Abstract
Ptychography is a coherent diffractive imaging method that can provide a diffraction-limited, robust reconstruction of the sample's complex transmission function without the use of high-quality optics. However, the scanning nature of conventional X-ray ptychography unavoidably requires the mechanical motion of either the illumination probe or the sample. In order to avoid overhead related to breaking and acceleration for every scan position, so-called fly-scan methods were developed. Here, we present an improved variant that removes the limitation of continuous scanning along a linear scanning path and allows for ptychographic reconstruction of scans taken along an arbitrary 2D continuous trajectory. We also demonstrate numerically and experimentally that our method provides significantly improved robustness against noise, particularly for larger fly-scan steps, i.e. sample shift during an exposure, which will gain importance with the advent of 4th generation synchrotron sources, where the available coherent flux may be increased by orders of magnitude. Finally, we show that the use of a spiral scan continuous trajectory alleviates significantly raster grid artifacts.
Highlights
Upcoming 4th generation synchrotron sources [1] are going to provide significantly increased brightness and, in combination with more efficient X-ray optics, potentially lead to thousand-fold increase in coherent flux [2]
The ptychography reconstruction can be seen as an optimization task that seeks a common illumination probe Pr and a common complex-valued transmission function Or in order to minimize the difference between the expected diffraction intensity Iie,k and the measured photon distribution Iim,k for all scan positions, where r and k are the set of 2D Cartesian coordinates perpendicular to the probe propagation direction in real and reciprocal space, respectively
We have demonstrated that our new variation of the fly-scan ptychography called arbitrary-path fly-scan (A-fly) method provides better reconstruction quality than the common fly-scan method at the same imaging dose or equivalently same reconstruction quality with longer step size
Summary
Upcoming 4th generation synchrotron sources [1] are going to provide significantly increased brightness and, in combination with more efficient X-ray optics, potentially lead to thousand-fold increase in coherent flux [2]. The idea of fly-scan ptychography is based on recording far-field diffraction patterns during the continuous motion of the sample This acquisition strategy works well provided that the motion during the acquisition does not exceed a handful of resolution elements. We introduce an alternative approach to fly-scan ptychography that explicitly uses the prior knowledge of the trajectory of the probe across the object and avoids the reconstruction of additional illumination modes. This improves its robustness to noise and allows the use of an arbitrary path in 2D
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