SIPM Makes Progress in Femtosecond Laser Modification Of Silicon Carbide Surface To Enhance Polishing Efficiency Research

Recently, Wei Chaoyang's team at the Precision Optical Manufacturing and Testing Center Laboratory of the Shanghai Institute of Optical Precision Machinery, Chinese Academy of Sciences, has made progress in the study of femtosecond laser modification of silicon carbide surfaces to improve polishing efficiency. It is found that the surface modification of RB-SiC pre-coated with Si powder by femtosecond laser can obtain a surface modification layer with a bonding strength of 55.46 N. The surface modification layer can also be modified by femtosecond laser to improve the polishing efficiency. The modified RB-SiC surface can be polished for only 4.5 hours to obtain an optical surface with a surface roughness Sq of 4.45 nm, which is more than three times more efficient than direct polishing. The results extend the surface modification method of RB-SiC, and the controllability of the laser and the simplicity of the method make it possible to be used for the surface modification of RB-SiC with complex contours. The related results were published in Applied Surface Science.

RB-SiC, as a silicon carbide ceramic with excellent properties, has become one of the most excellent and feasible materials for lightweight and large telescope optical components, especially for large-size and complex-shaped mirrors. However, RB-SiC, as a typical high-hardness, complex-phase material, has 15%-30% residual silicon remaining in the blank when liquid Si reacts chemically with C during the sintering process. And the difference in the polishing properties of these two materials will form micro-steps at the junction of SiC phase and Si phase components during the surface precision polishing process, which is prone to diffraction, and is not conducive to obtaining high-quality polished surfaces, and poses a great challenge to the subsequent polishing.

To address the above problems, the study proposes a femtosecond laser surface modification pretreatment method, which utilizes a femtosecond laser to modify the RB-SiC surface pre-coated with silicon powder, which not only solves the problem of surface scattering due to the difference in the polishing performance of the two phases, but also effectively reduces the difficulty of polishing and improves the efficiency of polishing of the RB-SiC substrate. The results show that the pre-coated Si powder on the RB-SiC surface is oxidized under the action of femtosecond laser, and with the oxidation gradually penetrating deeper into the interface, the modified layer forms a bond with the RB-SiC substrate. By optimizing the laser scanning parameters to adjust the oxidation depth, a high-quality modified layer with a bond strength of 55.46 N was obtained. The modified layer is easier to polish compared to the RB-SiC substrate, allowing the surface roughness of the pretreated RB-SiC to be reduced to Sq 4.5 nm in just a few hours of polishing, which is more than three times more efficient compared to the abrasive polishing of the RB-SiC substrate. In addition, the method's simple operation and low requirements on the surface profile of the RB-SiC substrate can be applied to more complex RB-SiC surfaces and significantly improve the polishing efficiency.