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To overcome the hysteresis of a tip/tilt mirror(TTM)in an adaptive optical system and to improve its linearity and control precision,this paper researches the nonlinear effects of the TTM.A compensation method based on the frequency-dependent Mutified-Prandtl-Ishlinskii(MPI)model is proposed for online adaptive inverse compensation of the hysteresis nonlinearity of the TTM.By combining with PID feedback control algorithm,an adaptive inverse feedforward composite control algorithm is proposed.In which,the adaptive inverse feedforward overcomes the hysteresis curve changes due to the frequency factors,and the PID algorithm improves the overall control performance.A second-order model of the TTM is established to estimate the output of the TTM system,which solves the reference signals of the MPI model,avoids adding extra feedforward sensors,and ensures the utilization of light energies.Experiment results indicate that this algorithm effectively solves the problemof hysteresis nonlinearity of the TTM,the 15 Hz hysteresis ratio of the TTM fells from 24.28% to1.17%,and the linearity is improved by about 95%.As compared with the traditional PID algorithm,the control precision has increased by about 60%.It concludes that this composite control algorithm can compensate the hysteresis nonlinearity of the TTM effectively,and the control precision of the TTM is improved in adaptive optical systems.

To decrease the influence of defocus on liquid crystal adaptive optics system,improve the imaging quality,a mechanism for defocus compensate has been designed.The mechanism was based on liquid lens,which can change the focal length continuously without any moving part.In order to design the adjust mechanism reasonably,calculation have been taken on the relationship between the rotation angle of the outer ring and the deflection of film center.Then 0.2 diopter is choosen as the division value.The parameters of the mechanism were based on relationship between the rotation angle of the outer ring with deflection of film center and the division value.It shows a good performance in liquid crystal adaptive optics system.

When atmospheric turbulence coherence length r0 is measured by traditional Differential Image Motion Monitor(DIMM) method,it is difficult to obtain a stable r0 value due to limitation of light spot pairs.Therefore,this paper proposes a statistical method to increase the statistical number of light spot pairs from one on a wavefront to twelve aligned in a square,and completes the statistics on a SHWFS light spot array captured by the Shack-Hartmann wavefront detector.The method spatially increases the statistical number of samplings and the spatial symmetry of r0 measurement,so it decreases the statistical time greatly.The experiments show that only three hundred of wavefront samples gotten in 300 ms are enough to obtain the r0 with a variation less than 3%.The presented method solves the large error problem in the traditional r0 measurement for long time,and has contributed to the improvement of imaging accuracy of adaptive optical systems for ground-based telescopes

Advances in Liquid Crystal Adaptive Optical Systems(LC AOS) are described for Changchun Institute of Optics,Fine Mechanics and Physics,Chinese Academy of Sciences(CIOMP,CAS) in this paper.For two bottlenecks of low energy utilization ratio and slow correction frequency in LC AOS problems,a series of effective methods are presented by the LC AOS working group.The low energy utilization ratio has been improved from 5% to 85%,which is similar to that of the deformable mirror based AOSs.Furthermore,the correction frequency of the LC AOS is also greatly improved from 5 Hz to 140 Hz,which is closed to the ability of correction for atmospheric turbulence.According to these research results,two LC AOSs which correspond to a 2.16 meter Telescope(located at Xinglong Station of Beijing Astronomical Observatory) and a 1.2 meter telescope(located at CIOMP,CAS) are designed to correct the stars.Obtained results show that the resolution ability of the star for the 1.2 meter telescope is up to 3 times of the diffraction limitation.