Wavefront sensing and control in space-based coronagraph instruments using Zernike's phase-contrast method

TL;DR

This paper demonstrates the effectiveness of a Zernike wavefront sensor in space-based coronagraph instruments, achieving picometer sensitivity and closed-loop control, crucial for future high-contrast space telescopes like HabEx and LUVOIR.

Contribution

The study experimentally validates Zernike's phase-contrast method for wavefront sensing in space telescopes, showing high sensitivity and control capabilities relevant for future missions.

Findings

ZWFS measures low- and mid-spatial frequency aberrations with 1 pm sensitivity.

Closed-loop control resolves individual deformable mirror actuators.

Predicted performance indicates ~1 hour integration for picometer sensitivity with natural starlight.

Abstract

Future space telescopes with coronagraph instruments will use a wavefront sensor (WFS) to measure and correct for phase errors and stabilize the stellar intensity in high-contrast images. The HabEx and LUVOIR mission concepts baseline a Zernike wavefront sensor (ZWFS), which uses Zernike's phase contrast method to convert phase in the pupil into intensity at the WFS detector. In preparation for these potential future missions, we experimentally demonstrate a ZWFS in a coronagraph instrument on the Decadal Survey Testbed in the High Contrast Imaging Testbed facility at NASA's Jet Propulsion Laboratory. We validate that the ZWFS can measure low- and mid-spatial frequency aberrations up to the control limit of the deformable mirror, with surface height sensitivity as small as 1 pm, using a configuration similar to the HabEx and LUVOIR concepts. Furthermore, we demonstrate closed-loop control, resolving an individual DM actuator, with residuals consistent with theoretical models. In addition, we predict the expected performance of a ZWFS on future space telescopes using natural starlight from a variety of spectral types. The most challenging scenarios require ~1 hr of integration time to achieve picometer sensitivity. This timescale may be drastically reduced by using internal or external laser sources for sensing purposes. The experimental results and theoretical predictions presented here advance the WFS technology in the context of the next generation of space telescopes with coronagraph instruments.