Prediction Control And Multi-conjugate Technologies For Adaptive Optics System

The adaptive optics (AO) systems are time-delay servo systems and their performances are limited by the time lag in the systems. The traditional control algorithms used in AO systems do not have good performances and high control bandwidths since these algorithms have fixed control parameters and are not themselves adaptive. The technology of multi-conjugate adaptive optics (MCAO) can overcome the limitation of anisoplanatism and compensate the atmospheric turbulence over a very large field of view. The Large Binocular Telescope (LBT) in USA uses this technology. The secondary mirrors in LBT may have mechanical displacement in a way that would make the plate scale of the two MCAO systems change and cause trouble for LBT. The key to success of star-oriented MCAO is how to reconstruct the3D map of turbulence above the telescope and how to determine the tip and tilt over the observation object. Non-common path aberrations between the science camera and the wave-front sensor (WFS) in AO system are unseen by the WFS and therefore are not corrected in closed loop that will affect the performance of the system.The dissertation concentrates on prediction control algorithms and multi-conjugate technologies for AO system. The main contents and results are concluded as follows.Firstly, a linear prediction control algorithm used to predict the voltages of deformable mirror of AO system in advance has been studied. Numerical simulations are carried out to show the significant improvements brought by this algorithm.Secondly, a multichannel adaptive prediction control algorithm which can be applied to practical real-time closed-loop AO system has been investigated. Analyses on convergence, control performance and bandwidth of this algorithm have been made. Compared with the classical proportional-integral control and traditional prediction algorithm, simulation results show that the new algorithm can improve control properties and the closed-loop bandwidth of the system efficiently.Thirdly, the simulation of layer-oriented MCAO system has been implemented successfully.Fourthly, a method used to measure the plate scale change of LBT by use of the unoverlapping wave-front from the middle high WFS is proposed and relative simulations have been made to show the validity and the potential ability of this method.Fifthly, an algorithm used to reconstruct the3D map of turbulence for star-oriented MCAO is derived. The validity of this algorithm has been by demonstrated by simulations in which two and three layer phase screens are respectively reconstructed successfully.Sixthly, an algorithm to measure the tip and tilt over the observation object is proposed and has been validated by the relative simulations. The accuracy of this algorithm in terms of guide stars’magnitude, separation distance and the number of Zernike modes has been analyzed.Finally, a modified phase diversity technique used to measure the internal non-common path optical static aberrations is proposed and the relative simulations and experiments have been made to show the validity and the potential ability of this technique. The study shows that the method is very flexible and has the same accuracy as the traditional phase diversity.The prediction control algorithms for closed-loop adaptive optics systems proved by theory and simulations are meaningful on improving the performances and control bandwidths. The theory analysis and simulated results for multi-conjugate adaptive optics provide significant guidelines and help for developing MCAO system in the future. In general, for future high performance AO systems, the work in the dissertation may be of interest to achieve the challenging science goals.