Robust, angstrom level circularity profilometry

摘要: The measurement of circularity cylindrical grazing incidence optics is a formidable task, because required fabrication accuracies are typically on the order several micro-inches, with resulting accuracies a micro-inch or less. Such demanding accuracy requirements have evolved as need for high resolution extreme ultraviolet and X-ray systems has increased. Current approaches involve rotating element (or one or more probes) about element's axis, sensing surface runout. Sensing can be mechanical or interferometric, but in either case approach clearly sensitive to runout rotation itself. Even when multiple probes used eliminate repeatable errors, nonrepeatable errors drifts probe position can severely degrade accuracy. In this paper we discuss new, noncontacting (patent pending) that involves measuring local circumferential curvature test piece by simultaneously measuring its slope at two slightly displaced locations. As pair beams scanned along circumference, profile curvature is built, from which deduced. not only makes insensitive to all types ofvibration drift (both height slope), also it insensitive runout errors relative rotation. Thus, achieve absolute orders magnitude smaller than typical runouts. We summarize special qualities make well suited measuring cylindrical optics, able accommodate radii small twenty millimeters, working the inside (concave) outside (convex) surface. Finally, some preliminary experimental results and compare them typical requirements.