夫琅和费衍射与大角度衍射

众所周知,夫琅和费衍射的解析强度分布和暗纹位置是在一系列近似情况下导出的。其中最重要的条件是观测点必须限制在傍轴附近,衍射角不能太大,否则得不到简单的解析公式,也就不能称之为夫琅和费衍射。最近发现有人发明错误的理论将夫琅和费衍射概念及其测量扩展到90°角,其结论与常识截然相反,因此,有必要把混淆的概念予以澄清。

Fraunhofer diffraction and large-angle diffraction

It is well-known that the analytical intensity expression and the locations of the dark fringes of Fraunhofer diffraction are obtained under a series of approximations.The most important approximation for Fraunhofer diffraction is that the observation point must be limited close to the axis,or the diffraction angle is not too large.Otherwise no analytical expression can be obtained and thus cannot be called Fraunhofer diffraction.Recently it is found that a wrong theory was developed which has extended the diffraction angle to up to 90°.This is obviously contra-intuitive and misleading.This paper is to clarify the confused concepts about Fraunhofer diffraction and its applications to measure objects with small geometrical sizes.