Dresden 2017 – wissenschaftliches Programm

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MI: Fachverband Mikrosonden

MI 7: Poster: Microanalysis and Microscopy

MI 7.3: Poster

Mittwoch, 22. März 2017, 18:00–20:00, P4

Simulation and Reconstruction of Coherent Modes for Near Field Imaging — •Johannes Hagemann and Tim Salditt — Institut für Röntgenphysik, Friedrich-Hund-Platz 1, University Göttingen, 37077 Göttingen

In X-ray near field imaging experiments the probing beam determines the imaging quality in terms of resolution and artifacts. Distortions in the probe from optical elements such as focusing optics can easily spoil quantitative contrast. Thus characterizing the probe is an important issue. In previous work [1] we have reconstructed the probe under the assumption of full coherence. In this contribution we extend the reconstruction scheme to include also the partial coherent case, by extending the ptychography approach proposed for far field detection [2] to the near field. The reconstruction scheme uses the measurements from multiple detection planes. Experimentally this is achieved by moving the detector to different distances. The reconstruction is numerically quite demanding since the modes have to be individually propagated and orthogonalized in each iteration of the reconstruction algorithm. Without the use of GPUs this would be a time consuming process. By numerical simulations and a suitable representation of modes, we show how to take into account partial spatial coherence, both in image formation and in reconstruction. Our results show that the occupation numbers of the modes and the degree of coherence can be reconstructed.
[1] J. Hagemann et al., J. Synchrotron Radiat., (in review).
[2] P. Thibault, A. Menzel, Nature 494, 68-71(2013).