Optical design for 3D detection of surface defects on ultra-precision curved optical elements based on micro structured-light

With the growing demand for ultra-precision curved optical element applications, the requirements for element quality are becoming more stringent. Surface defect detection, as one of the key aspects of quality control of optical elements, is crucial to ensure the performance of optical systems. Among them, the micrometer-wide and tens of nanometers-deep weak defects on the surface of ultra-precision optical elements are one of the most difficult points to detect. The commonly used structured-light detection method needs to adjust each component individually, and all the indexes are difficult to be considered and utilized simultaneously. So this paper develops an optimized design for 3D detection of weak defects on curved surfaces based on micro structured-light detection (MSLD), which can achieve a balance of field of view (FOV), depth of field (DOF), and resolution. The system is capable of realizing a FOV of 2 mm × 2 mm while achieving a width resolution of 1 μm. The system has been further manufactured, mounted, and built, and key indexes such as FOV, DOF, and resolution have been measured for the system to verify the validity of the design. Further detection experiments of weak defects with different shapes on the surfaces of curved optical elements are carried out and the results are compared with those of a white light interferometer (WLI), demonstrating that the designed MSLD system can achieve micrometer width resolution and nanometer depth resolution.