In-Process Metrology For X-Ray Optics

Space-based astronomy at x-ray wavelengths has steadily progressed over the past 25 years. These advances have been made possible through the use of telescopes with increasingly higher resolution and collecting area, along with corresponding improvements in detectors, focal plane instrumentation, and pointing systems. In this paper, we discuss an in-process metrology system designed to provide sufficiently accurate data to the polishing process to allow fabrication of a half-arc second glancing angle of incidence telescope operating in the 1 to 7 KeV spectral region. This measurement system was developed in anticipation of, and applied to, the Advanced X-ray Astrophysics Facility (AXAF) Technology Mirror Assembly(TMA). The metrology instruments represent a considerable advance in the state of the art for measurements of large, thin, aspheric cylindrical optical elements. They allowed measurement of surface figure errors over a very wide range of spatial surface frequency with unprecedented accuracy during each phase of fabrication -- from coarse grinding through figuring and final polishing.