利用菲涅尔衍射测量微小尺寸

Measurement for micro size by Fresnel diffraction

在科研工程实际中,对细丝、狭缝等微小尺寸的测量通常采用夫琅和费衍射法,因为衍射暗斑间距与被测尺寸之间具有很简单的函数关系:s=λL/d。理论上,夫琅和费衍射条件是相当苛刻的,即要求L>d^2/λ,在实际应用中,考虑到光源、传感器以及被测对象尺寸之间的匹配关系,往往很难实现。本文通过理论分析与实验数据充分证明,对于菲涅尔衍射,前述函数关系也能保持极为良好的近似,为仪器结构设计提供了极大方便,同时也为提高测量精度,扩展测量范围创造了有利条件。

In the research and engineering applications, the measurement for width of narrow slit or diameter of filament was generally based on Fraunhofer diffraction because there is asimple function between the size to be measured and space of diffraction minima: s - λL/d. In practice, the Fraunhofer diffraction are quite strict, i.e. L > d2/λ ,so the condition is difficult to satisfy due to the size of sensor might fault to match with the object to be measuredλ for any given size. By analyses and experiments it has been proven that the simple function mentioned above can be extended to Fresnel diffraction field with good precise. This result is very valuable since the structure of instrument can be very simple with high accuracy and wide measurement range.