Study On Optical Sub-Surface Damage Evaluation Technology

Sub-surface damage (SSD) in optical elements had became a shackle of research and manufacture in energy, military, advanced technology and so on, for its severe influence to the laser-induced damage threshold (LIDT), the image quality and thin film, the long term stability of large optical system. So the evaluation of SSD was a hot topic in optical engineering. Laser scanning confocal technology (LSCT) was used widely in biology, medicine and materials science. It was introduced in the paper to test SSD. The research works as follow:1 Based on the analysis of SSD cause and type, Mie scattering theory was applied in LSCT; SSD scattering principle in confocal illumination was analyzed; the computing formula was given, which was about one point's scattering power in SSD detected by LSCT sensor; formula's simulation was showed from microobjective numerical aperture (NA), optical source wave-length, relatively refraction index.2 Optical power meter was chosen as the photoelectric sensor and signal transmission; 15mw/405nm laser was selected as the optical source; through great amount of experiments, 5μm pinhole was confirmed as the confocal filter; control software suiting for the scan bench was compiled. Then the 2D scanning laser micro system was founded.3 Three optical surface samples, which were fabricated through different process, were tested. Undesired signal was analyzed and the signal coming from sample SSD scattering was obtained effectively; the samples were measured by the 2D scanning system, and their SSD distribution was give in contour maps.The consistency between experiment and theoretical analysis proved the feasibility of test method.