A tomographic algorithm to determine tip-tilt information from laser guide stars

TL;DR

This paper introduces a geometric method to extract partial tip-tilt information from laser guide stars in multi-LGS adaptive optics systems, enhancing high-altitude correction and potentially improving sky coverage.

Contribution

A novel geometric approach to determine up-link tip-tilt from LGSs and an adaptation of the Learn and Apply algorithm for improved tomographic AO.

Findings

Good high-altitude tip-tilt correction demonstrated

Method shows limited performance for low-altitude tip-tilt

Combining with off-axis NGSs could enhance sky coverage

Abstract

Laser Guide Stars (LGS) have greatly increased the sky-coverage of Adaptive Optics (AO) systems. Due to the up-link turbulence experienced by LGSs, a Natural Guide Star (NGS) is still required, preventing full sky-coverage. We present a method of obtaining partial tip-tilt information from LGSs alone in multi-LGS tomographic LGS AO systems. The method of LGS up-link tip-tilt determination is derived using a geometric approach, then an alteration to the Learn and Apply algorithm for tomographic AO is made to accommodate up-link tip-tilt. Simulation results are presented, verifying that the technique shows good performance in correcting high altitude tip-tilt, but not that from low altitudes. We suggest that the method is combined with multiple far off-axis tip-tilt NGSs to provide gains in performance and sky-coverage over current tomographic AO systems.