Composite process for low contamination and high laser damage threshold processing of fused silica optics

Although chemical mechanical polishing (CMP) with the ceria slurry can achieve excellent surface figure accuracy, its inherent chemical activity often introduces metallic impurities that are difficult to remove, creating a bottleneck that limits the laser damage performance of optical components. We compared for the first time systematically the differences in metallic impurity content on glass surfaces after the ceria and silica sol polishing. It also verified the effectiveness of acid cleaning and ion beam treatment in removing shallow contaminants and confirmed that intrinsic hydroxyl impurities during acid cleaning do not affect glass surface stress and roughness. Based on this, a composite process route was proposed: first, using inert and easily cleanable silica sol for the main polishing; then, thoroughly purifying the surface through acid cleaning; and finally, applying simple postpolishing to eliminate any microdefects potentially introduced by acid cleaning and to utilize ion beam figuring to achieve the ultimate smooth surface. The results confirmed that the composite process can reduce metallic impurity content to the ppb level and increase the laser-induced damage threshold by 27.2% compared with the conventional process. We provide an important reference for the low-contamination, high laser damage threshold processing technology of fused silica components.