Strain analysis by inversion of coherent Bragg X-ray diffraction intensity: the illumination problem

Bragg coherent X-ray diffraction imaging is demonstrated with a micro-focused illumination. The 2D projected density of the 3D nano-crystal is successfully retrieved from the inversion of its diffraction intensity pattern. The analysis of the phase field at the sample position, which holds in principle the strain information, emphasizes the high sensitivity of the technique with regard to the wavefront structure. The ptychography approach is a proposed solution to discriminate the wavefront function from the sample electron density distribution. It is based on a redundancy of the collected information obtained by measuring a series of diffraction patterns for different but overlapping beam positions onto the sample. Applicability to the Bragg geometry still needs to be demonstrated.