Towards understanding interactions between the AO system and segment co-phasing with the vector-Zernike wavefront sensor on Keck

TL;DR

This paper demonstrates on-sky segment co-phasing control on Keck using a vector-Zernike wavefront sensor, improving image quality and exploring interactions between adaptive optics and segment alignment methods.

Contribution

It extends previous work by implementing a vZWFS for real-time segment co-phasing and compares different alignment strategies for enhanced telescope performance.

Findings

vZWFS improves Strehl ratio by up to 10% on Keck.

Successful on-sky closed-loop segment co-phasing achieved.

Insights into AO system interactions with segment phasing methods.

Abstract

We extend our previous demonstration of the first on-sky primary mirror segment closed-loop control on Keck using a vector-Zernike wavefront sensor (vZWFS), which improved the Strehl ratio on the NIRC2 science camera by up to 10 percentage points. Segment co-phasing errors contribute to Keck contrast limits and will be necessary to correct for the segmented Extremely Large Telescopes and future space missions. The goal of the post-AO vZWFS on Keck is to monitor and correct segment co-phasing errors in parallel with science observations. The ZWFS is ideal for measuring phase discontinuities and is one of the most sensitive WFSs, but has limited dynamic range. The Keck vZWFS consists of a metasurface mask imposing two different phase shifts to orthogonal polarizations, split into two pupil images, extending its dynamic range. We report on the vZWFS closed-loop co-phasing performance and early work towards understanding the interactions between the AO system and segment phasing. We discuss a comparison of the AO performance when co-phasing by aligning segment edges, as is currently done at Keck, compared with aligning to the average phase over the segments, as is done by the vZWFS.