偏振对光学系统成像质量的影响

摘要

Normally, Strehl ratio, resolution, and focus depth, the parameters that are used to evaluate the performance of an optical imaging system, are always calculated by scalar diffraction method. Considering the vectorial properties of light, especially when the system numerical aperture (NA) is high, the accuracy of scalar method can no longer fulfill the requirement of analysis. The variations of properties of these parameters accompanied by using of vectorial method are discussed. In order to describe the effects of polarization clearly, assuming a system with identical polarization state within the entrance pupil, by formula deduction and numerical simulation, we conclude that due to the influence of the polarization, the maximum intensity of system diffraction spot decreases, the resolution between image plane and parallel polarized orientation of incident light drops down, then the diffraction spot loses its circular symmetry, the focus depth changes slightly, and these effects becomes more apparent with the increase of system NA. Finally, the method of calculating the off-axis images is discussed in the paper.%通常情况下，评价光学成像系统像质的几个重要参数，如能量集中度（StrehlLk）、分辨率、焦深等，都是以标量衍射理论为基础进行计算和分析的．考虑光波的矢量偏振特性，尤其是在高数值孔径系统中，标量衍射的精度已不能满足精度要求．本文讨论了在采用矢量衍射计算方法基础上，上述成像参数的变化，所讨论系统入瞳面各点为偏振方向一致的线偏光或部分偏光，以便于考察偏振对所述成像参数的影响，通过公式推导和数值计算，得出了由于偏振的影响．系统衍射斑能量极大值变小，像面和偏振平行方向分辨率降低，分辨率出现各向异性，只有系统焦深受偏振影响较小．而这些矢量效应会随着系统数值孔径的提高而愈加明显，因此在分析处理数值孔径较高的光学系统时必须使用矢量衍射方法．最后讨论了轴外点衍射斑的计算．