Research On Optical Surface Defect Detection Based On Elastic Light Scatterin

In recent years,the rapid development of the demand for security lenses,vehicle lenses and smart phones has driven the structural adjustment of the optical components industry,and put forward higher requirements for the quality control of optical components,among which the surface quality of optical components has an important impact on the imaging quality of the whole system.At present,optical factories mainly use manual observation for surface defect detection,which is highly subjective and difficult to ensure consistency.Besides,it is difficult to inspect microscale scratches with high spatial resolution at a high efficiency based on machine vision technology.To solve this problem,this paper proposes to characterize scratches based on the elastic light scattering technology,and uses geometric optical approximation algorithm to numerically simulate the scattered light distribution of scratches under different lighting sources.An experimental measurement system is built,and multi-angle scattered light is used to retrieve the cross section shape of scratches,so as to realize high-resolution scratch measurement with large field of view and improve the measurement efficiency.Specific work is as follows:Firstly,a geometric optical approximation algorithm is proposed to calculate the scattered light distribution when a plane wave irradiates scratches of different sections,considering the diffraction effect.The effectiveness of the proposed algorithm is verified by comparing the simulation results with the exact electromagnetic solution,and it is applied to the scratch scattering problem of optical glass surface.Then,considering the effects of surface curvature and Gouy phase shift,a generalized geometric optics approximation algorithm with high computational efficiency is proposed to simulate the light scattering problem of large surface scratches of arbitrary cross-section shape.The effects of scratch parameters,refractive index,spectral bandwidth and other factors are systematically studied,which provides theoretical guidance for experimental measurement.Secondly,an optical surface scratch measurement system based on Angle resolution imaging was established.The scattered light distribution was obtained by changing the illumination Angle of the annular light source.The scratch parameters were inverted by converting the inverse scattering problem into an optimization problem based on geometric optics approximation algorithm and genetic algorithm.Experimental results show that the measurement system can effectively invert the 3D scratch profile.Based on the measurement of scattered light intensity,a lens with low magnification and large field of view can be used to measure the surface.Compared with the traditional direct measurement of scratch width using a lens with high magnification,this system significantly improves the measurement efficiency.Finally,the far-field scattering expression is derived based on the spherical vector wave function and boundary conditions.The directed scattering under Kerker condition is explained in detail and the expression of Bessel beam is derived.The scattered emission spectra of nanoparticles in angular polarized Bessel beams are studied.Based on the angular spectrum theory,the scattering condition is generalized for any scattering angles except forward scattering and back scattering,and the numerical solution verifies that the scattering can only occur in x Oz and y Oz planes.The simulation results show that scattered emission spectra are highly sensitive to particle parameters and can be applied to the characterization of nanoparticles,which provides a theoretical basis for the subsequent development of nanoscale defects.