Developments in glass micro pore optics for x-ray applications

ESA is developing technologies for x-ray imaging to reduce the mass and volume of future missions. Applications of x-ray optics are foreseen in future planetary x-ray imagers, x-ray timing observatories and in observatories for high-energy astrophysics. With reference to planetary x-ray imagers the use of glass micro-pore material is being investigated. This technology allows the formation of a monolithic, glass structure that can be used to focus x-rays by glancing reflections off the pore walls. A technique to form x-ray focusing plates that contain thousands of square micro-pores has been developed with Photonis. The square pores are formed in a process that fuses blocks of extruded square fibres, which can then be sliced, etched and slumped to form the segment of an optic with a specific radius. A proposed imager would be created from 2 optics, slumped with different radii, and mounted to form an approximation of a Wolter I optic configuration. Reflection can be improved by coating the channel surfaces with a heavy element, such as nickel. Continuing developments have been made to enhance the manufacturing processes and improve the characteristics of the manufactured x-ray focusing plates, such as improved surface roughness and squareness of pore walls, improved pore alignment from fibre stacking through to optic segment slumping and development of pore wall coatings. In order to measure improvements x-ray measurements are performed by ESA and cosine Research BV, using the BESSY-II synchrotron facility four-crystal monochromator beamline of the Physikalisch-Technische Bundesanstalt, on multifibres, sectors and slumped sectors. A probing beam is used to investigate a number of pores to determine x-ray transmission, focussing characteristics as they relate to the overall transmission, x-ray reflectivity of channel-walls, radial alignment of fibres, slumping radius and fibre position in a fused block. SEM measurements and microscope inspection have also been used to inspect the channel walls and determine improvements made in fibre stacking and coating.