Visualized Detection For The Surface Micro-defects Of Optical Elements

Total reflection prisms are the key elements in the laser gyroscope, the surface defects such as pits and scratches cause great damage to the prism and laser gyroscope. The detection for defects of optical element uses visual method for a long time, it is imperative to improve the detecting method because the visual method is inefficient and discrepant. This project can acquire bright image of defects in the dark background through laser beam oblique incidence on the element surface and scattering light imaging in the microscope system. The bright image is very easy to digitized and then the visualized high-precision detecting is realized.The test objects contain pits, scratches, flare outline. The research is mainly concentrated on the following aspects:1) In line with the requirement in the defects'examination, the scattering properties of micro-defects can be analyzed, and then images collecting about three working faces of the total reflection prism can be achieved by the microscopic imaging optical system which is putted up on the basis of the microscopic imaging method.2) It is indicated that the methods of median filtering and morphological filtering are better for filtering about the images of defects after comparatively analyzing four filtering methods; the threshold method is used to segmented images of flare outline and the method of edge extracting of Canny operator is used to segmented images of pits and scratches after comparatively analyzing the methods of the threshold and the edge extraction.3) The surface quality of optical elements can be divided into for levels though extracting gray level of flare outline and calculating the gray gradient.4) After a lot of analysis about geometrical characteristic data, circular degree and ratio of the minor axis and the major axis are used to sorted pits and scratches, and the eigenvalues are 0.055 and 0.550; the gray value of defects can be obtained, and the size of defects can also be measured using the number of pixels.The research is the trial and exploration on detecting surface defects of optical components using microscopic scattering imaging technique. It is useful for building of the detecting system of expert. The algorithm and method are valuable to engineering application proved by the testing.