Surface characteristics of an optical component manufactured with a polyurethane lap

Some interesting small pits/depressions on the surface of optics polished by a polyurethane pad are shown and possible reasons for the pits are analyzed. These small pits may appear regardless of the material, size, and shape of the optical component. The depth of the pits/depressions varies from <0.1lambda (lambda=632.8 nm) to >0.5lambda and the diameters lie in the range from approximately 1 to approximately 3 mm. The reasons the pits/depressions form are discussed; in the meantime, some methods to make them shallow are proposed. The pits/depressions greatly influence the integrity of optics and, therefore, may deteriorate the performance of optical components.