Research On The Scattering Characteristics Of Sub-surface Damage Based On Tomography Method

Fracture, deformation, impurities and other internal defects generated in the near surface region in the machining process of the optical element is called the sub-surface damage(SSD).In recent years, the research of SSD detection technology of optical components is a hot issue in optical engineering. Due to the concealment of surface damage, there are many difficulties on its detection. Accordingly, Laser Scanning Confocal measurement techniques are proposed in recent years which are a non-destructive measuring method. It uses the sub-surface damage defects on the scattering of the incident light to evaluate the sub-surface damage of the optical element.This paper adopts the finite difference time domain method (FDTD) and with the help of the simulation software, the geometric model of the actual measurement on the basis of the reasonable assumptions is established. The light scattering properties of the laser confocal measurement techniques and its confocal detection signal intensity changes are studied. The way of using a light wave scattering theory to study the subsurface damage distribution characteristics of the optical components is proposed firstly in this paper. The advantage of this way is it can better understand the scattering characteristics of subsurface damage, and provide a theoretical guidance for the further research on the detection method. The main research content includes:1)The construction of subsurface damage scattering model of optical components is introduced. First the principle of the laser confocal chromatography measurement and the theory of the light scattering calculations is described. Then the finite-difference time-domain (FDTD) calculation method for this paper is determined and the laser confocal chromatography measurement model is established;2)The Simulation Experimental analysis is performed on the above calculation method and the geometric structure of the actual measurement.This part includes the detailed study of the simulation of the ideal state, the light scattering distribution of micro-cracks and bubbles, integral area description and simulation of common types of defects, such as micro-cracks and bubbles scattered distribution and detector comparative analysis of the received signal strength, analog simulation experiments under a variety of shape parameters and optical parameters, conclusions show that the simulation results are consistent with the theoretical analysis;3)The FDTD algorithm combined with simulation software are used to achieve a focused spot in different subsurface damage type of the optical components has a different scattered light field distribution. And then fitting the curve of the change in intensity of the light scattering signals during the tomography measurement process.The subsurface damage of optical components can be obtained by the simulation of the optical field distribution and intensity curve of the light scattering signals. At the same time compared the simulation result with the laser scanning confocal system experimental detection result about the subsurface damage in optical components,The experimental results show subsurface damage information change trend is consistent.Both the theoretical analysis and simulation studies have proved that the laser scanning co nfocal system is an effective method for the subsurface damage measurements of optical eleme nts. At the same time, the laser scanning confocal system provides a theoretical basis for the foil ow-up research and analysis of subsurface damage.