Laser-only adaptive optics achieves significant image quality gains compared to seeing-limited observations over the entire sky

TL;DR

This study demonstrates that laser-only adaptive optics significantly improves image quality across the entire sky without the need for bright guide stars, expanding observational capabilities for faint-target astronomy.

Contribution

The paper introduces a laser-only adaptive optics method that achieves substantial image quality gains without tip-tilt correction, enabling full sky coverage.

Findings

39% average improvement in effective FWHM

50% encircled-energy performance comparable to diffraction-limited

Laser-only AO increases sky coverage for faint-target observations

Abstract

Adaptive optics laser guide star systems perform atmospheric correction of stellar wavefronts in two parts: stellar tip-tilt and high-spatial-order laser-correction. The requirement of a sufficiently bright guide star in the field-of-view to correct tip-tilt limits sky coverage. Here we show an improvement to effective seeing without the need for nearby bright stars, enabling full sky coverage by performing only laser-assisted wavefront correction. We used Robo-AO, the first robotic AO system, to comprehensively demonstrate this laser-only correction. We analyze observations from four years of efficient robotic operation covering 15,000 targets and 42,000 observations, each realizing different seeing conditions. Using an autoguider (or a post-processing software equivalent) and the laser to improve effective seeing independent of the brightness of a target, Robo-AO observations show a 39+/-19% improvement to effective FWHM, without any tip-tilt correction. We also demonstrate that 50% encircled-energy performance without tip-tilt correction remains comparable to diffraction-limited, standard Robo-AO performance. Faint-target science programs primarily limited by 50% encircled-energy (e.g. those employing integral field spectrographs placed behind the AO system) may see significant benefits to sky coverage from employing laser-only AO.