Gratis Mitigation of Polarization Aberration Effects in Coronagraphic Dark Holes

Abstract

Direct imaging of exoplanets requires stellar coronagraphs capable of suppressing starlight to contrast levels below $10^{-8}$. Active wavefront control with deformable mirrors (DMs) is essential to create dark holes in the image plane. However, polarization aberrations arising from beam reduction optics and the coronagraph itself produces multiple non-interfering intensity components that have correlated responses to the DM. This article introduces the concept of gratis mitigation: when a control loop minimizes one intensity component, others can be reduced concomitantly due to the correlated DM responses. Using end-to-end physical optics simulations of a Lyot coronagraph fed by a 4 m-class telescope with $f/5$ beam reduction, we demonstrate gratis mitigation and analyze its origin via a Jones matrix formalism. Gratis mitigation has significant implications for coronagraph design, calibration, and possibly wavefront control.