X-ray focusing using an inclined Bragg-reflection lens

An experimental demonstration showing that a one-dimensional focus can be produced by using the principle of inclined diffraction from a perfect crystal is presented. By machining a groove with a controlled cross-sectional profile it is shown that it is possible to vary the out-of-plane deviations in a controlled manner and hence generate a focus. Also demonstrated is the use of four reflections in (-,+,+,-) dispersive geometry resulting in the cancellation of all beam-spreading in the orthogonal direction. The experiment used an energy of 15 keV with a source-to-crystal distance of 13.5 m and crystal-to-focus distance of 4.5 m. A focus of width 0.29 mm was produced from an incident beam of width 2.7 mm. It is clear from the measurements that a better surface finish would result in a smaller focal spot.