonstration of neural network wavefront reconstruction with MagAO-X

arXiv (Cornell University)

Abstract

Almost all current and future high-contrast imaging instruments will use a Pyramid wavefront sensor (PWFS) as a primary or secondary wavefront sensor. The main issue with the PWFS is its nonlinear response to large phase aberrations, especially under strong atmospheric turbulence. Most instruments try to increase its linearity range by using dynamic modulation, but this leads to decreased sensitivity, most prominently for low-order modes, and makes it blind to petal-piston modes. In the push toward high-contrast imaging of fainter stars and deeper contrasts, there is a strong interest in using the PWFS in its unmodulated form. Here, we present closed-loop lab results of a nonlinear reconstructor for the unmodulated PWFS of the Magellan Adaptive Optics eXtreme (MagAO-X) system based on convolutional neural networks (CNNs). We show that our nonlinear reconstructor has a dynamic range of >600 nm root-mean-square (RMS), significantly outperforming the linear reconstructor that only has a 50 nm RMS dynamic range. The reconstructor behaves well in closed loop and can obtain >80% Strehl at 875 nm under a large variety of conditions and reaches higher Strehl ratios than the linear reconstructor under all simulated conditions. The CNN reconstructor also achieves the theoretical sensitivity limit of a PWFS, showing that it does not lose its sensitivity in exchange for dynamic range. The current CNN's computational time is 690 microseconds, which enables loop speeds of >1 kHz. On-sky tests are foreseen soon and will be important for pushing future high-contrast imaging instruments toward their limits.

Authors 15

1. Rico Landman Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory , Leiden University , PO Box 9513 , 2300 RA Leiden , The Netherlands

2. Sebastiaan Y. Haffert

   University of Arizona

   Affiliation as printed

   Steward Observatory , The Unversity of Arizona , 933 North Cherry Avenue , Tucson , Arizona

3. Jared R. Males

   University of Arizona

   Affiliation as printed

   Steward Observatory , The Unversity of Arizona , 933 North Cherry Avenue , Tucson , Arizona

4. Laird M. Close

   University of Arizona

   Affiliation as printed

   Steward Observatory , The Unversity of Arizona , 933 North Cherry Avenue , Tucson , Arizona

5. Warren B. Foster

   University of Arizona

   Affiliation as printed

   Steward Observatory , The Unversity of Arizona , 933 North Cherry Avenue , Tucson , Arizona

6. Kyle Van Gorkom

   University of Arizona

   Affiliation as printed

   Steward Observatory , The Unversity of Arizona , 933 North Cherry Avenue , Tucson , Arizona

7. Olivier Guyon
8. Alexander D. Hedglen
   Affiliation as printed

   Northrop Grumman Corporation , 600 South Hicks Road , Rolling Meadows , Illinois

9. Maggie Kautz

   University of Arizona

   Affiliation as printed

   Wyant College of Optical Sciences , The University of Arizona , 1630 E University Blvd , Tucson , Arizona

10. Jay K. Kueny

    University of Arizona

    Affiliation as printed

    Wyant College of Optical Sciences , The University of Arizona , 1630 E University Blvd , Tucson , Arizona

11. Joseph D. Long

    Flatiron Institute

    Affiliation as printed

    Center for Computational Astrophysics , Flatiron Institute , 162 5th Avenue , New York , New York

12. Jennifer Lumbres

    University of Arizona

    Affiliation as printed

    Wyant College of Optical Sciences , The University of Arizona , 1630 E University Blvd , Tucson , Arizona

13. Eden McEwen

    University of Arizona

    Affiliation as printed

    Wyant College of Optical Sciences , The University of Arizona , 1630 E University Blvd , Tucson , Arizona

14. A. McLeod

    Draper Laboratory

    Affiliation as printed

    Draper Laboratory , 555 Technology Square , Cambridge , Massachusetts

15. Lauren Schatz

    Kirtland Air Force Base

    Affiliation as printed

    Starfire Optical Range , Kirtland Air Force Base , Albuquerque , New Mexico