Near-field ptychography using lateral and longitudinal shifts

Abstract

Image reconstruction of in-line holography depends crucially on the probing wave front used to illuminate an object. Aberrations inherent to the illumination can mix with the features imposed by the object. Conventional raw data processing methods rely on the division of the measured hologram by the intensity profile of the probe and are not able to fully eliminate artifacts caused by the illumination. Here we present a generalized ptychography approach to simultaneously reconstruct object and probe in the optical near-field. Combining the ideas of ptychographic lateral shifts of the object with variations of the propagation distance by longitudinal shifts, simultaneous reconstruction of object and probe was achieved equally well for a highly aberrated and a mildly disturbed probe without the need for an additional wave front diffuser. The method overcomes the image deterioration by a non-ideal probe and at the same time any restrictions due to linearization of the object's transmission function or the Fresnel propagator. The method is demonstrated experimentally using visible light and hard x-rays, in both parallel beam and cone beam geometry, which is relevant for high resolution x-ray imaging. It also opens up a new approach to characterize extended wave fronts by phase retrieval.

X-Ray Near-Field Holography: Beyond Idealized Assumptions of the Probe

“…decay of the probe at the holography end station GINIX (Göttingen Instrument for Nano-Imaging with X-rays) [2,66] at the P10 beamline of Petra III (DESY, Hamburg), and use it for reconstruction based on an improved multiple magnitude projections (MMP)-scheme [53,67,68] as well as the near-field ptychography (NFP)-scheme [14]. We recorded two independent data sets: One for NFP with the afore-mentioned lateral and longitudinal shifts of an object with a fixed focus to detector distance.…”

“…The validity of such assumptions has recently been investigated, showing that they lead to reduced resolution and image quality [53,54]. Aiming at more appropriate schemes to treat the data, recent work has introduced the concept of simultaneous reconstruction of probe and object to near-field (propagation) imaging [13,14]. This was achieved by a suitable generalization and extension of the ptychographic algorithms initially developed for confined beams (typical for far-field diffractive imaging) [59][60][61][62][63][64].…”

“…Thus, the wavefront modified and not the 'natural' probe of the setup is recovered. Contrarily, [14] used the diversity generated by lateral and longitudinal shifts of the object in the beam to recover the natural probe of the setup along with the object. Since beam reconstruction in one plane gives access to the wavefront in all other planes, based on numerical propagation, one may wonder why a near-field reconstruction is needed at all.…”

“…At the same time, we are interested in a complete characterization which also includes the field in the focal plane. This was previously not accessible, since in the data of [13,14] the FOV is cut out from the central part of the probe. This is not sufficient to obtain the complete information on the probe, i.e.…”

Three-dimensional single-cell imaging with X-ray waveguides in the holographic regime

“…Furthermore, the illumination needs to be well known in this regime in order to ensure meaningful phase reconstructions. If significant artifacts disturb the wavefront (probe), near-field ptychography can be used to reconstruct object and probe (Robisch et al, 2015;Stockmar et al, 2015), at the expense, however, of additional exposures and therefore also dose. This may limit the applicability to radiation-sensitive samples like biological tissue.…”