Development of micro-pore optics for x-ray applications

With Photonis and cosine Research BV, ESA has been developing and testing micro pore optics for x-ray imaging. Applications of the technology are foreseen to reduce mass and volume in, for example, a planetary x-ray imager, x-ray timing observatory or high-energy astrophysics. Photonis, a world leader in the design and development of micro pore optics, have developed a technique for manufacturing square channel pores formed from extruded glass fibres. Single square fibres, formed with soluble glass cores, are stacked into a former and redrawn to form multifibres of the required dimension. Radial sectors of an optic are then cut from a block formed by stacking multifibres and fusing them to form a monolithic glass structure. Sectors can be sliced, polished, etched and slumped to form the segment of an optic with specific radius. Two of these sectors will be mounted to form, for example, a Wolter I optic configuration. To improve reflectivity of the channel surfaces coating techniques have also been considered. The results of x-ray tests performed by ESA and cosine Research, using the BESSY-II synchrotron facility four-crystal monochromator beamline of the Physikalisch-Technische Bundesanstalt (PTB), on multi-fibres, sectors and slumped sectors will be discussed in this paper. Test measurements determine the x-ray transmission and focussing characteristics as they relate to the overall transmission, x-ray reflectivity of the channel walls, radial alignment of the fibres, slumping radius and fibre position in a fused block. The multifibres and sectors have also been inspected under microscope and Scanning electron Microscope (SEM) to inspect the channel walls and determine the improvements made in fibre stacking.