Requirements for dynamic characteristics of adaptive optics systems

Dynamic characteristics of adaptive optics systems operating with radiation transmitted through a turbulent atmosphere are analysed on the basis of analytical calculations of the Strehl ratio using the theory of optical wave propagation in randomly inhomogeneous media and the model of an active mirror-corrector. A traditional adaptive optics system with a finite response time is described as a dynamic system with a constant delay. An expression is obtained that relates the most important parameters of the system, such as the error and frequency of the wavefront sensor, the aperture size of the optical system, and atmosphere parameters (the Fried parameter and wind velocity), with an attainable value of the Strehl ratio. It is confirmed that the admissible time delay in such a system is comparable with the time of transfer of turbulent inhomogeneities over a distance of the order of the coherence radius at an average wind velocity. Differences between open and closed loops in adaptive optics tracking systems are analysed. The possibility of using a 'predictive' algorithm for adaptive correction is demonstrated.