Optimisation of coherent X-ray diffraction imaging at ultrabright synchrotron sources

Coherent X-ray Diffraction Imaging (CXDI) is a powerful method of imaging single crystalline grains within a powder. Direct Fourier transformation of the oversampled diffraction pattern surrounding a Bragg peak is possible once the phases have been obtained using a 'support' constraint. The image is in general complex with the phase representing a projection of the atomic displacements allowing access to the internal strains inside the crystal. CXDI relies crucially on the production of a coherent beam of X-rays, which is one of tire technical advances of the latest 3rd generation Synchroton Radiation (SR) sources. It is shown here how the use of a secondary Source in the design of the X-ray beamline allows the coherence to be controlled continuously over a finite range without any loss of flux. The conclusions will have significant impact on instruments currently being designed at tire Diamond Light Source and the new National Synchrotron Light Source (NSLS-2).