Lightweight X-ray Wolter optics with a high angular resolution will enable the next generation of X-ray telescopes in space. The International X-ray Observatory (IXO) requires a mirror assembly of 3 m<sup>2</sup> effective area (at 1.5 keV) and an angular resolution of 5 arcsec. These specifications can only be achieved with a novel technology like Silicon Pore Optics, which is developed by ESA together with a consortium of European industry.<p> </p>Silicon Pore Optics are made of commercial Si wafers using process technology adapted from the semiconductor industry. We present the manufacturing process ranging from single mirror plates towards complete focusing mirror modules mounted in flight configuration. The performance of the mirror modules is tested using X-ray pencil beams or full X-ray illumination. In 2009, an angular resolution of 9 arcsec was achieved, demonstrating the improvement of the technology compared to 17 arcsec in 2007. Further development activities of Silicon Pore Optics concentrate on ruggedizing the mounting system and performing environmental tests, integrating baffles into the mirror modules and assessing the mass production.
Silicon pore optics is a technology developed to enable future large area X-ray telescopes, such as the
International X-ray Observatory (IXO), a candidate mission in the ESA Space Science Programme 'Cosmic
Visions 2015-2025'. IXO uses nested mirrors in Wolter-I configuration to focus grazing incidence X-ray photons
on a detector plane. The IXO optics will have to meet stringent performance requirements including an effective
area of >2.5 m<sup>2</sup> at 1.25 keV and >0.65 m<sup>2</sup> at 6 keV and angular resolution better than 5 arc seconds. To achieve
the collecting area requires a total polished mirror surface area of ~1300 m<sup>2</sup> with a surface roughness better than
0.5 nm rms. By using commercial high-quality 12" silicon wafers which are diced, structured, wedged, coated,
bent and stacked, the stringent performance requirements of IXO can be attained without any costly polishing
steps. Two of these stacks are then assembled into a co-aligned mirror module, which is a complete X-ray
imaging system. Included in the mirror module are the isostatic mounting points, providing a reliable interface to
the telescope. Hundreds of such mirror modules are finally integrated into petals, and mounted onto the
spacecraft to form an X-ray optic of approximately 4 m in diameter.
In this paper we will present the silicon pore optics mass manufacturing process and latest X-ray test results of
mirror modules mounted in flight configuration.
Silicon pore optics are currently under development for missions such as the International X-ray Observatory (IXO) as
an alternative to the glass or nickel shell mirrors that were used in previous generation X-ray telescopes. The
unprecedented effective area requirement of the IXO requires a modular optics design suitable for mass production. In
this paper we discuss the current state-of-the-art in plate manufacturing technology. We provide examples of process
innovations that have directly impacted the cost per mirror plate and have reduced the manufacturing cost of a mirror
module. We show how a switch from silicon to silica as the reflective surface results in a simplified process flow without
a corresponding change in the optical performance. We demonstrate how standard photolithographic techniques, applied
in the semiconductor industry, can be used to pattern a reflective layer. The 5 arc-second angular resolution requirement
of the IXO has stimulated a theoretical analysis of engineering tolerances in relation to angular resolution. We prove that
improved control of the wedge angle by means of etch rate monitoring results in improved angular resolution. The
results of this investigation will be used as the basis for future development in design for mass production.
Future X-ray astrophysics missions, such as the International X-ray Observatory, IXO, require the development of novel
optics in order to deliver the mission's large aperture, high angular resolution and low mass requirements. A series of
activities have been pursued by ESA, leading a consortium of European industries to develop Silicon Pore Optics for use
as an x-ray mirror technology.
A novel process takes as the base mirror material commercially available silicon wafers, which have been shown to
possess excellent x-ray reflecting qualities. These are ribbed, curved and stacked concentrically in layers that have the
desired shape at a given radii of the x-ray aperture. Pairs of stacks are aligned and mounted into doubly reflecting mirror
modules that can be aligned into the x-ray aperture without the very high angular and position alignment requirements
that need to be achieved for mirror plates within the mirror module. The use of this silicon pore optics design
substantially reduces mirror assembly time, equipment and costs in comparison to alternative IXO mirror designs.
This paper will report the current technology development status of the silicon pore optics and the roadmap expected for
developments to meet an IXO schedule. Test results from measurements performed at the PTB lab of the Bessy
synchrotron facility and from full illumination at the Panter x-ray facility will be presented.