Direct fabrication of full-shell x-ray optics

Abstract

Material Density (g/cm 3 ) CTE (10 -6 / K -1 ) Elastic Modulus GPa Yield Strength MPa Fused Silica 2.2 0.5 72 48* Beryllium 1.8 12 318 240 Al (6061) 2.7 24 69 276 AlSi 2.8 17 90 235

Development of a direct fabrication technique for full-shell x-ray optics

“…Two major challenges for this technology are to provide adequate support to the mirror substrates during all production steps and to figure the mirror without introducing additional mid-spatial frequency errors. In our previous paper we had presented the design of the fixtures aimed to support the mirrors during diamond turning, polishing and metrology [6]. The development of the polishing technique for direct fabrication of the x-ray optics is in progress.…”

“…For thin-shell direct fabrication, one of the major challenges is to support the shell during diamond turning polishing and metrology so that, at one extreme, it cannot microyield, but also cannot deflect enough to affect the polishing itself. The design of the fixtures to support the shells during processing have already been described [6]. While the fixtures were in fabrication, efforts were concentrated on the development of polishing processes using the Zeeko polishing machine.…”

“…One of the techniques under development at Goddard Space Flight Center uses segmented substrates made from crystalline silicon [3], the other utilizes the full-shell approach. The latter utilizes substrates from fused silica (Astronomical Observatory of Brera, Italy) [4,5] or metal [6] (Marshall Space Flight Center.) This approach capitalizes on modern methods of figuring and polishing the mirrors with low surface errors but requires thicker substrates than mirrors fabricated from replication techniques.…”

Technologies for advanced X-ray mirror fabrication

“…The footprint for a given time period is defined by: the geometric environment of the bonnet (precession angle, offset to the surface), the dynamic environment of bonnet in contact with the optical surface (rotation, translation), and the physical environment (slurry concentration and polishing cloth) -Figure 7. The resulting tool-path of the bonnet is unique to the optical surface and therefore accurate indexing of the optical surface to the bonnet is necessary [24]. Robotic polishing has been used to process X-ray mirrors both directly and indirectly.…”