Abstract
The segmented approach in the design of grazing incidence X-ray optics has been utilized in constructing conical foil mirrors for several missions such as BBXRT, ASCA, as well as the failed mission Astro-E. The advantages include lightweight construction, a large collecting area, and broadband response in the X-ray band. A key weakness, which places these mirrors increasingly at a disadvantage with regard to other high throughput mirrors, e.g., those used for XMM, is a spatial resolution considerably worse than limits imposed by the geometry. Our first major breakthrough in addressing this problem was the introduction of surface replication, a technique which transfers the smooth surface of glass mandrels onto conical aluminum foil segments via a thin epoxy buffer layer. More recently we have made a concerted effort to evaluate the remaining spatial error, still well above that expected from the approximate geometry. We investigated the major error terms that include the curvature error of the reflectors along the axial direction, roundness error along the circumference of reflectors, and positioning error of the reflectors in the supporting structure. This effort leads to an improved overall angular resolution for such quadrant-segmented systems. Positioning error is reduced by reduction in the distortion of the two-stage telescope housings with new reflector alignment and mounting techniques. We report the current status in the improvement of angular resolution in the segmented foil optics and our understanding of remaining errors.
