Research on Inversion Technology of Surface Defect Depth of Ultra-Smooth Optical Surfaces

For identifying the surface features of ultra-smooth optical or non-optical surfaces, light scattering analysis and measurement is a very useful method. Aiming at the requirement of detecting depth information of surface defects on ultra-smooth surfaces, the author propose a method of measuring the depth information about the surface defects of optical elements by using a relationship model between surface roughness and surface defects. The relationship between surface roughness and surface scratches is analyzed, and the relationship model is established. Then, by simulating the surface roughness with scratches and without scratches, according to the relationship model, the depth information of the surface of the optical component is calculated and the correctness of the model is verified. Finally, the length and width information of the surface scratches are measured according to the microscopic scattering dark field imaging method, the surface roughness is measured by white light interferometry, and the depth information of the surface scratches is calculated according to the above relationship model. The results are compared with the conclusion of the white light interferometer. The depth calculated by the roughness is basically consistent with the measured scratch depth, and the error is between 0.205 nm and 4.246 nm. Therefore, the experimental results demonstrate the effectiveness and feasibility of this proposed method.