Silicon pore optics: a highly configurable modular x-ray mirror technology

Abstract

Silicon Pore Optics (SPO) was developed for light-weight X-ray telescopes with a large collecting area. Using technology from the semiconductor industry, thin mirror plates are produced from silicon wafers, and combined into modules. A large number of co-aligned modules forms the aperture. SPO enables ESA's next-generation flagship observatory NewAthena. In addition, it offers a large degree of customization. We discuss how SPO can be optimized for a mission by altering the properties of the plates and the configuration of the modules. This includes the membrane thickness and the spacing of the support-ribs of the plates. Multi-layer coatings optimize the effective area as a function of photon energy. A challenge is presented by the fixed height of the ribs, which is set by the thickness of the wafers from which the plates are made. For telescopes with a relatively short focal length, the fixed height leads to short mirror plates. Nevertheless, with a large number of modules, the total effective area may still be substantial. An avenue for future development could be to double the rib height. In addition to the properties of the mirror plates, the placement of the modules is customizable as well. For NewAthena, the modules are arranged in concentric rings, as an approximation of nested shells. On the other hand, the proposed NASA mission Arcus places its SPO modules in two sections ("petals"), which yield a substantially reduced cross-PSF. Therefore, the configurability of SPO makes it an attractive Xray optics technology for a wide range of applications.