The space coronagraph optical bench (SCoOB): 3. Mueller matrix polarimetry of a coronagraphic exit pupil

TL;DR

This paper presents a method to directly measure and characterize polarization aberrations in a high-contrast coronagraphic instrument using Mueller matrix polarimetry, aiding in improved exoplanet imaging.

Contribution

The study introduces a dual-rotating-retarder polarimeter to measure the Mueller matrix of the SCoOB testbed, revealing polarization aberrations at the instrument level.

Findings

Measured polarization aberrations across the exit pupil.

Quantified diattenuation, retardance, and depolarization effects.

Identified how polarization couples into imaging residuals.

Abstract

High-contrast imaging in the next decade aims to image exoplanets at smaller angular separations and deeper contrasts than ever before. A problem that has recently garnered attention for telescopes equipped with high-contrast coronagraphs is polarization aberration arising from the optics. These aberrations manifest as low-order aberrations of different magnitudes for orthogonal polarization states and spread light into the dark hole of the coronagraph that cannot be fully corrected. The origin of polarization aberrations has been modeled at the telescope level. However, we don't fully understand how polarization aberrations arise at the instrument level. To directly measure this effect, we construct a dual-rotating-retarder polarimeter around the SCoOB high-contrast imaging testbed to measure its Mueller matrix. With this matrix, we directly characterize the diattenuation, retardance, and depolarization of the instrument as a function of position in the exit pupil. We measure the polarization aberrations in the Lyot plane to understand how polarization couples into high-contrast imaging residuals.