大口径拼接镜面望远镜衍射极限成像新技术研究

All large aperture telescopes such as Keck and future TMT employ the segmented-mirror technique. The static phase error from the segments, especially the piston wave-front error, is one of the most significant errors to reach diffraction-limited imaging. In this proposal, we will research on the critical technique on the diffraction-limited imaging of large aperture segmented-mirror telescopes. Here we firstly propose in the world to employ one segmented surface deformable mirrors (DM) and the iterative optimization controlling algorithms for the correction of static wave-front errors of the segmented-mirror telescopes. A fore-optics will be induced to re-image each segmented mirrors of the telescope on the segmented DM. The target goal of this proposed project is to initially demonstrate the feasibility of such technique to correct the static phase error in large aperture segmented-mirror telescopes by laboratory experiment research. In the first step, the static point spread function (PSF) of the telescope will be reconstructed, which include only the phase error from the segments; then we will introduce our previously developed iterative optimization technique to control the segmented DM to reconstruct the static PSF, in which the static phase error can be precisely measured. Finally, the static phase error can be corrected by applying the opposite phase by the DM. Such a technique will be promising to be used for the diffraction-limited imaging of current segmented-mirror telescopes and will provide a solid foundation for the extreme high-contrast imaging based on future extremely large telescopes.

现有Keck和未来TMT等望远镜均采用拼接镜面技术，来自望远镜自身的静态相差(尤其是piston相差)是制约衍射极限成像的主要因素。项目针将对大口径拼接镜面望远镜衍射限成像的关键技术开展研究，提出基于分立表面可变形镜（DM）和多次迭代数值优化控制算法的静态波相差校正新技术，通过中继光学将望远镜拼接子镜一对一成像到DM之上，而后对其相差进行精确校正。项目将主要通过实验来验证该技术的可行性，以初步解决大口径拼接镜面望远镜静态相差的精确校正问题。实验系统将首先重构该望远镜的静态点扩散函数（PSF），该PSF仅包括拼接镜引入的波相差信息；进而采用前期发展的数值优化技术来控制DM，通过精确重构望远镜的PSF来测量其静态波相差；最后闭环控制DM施加反向波面来校正该波相差。此方法将有望解决现有拼接镜面望远镜的衍射极限成像问题，并为基于未来极大口径望远镜开展“超高”对比度成像研究做好技术储备。

现有Keck和未来TMT等望远镜均采用拼接镜面技术，来自望远镜自身的静态相差(尤其是piston相差)是制约衍射极限成像的主要因素。项目针将对大口径拼接镜面望远镜衍射限成像的关键技术开展研究，提出基于分立表面可变形镜（DM）和多次迭代数值优化控制算法的静态波相差校正新技术，通过中继光学将望远镜拼接子镜一对一成像到DM之上，而后对其相差进行精确校正。本项目研制子镜拼接望远镜静态PSF模拟和重构子系统，从理论上解决了拼接镜面结构望远镜Piston波相差重构和校正问题，完成了拼接镜面望远镜入射光瞳结构的系统模拟，成功重构了分布于每个子镜的Piston波相差，相差重构精度优于1/1000。该技术能够实际应用的关键在于要了解望远镜自身的静态PSF（带有波像差）。对此，项目组通过采集天文实测数据，验证了重构望远镜静态点扩散函数（PSF）算法；随后，结合我国近期提出的12米望大型光学/红外望远镜（LOT）主镜光学系统设计方案，根据项目提出的衍射极限成像方案研究了LOT望远镜入射光瞳结构；本项目通过两块可变形镜，前置DM用于模拟望远镜的拼接镜面结构及静态PSF成像，并通过引入气流扰动验证其静态PSF构造的实验性能，另外一套DM将用于产生和拼接子镜一一对应的相位，以精确探测和校正系统的静态相差，系统能够有效校正Piston波相差，获得衍射极限成像。本项目有效的解决了拼接镜面望远镜衍射极限成像问题，为未来极大口径望远镜的建设和基于该类望远镜开展系外行星高对比度成像研究奠定重要的技术基础。