Case Study 3: Adaptive Optics Systems

Abstract

Adaptive optics (AO) is an effective optical technique that enables ground-based astronomical telescopes to attain distinct images by reducing the effect of atmospheric turbulence on wavefronts of light waves. In this chapter, an AO system for a ground-based astronomical telescope is taken as an example to facilitate understanding of an optical system from its design to its implementation using both geometrical and wave optics. The image quality of a ground-based astronomical telescope is greatly degraded due to distorted wavefronts caused by the atmospheric turbulence of incoming light waves. To improve the image quality of the astronomical telescope, the distorted wavefronts of incoming light waves need to be compensated in real time, which is the work of AO. Although the basic idea of AO is simple, it is very difficult to implement a practical AO system because implementation involves multiple scientific branches and technical realms such as optics, automatic control, and electronics, among others. In order to provide a deep understanding of one AO system, this final chapter is structured as follows. First, the principles of AO are presented. Second, brief descriptions of an astronomical telescope and atmospheric seeing are given as prerequisites to designing a practical AO system. Third, the detailed design of an AO system for a telescope is illustrated. Then, the core components and related algorithms of the telescope AO system are given. Next, two criteria—one for the order estimation in the modal wavefront reconstruction, and the other for the matching problem between the Shark–Hartmann sensor and the deformable mirror—are discussed. Finally, the implementation and performance of the AO system are presented.