【作者】 刘超；

【导师】 宣丽；

【作者基本信息】 中国科学院研究生院（长春光学精密机械与物理研究所） ， 光学， 2012， 博士

【摘要】 液晶自适应光学技术作为一种自适应光学新技术越来越受到人们的重视。一方面，液晶波前校正器拥有数百万的驱动单元，可以对畸变波前实现高精度的校正；另一方面，液晶波前校正器使用了二元光学衍射的原理产生光学波前，因此只要产生一个波长的调制量，便可实现数十个波长的校正深度。加之采用开环控制方式，液晶波前校正器所固有的偏振依赖问题可以得到有效解决。因此，开环液晶自适应光学系统非常有潜力应用于大口径望远镜。液晶自适应光学系统虽然优势巨大，但是缺点同样非常突出，目前最主要的一个问题是校正速度慢，带宽只有十几赫兹。带宽低的问题严重制约着液晶自适应光学技术在大口径望远镜上的应用。针对校正频率较低的问题，对波前探测器进行了优化设计，使得哈特曼波前探测器在保证探测精度的情况下探测频率从500Hz提高到909Hz，相当于系统的带宽从13Hz提高到19Hz。更进一步，通过采用并行的时序控制和优化的校正比例因子，又使系统的带宽从19Hz提高到23Hz。通过对湍流波面运动趋势的研究，发现湍流波面在9ms（湍流频率55Hz）内具有很强的相关性，因此提出湍流波前的相关模式预测。利用预测程序得到的校正效果可以比没有预测的提高10%。通过利用预测残差，对相关模式预测算法进行改进，使得预测系数可以跟随湍流频率的变化而自适应的发生改变，由此校正效果可比没有预测的进一步提高到23%，使带宽从22Hz提高到30Hz。最后，利用湍流波面的空间相关性构建了自适应斜率预测算法。经过其预测以后，校正效果可比直接校正提高26%，相当于带宽从直接校正的25Hz提高到36Hz。利用这套具有湍流预测功能的开环液晶自适应光学系统对天体目标进行了现场自适应校正，所得图像的分辨率达到1.8倍的衍射极限，获得了良好的成像效果。以上所开展的研究工作是对液晶自适应光学系统实用化有益的探索研究，将对液晶自适应系统在天文学上的应用起到一定的推动作用。更多还原

【Abstract】 Liquid Crystal Adaptive Optics have drawn more and more attention fromscientists and engineers as a new adaptive optics technology. On one hand, liquidcrystal wavefront corrector can achieve high wavefront distortion correction accuracywith millions of driving units. On the other hand, liquid crystal wavefront correctorcan gain a correction range of tens of wavelengths with a modulation depth of onlyone wavelength, by means of generating wavefront with binary optics diffraction. Theresponsing speed can be improved significantly as the modulation depth reduced.Moreover, with open-loop control mode, the intrinsic polarization dependenceproblem can be solved effectively. Hence, open-loop liquid crystal adaptive opticssystems (LCAOS) has a great potential to be applied to large aperture telescopes.Currently, the main problem of the open-loop LCAOS is that the correctionspeed is not enough, which limits the application of the LCAOS on large telescopes.For the problem of low correction frequency, the detecting frequency ofHartmann wavefront sensor is improved. With these renovations, the detectingfrequency increases from500Hz to909Hz. The system bandwidth is accordinglyincreased from13Hz to19Hz. By utilizing of a parallel sequential control and anoptimized proportional correction factor, the system bandwidth is further increasedfrom19Hz to23Hz. Through the research of the evolution of the atmospheric turbulence, we foundthat the correlation between adjacent turbulence wavefront within9ms (turbulencefrequency is55Hz) is strong. Based on this, a correlative modal predictive (CMP)algorithm is developed to further solve the problem of large time delay. Using theCMP to predict the real55Hz atmospheric turbulence, the result shows animprovement of10%compared to direct correction.By improving the CMP so that the predictive coefficients can adaptively fit to theturbulence, an adaptive modal predictive (AMP) algorithm is developed. Thecorrection result showed that it could improve23%compared to the direct correctionor the bandwidth is increased from22Hz to30Hz. Finally, the spatial correlation isintroduced to the AMP. It shows that the correction result could improve26%compared to the direct correction, or the bandwidth is increased from25Hz to36Hz.The resolution of the system reaches1.8times of the diffraction limit. Fine imagingresults were acquired in field adaptive correction of celestial objects.The work is a tentative research on the practicability of open-loop liquid crystaladaptive optics systems, and will have a significant influence on the astronomicalapplication of liquid crystal adaptive optics.更多还原