Dual Purpose Lyot Coronagraph Masks for Simultaneous High-Contrast Imaging and High-Resolution Wavefront Sensing

TL;DR

This paper presents the design, manufacturing, and testing of dual-purpose Lyot coronagraph masks that enable simultaneous high-contrast imaging of exoplanets and wavefront sensing for space telescopes.

Contribution

It introduces novel dual-purpose masks combining starlight suppression and wavefront sensing, including a tiered metallic occulter and a dichroic-coated substrate, with a second-generation metasurface design.

Findings

Successful initial testing at NASA's HCIT facility.

Effective suppression of starlight with phase-shifting occulters.

Enhanced wavefront error detection using dichroic coatings.

Abstract

Directly imaging Earth-sized exoplanets with a visible-light coronagraph instrument on a space telescope will require a system that can achieve $\sim10^{-10}$ raw contrast and maintain it for the duration of observations (on the order of hours or more). We are designing, manufacturing, and testing Dual Purpose Lyot coronagraph (DPLC) masks that allow for simultaneous wavefront sensing and control using out-of-band light to maintain high contrast in the science focal plane. Our initial design uses a tiered metallic focal plane occulter to suppress starlight in the transmitted coronagraph channel and a dichroic-coated substrate to reflect out-of-band light to a wavefront sensing camera. The occulter design introduces a phase shift such that the reflected channel is a Zernike wavefront sensor. The dichroic coating allows higher-order wavefront errors to be detected which is especially critical for compensating for residual drifts from an actively-controlled segmented primary mirror. A second-generation design concept includes a metasurface to create polarization-dependent phase shifts in the reflected beam, which has several advantages including an extended dynamic range. We will present the focal plane mask designs, characterization, and initial testing at NASA's High Contrast Imaging Testbed (HCIT) facility.