High Resolution Imaging in the Visible with Faint Reference Stars on Large Ground-Based Telescopes

TL;DR

This paper introduces a novel pupil-plane curvature wavefront sensor that enables high-resolution visible imaging on large ground-based telescopes using faint guide stars, significantly improving image quality and resolution.

Contribution

The paper presents a new curvature wavefront sensor design and wavefront fitting routines that allow routine high-resolution imaging with faint guide stars on large telescopes.

Findings

Angular resolution improved by a factor of 2.5 to 3.

Faint guide stars (I 17m) can be used for near diffraction-limited imaging.

Simulations match hardware performance, enabling routine high-quality imaging.

Abstract

Astronomers working with faint targets will benefit greatly from improved image quality on current and planned ground-based telescopes. At present, most adaptive optic systems are targeted at the highest resolution with bright guide stars. We demonstrate a significantly new approach to measuring low-order wavefront errors by using a pupil-plane curvature wavefront sensor design. By making low order wavefront corrections we can deliver significant improvements in image resolution in the visible on telescopes in the 2.5m to 8.2m range on good astronomical sites. As a minimum the angular resolution will be improved by a factor of 2.5 to 3 under any reasonable conditions and, with further correction and image selection, even sharper images may be obtained routinely. We re-examine many of the assumptions about what may be achieved with faint reference stars to achieve this performance. We show how our new design of curvature wavefront sensor combined with wavefront fitting routines based on radon transforms allow this performance to be achieved routinely. Simulations over a wide range of conditions match the performance already achieved in runs with earlier versions of the hardware described. Reference stars significantly fainter than I 17m may be used routinely to produce images with a near diffraction limited core and halo much smaller than that delivered by natural seeing.