Laser Optical Characterization of Smooth Surfaces with Respect to Roughness and Defects in the Micrometer Range

Processes for the production of optically smooth surfaces are very costly. This is due to a long machining time (ultra-precision machining) or due to a large amount of material that is processed in a short time (rolling). In-process and in-situ surface quality monitoring is a basic precondition to reduce rejections and costs. Adequate quality parameters are the roughness and the number and kind of local defects per surface area. Optical measuring techniques (light scattering, interferometry) and digital image processing enable a fast surface characterization. The paper describes the modeling, simulation and application of a scattered light roughness measuring process based on the Kirchhoff theory and a microscopic imaging measuring process for local defect identification. Corresponding measuring results from stainless steel sheet substrates are presented.