Ion polishing with the aid of a planarizing film.

An ion polishing technique employing a planarizing film in conjunction with ion-beam erosion at the planarizing angle was used to remove surface irregularities associated with conventional polishing of optical surfaces. By maintaining a planar surface throughout the erosion process, nonuniform erosion resulting from faceting, redeposition, and ion reflection is eliminated. Smooth surfaces on fused quartz are obtained by erosion of a planarizing film of photoresist at an angle of 60 degrees. The method is applicable to a wide variety of materials and may be useful for removing the surface roughness limitation on the laser-induced damage threshold of optical surfaces.