Nanofocusing optics for synchrotron radiation instrumentation

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This proposal requests manpower and facilities to develop a novel type of X-ray lens that will have a major impact in the study of nano-scale materials. The unprecedented brilliance achieved by 3rd generation synchrotron sources has opened up new opportunities for the study of materials at the nanometre scale. It will have a huge impact on a wide area of research including environmental science, catalysis and biology. The key to the exploitation of the improved sources is the development of novel optics that focus the narrow beams without loss of their brilliance and coherence. Grazing angle mirrors are widely used, but because of the grazing angle (few milliradians) the photon beam is particularly sensitive to slope errors, and roughness. Developments beyond current state-of-the-art are limited and expensive. New devices have been proposed that rely on refraction and diffraction. These include compound refractive lenses (CRL's) and kinoform lenses. CRL's are obtained by pressing the material with very hard parabolic tools, and then assembling several lenses together to reach the desired focus at the chosen energy. Aluminium and beryllium CRL's are routinely used in other synchrotrons and the good lateral resolution obtained with Be CRL's makes them even suitable for imaging. Focused spots of few tens of nanometers have been demonstrated with new refractive micro fabricated silicon planar lens, which can be more accurate in shape than simple pressed Al or Be lenses. The Optics Group at Diamond and the collaborators in this project aim at improving and enlarging the UK know-how on design and fabrication of nanofocusing lenses and routinely provide microfocusing lenses at lower cost than mirrors. Silicon planar low absorption kinoform lenses have been fabricated and successfully tested by the group, using a modest grant from the Centre for Instrumentation. A microfocused spot was obtained with these lenses at a photon energy of 12 keV. The data show short focus tails and absence of background. There is much scope for improvement and we believe that if this project is successful, UK synchrotron users will have access to the best in-line focusing optics. With this proposal we request resources for improving acceptance of the microfocus lenses and to achieve nanofocusing. In addition to silicon single crystal, we wish to use other lens materials like CVD diamond, germanium and nickel. Different materials are infact needed to cover a large photon energy range. CVD diamond, moreover, has the best performance in terms of power load and low absorption. Practical exploitation of these lenses in beamlines will require special arrangements. A single planar refractive lens produces a line focus: in order to produce a point focus two wafers have to be held at the right positions and mutual orientation, therefore special holders and motorised stages have to be envisaged. Monitoring and alignment of instrumentation with nanometre precision will be developed and tested on synchrotron beamlines. Finally, we wish to reply to the board request that 'The full proposal should include how many users will benefit from this development and how the new equipment differs from similar equipment being developed elsewhere e.g. at the ESRF'. We highlight in the support case that the ESRF has developed focusing and collimating optics based on mirrors and multilayers. The refractive optics proposed here have been developed by other laboratories (Aachen University, Paul Scherrer Institute) and only tested at the ESRF. Nanofocusing lenses have been demonstrated but not brought to full exploitation. Beams of 50 nm are achieved under special conditions at very few beamlines. Lenses fabricated in these laboratories will not be available to UK users for a long period because they are not for purchase (apart from the Be and Al lenses which are not nanofocusing devices).We aim at providing these on a daily basis to the 50% of UK users.