An Eight-Octant Phase-Mask Coronagraph

TL;DR

This paper introduces an eight-octant phase-mask coronagraph that improves contrast and tolerance to errors over traditional designs, with promising laboratory and simulation results for high-contrast imaging.

Contribution

It presents the design, simulation, and experimental validation of an eight-octant phase-mask coronagraph with enhanced performance features.

Findings

Achievable contrast is significantly improved compared to four-quadrant designs.

The EOPM has higher optical throughput and smaller inner working angle.

Laboratory tests show better tip-tilt error tolerance.

Abstract

We present numerical simulations and laboratory experiments on an eight-octant phase-mask (EOPM) coronagraph. The numerical simulations suggest that an achievable contrast for the EOPM coronagraph can be greatly improved as compared to that of a four-quadrant phase-mask (FQPM) coronagraph for a partially resolved star. On-sky transmission maps reveal that the EOPM coronagraph has relatively high optical throughput, a small inner working angle and large discovery space. We have manufactured an eight-segment phase mask utilizing a nematic liquid-crystal device, which can be easily switched between the FQPM and the EOPM modes. The laboratory experiments demonstrate that the EOPM coronagraph has a better tolerance of the tip-tilt error than the FQPM one. We also discuss feasibility of a fully achromatic and high-throughput EOPM coronagraph utilizing a polarization interferometric technique.