Polishing study using Teflon and pitch laps to produce flat and supersmooth surfaces

Teflon polishing is compared with pitch polishing as a method for achieving supersmooth and flat optical surfaces. Because a Teflon lap wears slowly, it will retain its surface shape to produce extremely flat optical surfaces, lambda/100, consistently and reliably for extended periods of time, of the order of days. To compare the two methods, we polished 50-mm-diameter samples of various optical materials, using colloidal suspensions in water on both pitch and Teflon laps under the same polishing conditions. Flatness was maintained to better than lambda/10, and roughness less than 10 A rms was measured on all samples by two Talystep surface-profiling instruments, one in the United States and one in Australia, with excellent agreement between measurements made by the two instruments. It was possible to obtain flat andsmooth surfaces (<4-A rms roughness) on all materials (except for F4, flint glass), but only certain combinations of material, abrasive, and lap could be used to give the correct polishing conditions and s rface chemistry.