Optical-correction technique makes lambda/1000 optics a reality

摘要

A novel deposition method moves the substrate behind a patterned mask during deposition to achieve high control of thickness and subnanometer accuracy of optical thin-film correction. With the growing interest in ultrahigh-precision optics for such diverse purposes as astronomical imaging, gravity-wave observatories, subnanometer optical metrology, extreme-UV lithography, and x-ray optics, demand is increasing for optical components that have unprecedented quality at all levels, from microroughness to overall shape or "figure." While either superlative surface-microroughness values or a highly controlled figure can be achieved independently with superpolishing or single-point surface finishing techniques respectively, it is difficult to achieve both simultaneously. At CSIRO's Division of Industrial Physics, we have recently developed a technique that is capable of correcting the figure of optical components to subnanometer levels without degrading the microroughness. The technique was initially developed to correct optical-thickness variations of large-aperture Fabry-Perot etalon filters used for solar observation, but is applicable to any transmissive or reflective optical component. For transmissive optics, it is important to deposit material that is index-matched to the substrate; for example, we use tantalum pentoxide to correct lithium niobate and silicon dioxide for silica-based optics. For reflective optics, it is not necessary to index-match the corrective layer and any mechanically suitable material can be used.