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The coherence requirements for efficient operation of an X-ray grating interferometer are discussed. It is shown how a Talbot-Lau geometry, in which an array of equidistant secondary sources is used, can be used to decouple fringe visibility in the interferometer (and thus, its efficiency) from the total size of the X-ray source. This principle can be used for phase-contrast radiography and tomography with sources of low brilliance, such as X-ray tubes.
Weitkamp et al. (Thu,) studied this question.