Study On Illumination Characteristics Of Optical Surface Defects

As one of the three major influencing factors of surface quality,surface defect is a very important index to evaluate the quality of optical elements.Due to the existence of surface defects,not only will the optical surface produce diffraction fringes,scattering flares,lead to the destruction of the surface facial mask layer and the accumulation of beam energy,but also affect the imaging quality and service life of the components in the optical system.When detecting surface defects,by comparing the earliest manual visual method and other instrument detection methods,it can be found that the optical surface defect detection system based on micro dark field technology has higher sensitivity and more intuitive results,and can also meet the detection efficiency and accuracy.Therefore,since the discovery of this method,the micro dark field imaging method has gradually become the best application scheme in the field of surface defect detection.However,at present,the defect scattering theory for micro dark field imaging method is not complete,and the illumination characteristics are not clear and accurate.At present,the analysis is mainly based on experience or geometric optics theory in system structure selection and parameter setting,which does not meet the high-precision detection requirements of smaller and weaker surface defects,and can not effectively guide the acquisition of high-quality images.In order to meet the detection requirements of optical surface defects,firstly,the scattering theoretical model for surface defects is established,and the effects of lighting source and defect geometric characteristics on defect scattering imaging are simulated and analyzed.Then,based on the micro dark field imaging method,the optical surface defect detection system is designed and built,and the verification experiment is carried out.This paper mainly includes the following research contents:Firstly,the research status of optical surface defect detection technology and the commonly used detection methods are discussed,with emphasis on the detection principle based on optical scattering method.According to the detection principle of micro dark field method,its system composition and the influence of various influencing factors on the intensity and distribution of scattered field are analyzed.Secondly,the calculation and characterization method of scattering field intensity is analyzed.Based on vector scattering theory and bidirectional reflection distribution function,the scattering theoretical model of optical surface defects is established,and then the software simulation calculation of this model is carried out.The effects of geometric characteristics such as defect depth,defect width,incident angle of light source,incident light direction,incident light wavelength and light polarization on the light field distribution and scattered field intensity of surface defects are analyzed.According to the simulation results,the optimal lighting conditions are proposed.Finally,by adding the detection technology based on multispectral and polarization to the defect detection system of micro dark field imaging,the optical surface defects are detected.The experiment of analyzing the scattering characteristics of defects is carried out,and the experimental results are compared with the distribution law of scattering field obtained by simulation,so as to clearly select the best lighting source conditions for high-quality optical surface defect images.At the same time,the analysis of the experimental results shows that the detection accuracy of the micro dark field imaging system can be improved when using multispectral technology and polarization technology to detect optical surface defects.