Crystal tilt error and its correction in diffraction enhanced imaging system

In the experimental setup for Diffraction Enhanced Imaging (DEI) and its extension, Multiple-Image Radiography (MIR), it is essential to have the two or three crystals angularly aligned relative to one another around two orthogonal axes; the angle around an axis perpendicular to the diffraction plane (the Bragg angle) and also around a perpendicular axis in the plane (azimuthal angle). The appearance of the azimuthal angle (tilt error) will complicate the interpretation of the DEI/MIR images by creating a systematic change in the Bragg angle across the width of the imaging beam which in turn creates intensity variations across the imaging field. In this paper we present the effect of a tilt error, its estimation from the resulting images, and a method to correct such an error for the DEI/MIR images. The analysis and results will also apply to multiple crystal systems with tilt errors, such as monochromators on synchrotron beamlines.