Recent developments in profiling optical surfaces

To understand better the fabrication of optical surfaces and to be able to produce smoother, lower-scatter surfaces, we need to extend characterization techniques to shorter and longer surface spatial wavelengths beyond the conventional 1-µm to 1-mm region. Scanning probe microscopes are now available for profiling optical surfaces with height and lateral resolutions of a few atomic spacings. In this paper we report on measurements made with a Nanoscope II atomic force microscope on a variety of supersmoothoptical surfaces and compare these results with measurements made with a conventional stylus profiling instrument. Consistent results have been obtained. To cover the long-spatial-wavelength region, long-scan profilers can be used to measure surface waviness in the range from a few millimeters to a few centimeters with height sensitivities ~10 times better than conventional interferometers. The characterization of a Nanostep long-scan mechanical profiler is described, and examples of surface profiles taken on selected flat samples are given.