无遮拦离轴天文望远镜偏振像差分析及其对光学椭率的影响

随着天文探测水平的提高,偏振像差对天文望远镜成像质量的影响逐渐凸显。基于偏振光线追迹,分析了一种用于探测宇宙弱引力透镜效应的无遮拦离轴天文望远镜的偏振像差,得到了该望远镜的琼斯瞳、振幅响应矩阵以及望远镜中各个反射镜的二向衰减和相位延迟分布特性。计算发现偏振像差会影响该望远镜的成像对比度,同时还会改变其点扩展函数的空间分布。计算了偏振像差对望远镜光学椭率的影响,结果表明偏振像差会导致该望远镜光学椭率在全视场范围内发生不同程度的变化,最大改变量为7.5×10^-3,平均改变量为2.7×10^-3。在视场[-0.0487°,0.155°]附近,偏振像差使得该望远镜光学椭率最大插值误差由1.2×10^-4增大为1.1×10^-3。本文研究结果表明,对于探测弱引力透镜效应等要求超高成像质量的天文望远镜,偏振像差不可忽略,需要进行优化设计。

Polarization Aberrations in an Unobscured Off-Axis Astronomical Telescope and Their Effects on Optics Ellipticity

Because of the continuously increasing detection ability in astronomy,polarization aberrations are playing increasingly important roles in the performance of astronomical telescopes.In this paper,the polarization aberrations of an unobscured off-axis astronomical telescope used to detect weak gravitational lensing effect are analyzed using polarization ray tracing.The diattenuation map and retardance map of each mirror for the telescope are obtained,and both its Jones pupil and amplitude response matrix are determined.It is found that the polarization aberrations of the telescope have an impact on both the imaging contrast and the spatial distribution of the point spread function(PSF).The optics ellipticity of the telescope is analyzed.The variations of optics ellipticity,which are dependent on the field of view(FOV),are induced by polarization aberrations.The maximum and mean variations of the optics ellipticity in all FOVs are 7.5×10^-3 and 2.7×10^-3,respectively.At the FOV[-0.0487°,0.155°],the maximum ellipticity interpolation error increases from 1.2×10^-4 to 1.1×10^-3.Our analyses reveal that polarization aberrations should not be ignored and should be optimized in telescopes that require ultrahigh imaging performance,such as those used for detecting weak gravitational lensing effect.