Divide and update: towards single-shot object and probe retrieval for near-field holography

Abstract

We present a phase reconstruction scheme for X-ray near-field holographic imaging based on a separability constraint for probe and object. In order to achieve this, we have devised an algorithm which requires only two measurements - with and without an object in the beam. This scheme is advantageous if the standard flat-field correction fails and a full ptychographic dataset can not be acquired, since either object or probe are dynamic. The scheme is validated by numerical simulations and by a proof-of-concept experiment using highly focused undulator radiation of the beamline ID16a of the European Synchrotron Radiation Facility (ESRF).

Evaluation of the Weighted Mean X-ray Energy for an Imaging System Via Propagation-Based Phase-Contrast Imaging

“…Thus, it can be assumed to be in the Fresnel regime and iterative reconstruction algorithms that are based on the Fresnel approximation can be applied [19,20]. For reconstructing the phase image of an object different phase retrieval algorithms [12,15,[21][22][23][24][25][26][27]] can be used. Propagation of a wave Ψ(x, y, z) in Fresnel diffraction can be modelled by the Fresnel propagator [23]…”

Single-pulse phase-contrast imaging at free-electron lasers in the hard X-ray regime

“…With highly performing phase retrieval schemes available, the current limits are still in the classical flat-field division itself (Homann et al, 2015). In future this could be circumvented by an algorithmic solution similar to Hagemann & Salditt (2017a), enhanced by the simultaneous reconstruction of modes (Hagemann & Salditt, 2017b). In other words, rather than reconstructing intensity PCA components and dividing object intensities by (synthesized) flat-fields, the algorithm would fully work in the space of complex-valued coherent modes.…”

“…Nevertheless, in order to separate contributions of the illuminating probe from the object, it is indispensable to perform the standard flat-field correction in holographic imaging as a necessary pre-processing step. Knowledge of the probe's complex wavefield, obtained by a suitable characterization scheme (Robisch et al, 2016;Hagemann & Salditt, 2017a), would allow to take propagation effects into account and thereby reducing the artifacts. Note that alternative schemes devised to smoothen out for example the stripes associated with focusing by Kirkpatrick-Baez mirrors (Hubert et al, 2018) require several exposures.…”

3d virtual histology of neuronal tissue by propagation-based x-ray phase-contrast tomography

“…However, in practice it is quite challenging to reconstruct the probe from the measurements and more elaborate acquisition or reconstruction schemes as, e.g., near-field ptychography including lateral and/or longitudinal shifts of the sample [143,160] or divide and update [62], have to be used.…”