Prototyping liquid-crystal coronagraphs for exo-Earth imaging

TL;DR

This paper reports on the development and initial testing of liquid-crystal vector vortex coronagraphs designed to achieve extremely high contrast for direct imaging of Earth-like exoplanets, addressing polarization leakage issues.

Contribution

It introduces multi-grating liquid-crystal VVCs with improved polarization leakage reduction and details calibration techniques to enhance manufacturing accuracy.

Findings

Achieved polarization leakage reduction to 10^-10 contrast level.

Developed calibration methods using polarization microscopes and Mueller matrix ellipsometers.

Prepared for performance testing on a high-contrast imaging testbed.

Abstract

This paper presents initial results from the ESA-funded ``SUPPPPRESS'' project, which aims to develop high-performance liquid-crystal coronagraphs for direct imaging of Earth-like exoplanets in reflected light. The project focuses on addressing the significant challenge of polarization leakage in vector vortex coronagraphs (VVCs). We utilize newly manufactured multi-grating, liquid-crystal VVCs, consisting of a two- or three-element stack of vortex and grating patterns, to reduce this leakage to the $10^{-10}$ contrast level. We detail the experimental setups, including calibration techniques with polarization microscopes and Mueller matrix ellipsometers to enhance the direct-write accuracy of the liquid-crystal patterns. The performance testing of these coronagraph masks will be conducted on the THD2 high-contrast imaging testbed in Paris.