Figure 3

Reference phase-stepping scan without the sample in the beam. Top: The intensity profile. The detector is structured in 256 \(\times \) 256 pixel sub-units with a two pixel gap in-between. The structures on the active area result from the Cadmium-Telluride crystals of the detector as well as the gratings gaps of \(\text {G}_2\) in the beam (well visible on the phase map as sudden value shifts). A flat-field correction removes these features from the image. Center: The phase profile of the system. The phase is the offset of the phase stepping curve as described in Eq. (2). It is tuned to be as homogeneous as possible by aligning the gratings. Bottom: The visibility profile. The visibility is also obtained from Eq. (2) and characterizes the coherence of the system.