Ptychography with a Virtually Enlarged Illumination

F. Wittwer, R. Hoppe, F. Seiboth, J. Reinhardt, M. Scholz, C. G. Schroer
2018 Microscopy and Microanalysis  
Ptychography has become a key tool for high-resolution X-ray microscopy. We present here an extension to it that allows to work with insufficiently sampled diffraction patterns and reconstructs previously unseen parts of the sample. In ptychographic imaging the sample is scanned through a coherent beam recording the intensity distribution of the transmitted scattered wavefield at each scanpoint. Based on the ensemble of diffraction patterns and redundant information in adjacent diffraction
more » ... rns, ptychography retrieves the complex-valued transmission function of the sample. At the same time, also the illuminating probe is reconstructed in amplitude and phase. Due to this, the ptychography reconstructions are independent of any aberrations from the optics and the spatial resolution is not limited by the numerical aperture of the optics. Today, resolutions in the hard X-ray regime of 30 nm down to 10 nm are routinely achieved. One of the most popular ptychographic algorithms, ePIE [1], now has many extensions to deal with different experimental conditions, for example for thick, non-planar objects a multislice variant was proposed [2]. One extension concerns the influence of the detector on the measured diffraction patterns. A detector pixel integrates the number of photons over its area. A speckle can only be properly sampled, if it extends over multiple pixels. When the speckles are of the same size or smaller than a pixel, the sampling theorem is not fulfilled resulting in loss of information that leads to artefacts in the reconstruction. The up-sampling ptychographic iterative engine (sPIE), however, is able to reconstruct sample and probe even when the speckle are smaller than one pixel [3] . Due to the reciprocal relationship between distances in the sample plane and the detector plane and accordingly between the size of the probe and the resulting speckles, small speckles correspond to a large probe and vice versa. We demonstrate that sPIE can be used for aberrated focusing optics, which produce a larger-than-designed probe, and that this larger probe allows for the reconstruction of hitherto unseen parts of the sample outside of the original field of view.
doi:10.1017/s1431927618012667 fatcat:52tluvsqqrgnvjpsk6emokaqsm