A two-stage replication technique has been developed that will enable microroughness measurements to be made on large or unusually shaped optics that cannot be measured using existing techniques. A small, first-stage replica of room-temperature-vulcanizing (RTV) silicone rubber is made of one or more parts of the surface. This material exactly replicates surface details and separates easily from most glass and metal optics. A second-stage epoxy replica is then made from the first-stage replica. It also preserves surface details and can be easily separated from the first-stage replica. The epoxy replica can be aluminized for Nomarski microscope examination, interferometric or scattering measurements, and can also be profiled with a diamond stylus probe. Examples are given of various types of surfaces and their replicas. Surface profiles are also shown of two masters and their replicas. This two-stage replication technique has been found to give excellent replication of surface detail, along with adequate preservation of surface flatness and a minimum lateral dimensional change, 0.3%. It is thus an excellent method for sampling small surface areas of large optics.
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