A Closed Loop Layer‐oriented Adaptive Optics Test Bed: Applications to Ground‐Layer Adaptive Optics

Abstract

Turbulence in Earth's atmosphere severely limits the achievable image quality of ground-based optical telescopes. With the technique of adaptive optics, the induced distortions of the light can be measured and corrected in real time, regaining nearly diffraction limited performance. Unfortunately, when using a single guide star to measure the distortions, the correction is only useful within a small angular area with a radius of ∼3″ centered on the guide star. This paper presents a laboratory setup, using four simulated natural guide stars and one deformable mirror to measure and correct turbulence-induced distortions over ∼35′ × 22″. With such a layer-oriented ground-layer adaptive optics (GLAO) system, the area of useful correction is significantly increased. We characterize a test bed for such a system in static and dynamic operation and verify the principles of the layer-oriented technique in closed loop operation. Furthermore, we study the influence of nonconjugated turbulent layers and the effect of brightness variations of the guide stars and derive results very similar to theoretical predictions and numerical simulations. © 2007. The Astronomical. Society of the Pacific. All rights reserved.