Polarization aberrations in next-generation Giant Segmented Mirror Telescopes (GSMTs)

II. Influence of segment-to-segment coating variations on high-contrast imaging and polarimetry

¹ Steward Observatory, University of Arizona, 933N Cherry Avenue, Tucson, AZ 85721, USA
² James C. Wyant College of Optical Sciences, University of Arizona, 933N Cherry Avenue, Tucson, AZ 85721, USA
³ Department of Physics, University of California, Santa Barbara, CA 93106, USA
⁴ Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
⁵ European Southern Observatory (ESO), Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago de Chile, Chile
⁶ TMT International Observatory LLC, 100 W. Walnut St., Suite 300, Pasadena, CA 91124, USA

^★★ Corresponding author; jarenashcraft@ucsb.edu

Received: 18 October 2024
Accepted: 6 January 2025

Abstract

Context. Direct exo-earth imaging is a key science goal for astronomy in the next decade. This ambitious task imposes a target contrast of ≈10⁻⁷ at wavelengths from I to J-band. In our prior study, we determined that polarization aberrations can limit the achievable contrast to 10⁻⁵ to 10⁻⁶ in the infrared. However, these results assumed a perfect coronagraph coupled to a telescope with an ideal coating on each of the mirrors.

Aims. In this study we seek to understand the influence of polarization aberrations from segment-to-segment coating variations on coronagraphy and polarimetry.

Methods. We use the Poke open-source polarization ray tracing package to compute the Jones pupil of each GSMT with spatially- varying coatings applied to the segments. The influence of the resultant polarization aberrations is simulated by propagating the Jones pupil through physical optics models of coronagraphs using HCIPy.

Results. After applying wavefront control from an ideal adaptive optics system, we determine that the segment-to-segment variations applied limit the performance of coronagraphy to a raw contrast of approximately 10⁻⁸ in I-band, which is 2–3 orders of magnitude lower the target performance for high-contrast imaging systems on the ground. This is a negligible addition to the nominal polarization aberrations for ground-based systems. We further observe negligible degradation in polarimetric imaging of debris disks from segment-to-segment aberrations above and beyond the impact of nominal polarization aberration.