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本文阐述了离轴照明提高曝光分辨率和增加焦深的原理，应用Ｈｏｐｋｉｎｓ理论研究了其成像特性。给出了两种离轴照明方式──四极照明和环形照明下的空间像分布，并和传统照明方式下的空间像分布作比较。计算结果说明，采用离轴照明使得曝光分辨率和焦深得到了很大的提高。
This paper describes the principle of off-axis illumination to improve the exposure resolution and increase the depth of focus. The Hopkins theory is used to study its imaging characteristics. Two kinds of off-axis illumination methods are given - the spatial image distribution under quadrupole illumination and ring illumination, and compared with the spatial image distribution under the traditional illumination mode. Calculation results show that the use of off-axis illumination makes the exposure resolution and depth of focus has been greatly improved.