Crystal Micro Defect Detection Based on Four Focal Length Phase-Coherent Machine Vision
Focusing on the problem of low detection accuracy in the minor internal defect detection of crystals,a method based on four focal length phase-coherent machine vision is proposed.The phase information of crystal internal defects is turned into gray level through four focal length phase-coherent optical path.Then a feature image of crystal internal defects is formed.The missing points in the feature image can be extracted by using machine vision algorithm.After feature extraction and gray analysis of the feature image,the thickness of crystal internal defects is obtained.The simulated defect of 60 nm silica film coated on the center of plexiglass surface is tested,the results show that the relative error of the method is 1.83％and the detection resolution reaches the order of nanometers.Com-pared with the relative error of 2.4％of the dynamic Teman interferometer and the 40 μm detection resolution of laser focusing line scanning method,it has good improvements.The results also prove that the method proposed can be effectively applied to the detection of minor defects in the crystal.
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