Nanoscale ion beam polishing of optical materials

A method of ion beam polishing is described, the special features of which consist in (i) preferential ion beam assisted deposition of a nanometer-thick layer into depressions of the initial relief by oxygen-ion sputtering of a target with a composition identical to that of the processed object; (ii) sputtering of the resulting surface structure by a normally incident low-energy oxygen ion beam to a depth reaching approximately two layers of the deposited material; and (iii) deposition-sputtering cycles repeated with gradually decreasing thickness of the deposited layer until the necessary final state of the surface is attained. Examples of the surface of quartz, sitall (glass ceramic), and BK-7 optical glass processed using the proposed ion beam polishing method show a more than twofold decrease in the height of the relief protrusions as compared to that on the initial surface. On the ion beam processed quartz surface areas with dimensions 2.5×2.5 μm, the maximum roughness height did not exceed 0.8 nm.