样品不应当过分大，以致不恰当地增加了衍射束的宽度。
The sample should not be so large as to increase unduly the width of the diffracted beam.
前言： 对用电子显微镜测量薄膜厚度的三种方法：双束衍射法、污斑法、污线法进行了实验及比较分析。
The experiments , comparison and analysis for the three thickness measurement methods :two-beam diffraction method , contamination spot method and contamination line method were carried out.
理论分析表明，通过对入射角进行优化可以得到衍射效率高且光强分布均匀的分束器。
Theoretical analysis shows that the splitter with high diffraction efficiency and uniform distributed light intensity can be designed by incidence Angle optimization.
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