Phase-shifting coronagraph

TL;DR

This paper explores the use of phase-shifting coronagraphs as wavefront sensors to improve star light suppression in exoplanet imaging, analyzing two implementation methods through simulations.

Contribution

It introduces and compares two phase-shifting methods for coronagraphic wavefront sensing, demonstrating their potential for enhanced star extinction control.

Findings

Image plane implementation is more efficient.

Compatible with four-quadrant and vortex phase masks.

Numerical simulations optimize performance and limitations.

Abstract

With the recent commissioning of ground instruments such as SPHERE or GPI and future space observatories like WFIRST-AFTA, coronagraphy should probably become the most efficient tool for identifying and characterizing extra-solar planets in the forthcoming years. Coronagraphic instruments such as Phase mask coronagraphs (PMC) are usually based on a phase mask or plate located at the telescope focal plane, spreading the starlight outside the diameter of a Lyot stop that blocks it. In this communication is investigated the capability of a PMC to act as a phase-shifting wavefront sensor for better control of the achieved star extinction ratio in presence of the coronagraphic mask. We discuss the two main implementations of the phase-shifting process, either introducing phase-shifts in a pupil plane and sensing intensity variations in an image plane, or reciprocally. Conceptual optical designs are described in both cases. Numerical simulations allow for better understanding of the performance and limitations of both options, and optimizing their fundamental parameters. In particular, they demonstrate that the phase-shifting process is a bit more efficient when implemented into an image plane, and is compatible with the most popular phase masks currently employed, i.e. four-quadrants and vortex phase masks.