Zernike amplitude pupil apodization for vortex coronagraphy with obscured apertures

TL;DR

This paper introduces Zernike polynomial-based pupil apodization functions for vortex coronagraphs, improving starlight suppression in telescopes with obscured apertures, especially for large ground-based telescopes like the E-ELT.

Contribution

The paper presents a novel analytical method using Zernike polynomials for pupil apodization in vortex coronagraphs, tailored for obscured telescope apertures.

Findings

Effective starlight cancellation with Zernike-based apodization.

Enhanced contrast and throughput for telescopes with central obscurations.

Suitable for large telescopes with complex aperture structures.

Abstract

A set of pupil apodization functions for use with a vortex coronagraph on telescopes with obscured apertures is presented. We show analytically that pupil amplitudes given by real-valued Zernike polynomials offer ideal on-axis starlight cancellation when applied to unobscured circular apertures. The charge of the vortex phase element must be a nonzero even integer, greater than the sum of the degree and the absolute value of its azimuthal order of the Zernike polynomial. Zero-valued lines and points of Zernike polynomials, or linear combinations thereof, can be matched to obstructions in the pupils of ground-based telescopes to improve the contrast achieved by a vortex coronagraph. This approach works well in the presence of a central obscuration and radial support structures. We analyze the contrast, off-axis throughput, and post-coronagraph point spread functions of an apodized vortex coronagraph designed for the European Extremely Large Telescope (E-ELT). This technique offers very good performance on apertures with large obscuring support structures similar to those on future 30-40m class ground-based telescopes.