Coronagraph-Integrated Wavefront Sensing with a Sparse Aperture Mask

TL;DR

This paper introduces a novel method integrating a sparse aperture mask with a coronagraph to accurately measure low-order wavefront aberrations, enhancing exoplanet imaging by improving starlight suppression.

Contribution

The paper demonstrates how a sparse aperture mask can be integrated with a coronagraph to effectively sense and estimate low-order aberrations using fringe pattern analysis.

Findings

Accurately estimates Zernike phase modes up to n=5.

Compatible with Lyot and shaped pupil coronagraphs without degrading science beam.

Effective under low flux and short exposure conditions.

Abstract

Stellar coronagraph performance is highly sensitive to optical aberrations. In order to effectively suppress starlight for exoplanet imaging applications, low-order wavefront aberrations entering a coronagraph such as tip-tilt, defocus and coma must be determined and compensated. Previous authors have established the utility of pupil-plane masks (both non-redundant/sparse-aperture and generally asymmetric aperture masks) for wavefront sensing. Here we show how a sparse aperture mask (SAM) can be integrated with a coronagraph to measure low-order, differential phase aberrations. Starlight rejected by the coronagraph's focal plane stop is collimated to a relay pupil, where the mask forms an interference fringe pattern on a subsequent detector. Our numerical Fourier propagation models show that the information encoded in the fringe intensity distortions is sufficient to accurately discriminate and estimate Zernike phase modes extending from tip-tilt up to radial degree $n=5$, with amplitude up to $\lambda/20$ RMS. The SAM sensor can be integrated with both Lyot and shaped pupil coronagraphs (SPC) at no detriment to the science beam quality. We characterize the reconstruction accuracy and the performance under low flux/short exposure time conditions, and place it in context of other coronagraph wavefront sensing schemes.