Fabrication of monocrystalline silicon x-ray mirrors

Abstract

Progress within the field of x-ray astronomy depends on astronomical x-ray observations of ever-increasing quality and speed. Fast and high-resolution x-ray observations over a broad spectral range promise amazing new discoveries. These observations, however, require a spaceborne x-ray telescope of unprecedented imaging power. Of the numerous technological concerns associated with the design and construction of such a telescope, the x-ray focusing optics present a particularly complex and arduous set of challenges. An x-ray optical assembly comprises many thousands of x-ray mirrors, a most critical element. Our group at NASA Goddard Space Flight Center (GSFC) pursues the development of an x-ray mirror manufacturing process capable of meeting the stringent quality, production time, and cost requirements of the next-generation of x-ray telescopes. The manufacturing process employs monocrystalline silicon: a lightweight, stiff, thermally conductive, and readily available material which is free of internal stress; it is a nearly ideal material for a thin mirror substrate. The process involves various traditional optical fabrication techniques adapted to x-ray mirror geometry. Presently, our process is capable of fabricating sub-arcsecond half-powerdiameter (HPD) resolution mirror pairs (primary and secondary) at a mirror thickness of 0.5 mm and of virtually any x-ray optical design (e.g. Wolter-I, Wolter-Schwarzschild, etc.). The mirror substrate surface quality is comparable to, and sometimes exceeding, that of the mirrors on the Chandra X-ray Observatory. This paper describes the various manufacturing steps involved in the production of x-ray mirror substrates and a present status report.

Performance Testing of a Large-Format X-ray Reflection Grating Prototype for a Suborbital Rocket Payload

“…The mirrors are produced from a block of single-crystal silicon, which allows them to theoretically be manufactured free of internal stresses for improved mirror performance. Further details of the mono-crystalline silicon mirror manufacture and alignment processes can be found in Riveros et al (2019) and Chan et al (2019). This technology is currently being studied for missions such as Lynx (Gaskin et al, 2018;Zhang et al, 2019a), AXIS (Mushotzky, 2018), HEX-P (Madsen et al, 2019), STAR-X (McClelland, 2017), and FORCE (Nakazawa et al, 2018).…”

Structural analysis and testing of silicon x-ray mirror modules

“…Individual mirror substrates, Figure 1-1, have been produced to exceptional sub-arcsecond quality [2] using a precision polishing process that is compatible with mass production [3]. The baseline size of the mirrors is 100mm by 100mm, with a thickness of 0.5mm.…”

Mass manufacturing of high resolution and lightweight monocrystalline silicon x-ray mirror modules

“…Polished substrates that meet optical requirements and have well defined fabrication steps are currently being produced to support technology development at the segment coating and module level. 4,5 Figure 3 shows a high level view of the fabrication steps. Segment coating to increase X-ray reflectivity, including coating stress compensation approaching the quality requirement specified in the Lynx error budget, has been demonstrated in a laboratory environment.…”

“…Despite the young age of substrate fabrication using polished silicon, our current set of machines and technicians can take commercially available blocks of silicon on Monday and deliver polished substrates by Friday that approach or exceed the quality of the best polished X-ray mirrors, currently in use on Chandra. 2,5 To highlight current efforts at developing mass production versions of our fabrication steps, we are outfitting a commercial computer numerically controlled (CNC) machine to light-weight more than one segment at a time, which takes place with little operator oversight once the process is started. Additional parts are prepared in advance and machine downtime to swap in new parts is minimal.…”