Aberration-free silicon pore x-ray optics

Silicon Pore Optics is an enabling technology for future L- and M-class astrophysics X-ray missions, which require high angular resolution (~5 arc seconds) and large effective area (1 to 2 m2 at a few keV). The technology exploits the high-quality of super-polished 300 mm silicon wafers and the associated industrial mass production processes, which are readily available in the semiconductor industry. The plan-parallel wafers have a surface roughness better than 0.1 nm rms and are diced, structured, wedged, coated, bent and stacked to form modular Silicon Pore Optics, which can be grouped into a larger optic. The modules are assembled from silicon alone, with all the mechanical advantages, and form an intrinsically stiff pore structure. The optics design was initially based on long (25 to 50 m) focal length X-ray telescopes, which could achieve several arc second angular resolution by curving the silicon mirror in only one direction (conical approximation). Recently shorter focal length missions (10 to 20 m) have been discussed, for which we started to develop Silicon Pore Optics having a secondary curvature in the mirror, allowing the production of Wolter-I type optics, which are on axis aberration-free. In this paper we will present the new manufacturing process, the results achieved and the lessons learned.