A Study On Ultrafast Laser Processing For Transparent Brittle Materials

With the development of science and technology, there is an increasing processing demand for transparent brittle materials such as cover lens and optical elements. Ultrafast laser technique has incomparable advantages in this field. However, This technology has met several challenges and limitations associated with the difficulties to further improve the processing efficiency, a large taper formed in the process and the thermal ablation problems.In this dissertation, the role of femtosecond and picosecond laser in transparent brittle materials processing was studied according to the related experiments. By using picosecond, the relations between various parameters and the ablation results were analyzed, and the principle was discussed as well. It was indicated that the ablation efficiency was mainly influenced by pulse energy, overlap rate and the processing numbers, and the sputtering area of the etching debris was mainly decided by the repetition frequency. Under the same energy condition, with the overlap rate for 30%, processing numbers for 50, and the frequency for 400-500 k Hz, a reasonable result could be achieved according to the research.Based on the research of the relevant principles, three new processing programs, the photosensitive coating method, helix-hoop-cut method and water infiltration method were applied and analyzed in this thesis.According to the experiments and tests, by using the photosensitive coating method, the absorption rate of the laser would be increase in the first stage of the ablation and as a result, the cutting efficiency could be improved 30% whiling cutting the thin(<200um) strengthened glass.The helix-loop-cut method also showed its advantages in laser cutting processing especially on thick(>200um) transparent materials. By means of adjusting the cutting route and energy distribution, this method was proved that it could reduce the waste of laser energy and promote the efficiency by about 43%, and in the meanwhile, it could increase the angle between ablation wall and the surface by about 4.5 degrees.Ensuring the incident energy density of the laser would not be greatly attenuated, the water infiltration method could significantly reduce the thermal damage of the surface of the material by using water cooling effect. And on the other hand, benefited by the spontaneously formed vortex action, the etching debris could effectively cleaned, which finally enhanced the interaction and resulted in the slightly reduced taper. What is more, by the co-use of helix-loop-cut method and water infiltration method, the wall of the cutting groove would finally reach almost vertical to the surface of the materials.By using the above three processing programs, the efficiency and quality of laser ablation could be significantly improved to some extent.