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Fused silica optics, as key components in high - power laser systems, are prone to produce laser damage with different sizes under laser irradiation. For large - size laser damage, CO2 laser can be used for repairing process. For small - size laser damage, magnetorheological finishing (MRF) technique is appropriate. This work focused on the MRF repairing process of small - size laser damage on fused silica optical surface, the optimization of MRF processing parameters and the absorption characteristics of optics are investigated. First, the MRF processing parameters were determined by experimental method. Under the conditions of a wheel speed 200 rpm, flow rate 110 L/min, current 7.5 A, press depth 0.3 mm and polishing abrasive CeO2, the volumetric removal efficiency of removal function was relatively high, up to about 1.108 mm3/min. Appling the optimized parameters in small - size laser damage repairing process, no "comet tail" defects occurred on the optical surface. After MRF repairing process, the surface roughness was restored by immersed CCOS (computer control optical surfacing) technique. For immersed CCOS process, it contained two stage: coarse polishing and fine polishing. With 120 min of coarse polishing and 40 min of fine polishing, the roughness Ra decreased from the initial 6.179 nm to 0.7 nm, which was basically restored to the initial state. Finally, the photo - thermal absorption of the optics before and after repairing process was detected on a weak absorption testing platform. The results showed that the surface absorption decreased from the initial 425.38 ppm to 125.92 ppm, and the laser energy absorption of the repaired fused silica optics was significantly reduced, which verified the validity of the combined process of MRF and immersed CCOS process. In a conclusion, the research results in this paper can provide important technical support for the rapid repairing of small - size laser damage on fused silica optical surfaces, which was conducive to improving the service life of high - power laser systems.
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