Study On Propagation Properties Of Light Bean In Medium With Subsurface Damage

The subsurface damage of optical element has great influence on the performance of optical system. Laser Confocal Scanning Microscopy Technology(LCSMT) based on light scattering is one kind of subsurface nondestructive detection techniques with higher speed and resolution. The information of subsurface damage can be obtained and evaluated by scattering modulation signal of incident light. So the study on propagation properties of light in medium with subsurface damage is necessary for the comprehensive establishment of theoretical system of LCSMT.The common types and generation mechanisms of subsurface damage, the basic principle of LCSMT and the basic principle of Finite Element Method(FEM) are introduced; The FEM is applied to the study of subsurface damage in order to explore the scattering characteristics of subsurface damage, and the influence of different factors on scattering light signal is studied by simulation experiment when the focused light beam incident to the subsurface defects; The detection process of LCSMT is simulated and the variation of scattering light signal is analyzed in detection process; Laser confocal scanning microscopy system is built and scattering light signal from optical element’s subsurface area is collected. The change law of scattering light signal is compared with simulation result.The numerical models of particle detects and three kinds of micro-cracks (Lateral Crack, Hertz Conical Crack and Tail Indent Crack) detects in subsurface are established. The optical field distribution is simulated when glass medium with particles and these kinds of micro-cracks by using electromagnetic simulation software based on finite element method.On this basis, the detection process of LCSMT for subsurface area is simulated. The variations of light field distribution and scattering light intensity that are caused by subsurface particles and micro-cracks are studied in detection process.Laser confocal scanning microscopy system is built and the subsurface area of sample is measured. The experiment results verify the correctness of simulation experiment and effectiveness of numerical model, and show that the results of previous research on the variations of scattering light propagation properties caused by subsurface damage are correct. These results lay the foundation for the research on the subsurface damage detection theory.