Generating Artificial Reference Images for Open Loop Correlation Wavefront Sensors

TL;DR

This paper introduces a software method to generate larger reference images for Shack-Hartmann wavefront sensors, significantly improving their ability to measure large shifts in open-loop adaptive optics systems without external data.

Contribution

The authors present a novel technique for synthesizing larger reference images that enhance the performance of correlation wavefront sensors in open-loop regimes.

Findings

Increases measurable shifts from 12% to 50% of sub-aperture field in solar AO.

Extends accurate centroid measurement from 12% to 25% in laser guide star AO.

Requires no external data, enabling easy software upgrades.

Abstract

Shack-Hartmann wavefront sensors for both solar and laser guide star adaptive optics (with elongated spots) need to observe extended objects. Correlation techniques have been successfully employed to measure the wavefront gradient in solar adaptive optics systems and have been proposed for laser guide star systems. In this paper we describe a method for synthesising reference images for correlation Shack-Hartmann wavefront sensors with a larger field of view than individual sub-apertures. We then show how these supersized reference images can increase the performance of correlation wavefront sensors in regimes where large relative shifts are induced between sub-apertures, such as those observed in open-loop wavefront sensors. The technique we describe requires no external knowledge outside of the wavefront-sensor images, making it available as an entirely "software" upgrade to an existing adaptive optics system. For solar adaptive optics we show the supersized reference images extend the magnitude of shifts which can be accurately measured from 12% to 50% of the field of view of a sub-aperture and in laser guide star wavefront sensors the magnitude of centroids that can be accurately measured is increased from 12% to 25% of the total field of view of the sub-aperture.