Researchers at the Optical Sciences Center of the University of Arizona (Tucson, AZ) are exploring an alternative to conventional optical surface-polishing techniques. Using an orbital shaker, the new process imparts an oscillating x-y motion to a slurry comprising beads, a polishing compound, and water. One benefit is that the shape of the polishing implement sets fewer limits on the shape of the surface—for example, it may be possible to polish the inner surface of a hypersphere that cannot be polished conventionally due to the difficulty of inserting and driving a polishing tool.
The beads, which basically roll across the surface of the substrate to be ground or polished, can have several geometries, including spherical, irregular, or planar shapes. They also can be made from a variety of materials, with specifics depending on the optics material. For 25-mm-diameter, fused-silica samples, the researchers report the process produced average peak-to-valley nonuniformity (mostly power) on the order of 0.1 µm/day, with a material removal rate of 1.4 µm/day. The typical surface roughness was 3.5 nm after three days. Subsurface damage was removed in approximately 3.5 days without generating additional damage. Contact José Sasián at [email protected].