319 research outputs found
Advanced Denoising for X-ray Ptychography
The success of ptychographic imaging experiments strongly depends on
achieving high signal-to-noise ratio. This is particularly important in
nanoscale imaging experiments when diffraction signals are very weak and the
experiments are accompanied by significant parasitic scattering (background),
outliers or correlated noise sources. It is also critical when rare events such
as cosmic rays, or bad frames caused by electronic glitches or shutter timing
malfunction take place.
In this paper, we propose a novel iterative algorithm with rigorous analysis
that exploits the direct forward model for parasitic noise and sample
smoothness to achieve a thorough characterization and removal of structured and
random noise. We present a formal description of the proposed algorithm and
prove its convergence under mild conditions. Numerical experiments from
simulations and real data (both soft and hard X-ray beamlines) demonstrate that
the proposed algorithms produce better results when compared to
state-of-the-art methods.Comment: 24 pages, 9 figure
Solving ptychography with a convex relaxation
Ptychography is a powerful computational imaging technique that transforms a
collection of low-resolution images into a high-resolution sample
reconstruction. Unfortunately, algorithms that are currently used to solve this
reconstruction problem lack stability, robustness, and theoretical guarantees.
Recently, convex optimization algorithms have improved the accuracy and
reliability of several related reconstruction efforts. This paper proposes a
convex formulation of the ptychography problem. This formulation has no local
minima, it can be solved using a wide range of algorithms, it can incorporate
appropriate noise models, and it can include multiple a priori constraints. The
paper considers a specific algorithm, based on low-rank factorization, whose
runtime and memory usage are near-linear in the size of the output image.
Experiments demonstrate that this approach offers a 25% lower background
variance on average than alternating projections, the current standard
algorithm for ptychographic reconstruction.Comment: 8 pages, 8 figure
py4DSTEM: a software package for multimodal analysis of four-dimensional scanning transmission electron microscopy datasets
Scanning transmission electron microscopy (STEM) allows for imaging,
diffraction, and spectroscopy of materials on length scales ranging from
microns to atoms. By using a high-speed, direct electron detector, it is now
possible to record a full 2D image of the diffracted electron beam at each
probe position, typically a 2D grid of probe positions. These 4D-STEM datasets
are rich in information, including signatures of the local structure,
orientation, deformation, electromagnetic fields and other sample-dependent
properties. However, extracting this information requires complex analysis
pipelines, from data wrangling to calibration to analysis to visualization, all
while maintaining robustness against imaging distortions and artifacts. In this
paper, we present py4DSTEM, an analysis toolkit for measuring material
properties from 4D-STEM datasets, written in the Python language and released
with an open source license. We describe the algorithmic steps for dataset
calibration and various 4D-STEM property measurements in detail, and present
results from several experimental datasets. We have also implemented a simple
and universal file format appropriate for electron microscopy data in py4DSTEM,
which uses the open source HDF5 standard. We hope this tool will benefit the
research community, helps to move the developing standards for data and
computational methods in electron microscopy, and invite the community to
contribute to this ongoing, fully open-source project
System calibration method for Fourier ptychographic microscopy
Fourier ptychographic microscopy (FPM) is a recently proposed quantitative
phase imaging technique with high resolution and wide field-of-view (FOV). In
current FPM imaging platforms, systematic error sources come from the
aberrations, LED intensity fluctuation, parameter imperfections and noise,
which will severely corrupt the reconstruction results with artifacts. Although
these problems have been researched and some special methods have been proposed
respectively, there is no method to solve all of them. However, the systematic
error is a mixture of various sources in the real situation. It is difficult to
distinguish a kind of error source from another due to the similar artifacts.
To this end, we report a system calibration procedure, termed SC-FPM, based on
the simulated annealing (SA) algorithm, LED intensity correction and adaptive
step-size strategy, which involves the evaluation of an error matric at each
iteration step, followed by the re-estimation of accurate parameters. The great
performance has been achieved both in simulation and experiments. The reported
system calibration scheme improves the robustness of FPM and relaxes the
experiment conditions, which makes the FPM more pragmatic.Comment: 18 pages, 9 figure
Water Window Ptychographic Imaging with Characterized Coherent X-rays
We report on a ptychographical coherent diffractive imaging experiment in the
water window with focused soft X-rays at . An X-ray beam with
high degree of coherence was selected for ptychography at the P04 beamline of
the PETRA III synchrotron radiation source. We measured the beam coherence with
the newly developed non-redundant array method. A pinhole
in size selected the coherent part of the beam and was used for ptychographic
measurements of a lithographically manufactured test sample and fossil diatom.
The achieved resolution was for the test sample and only
limited by the size of the detector. The diatom was imaged at a resolution
better than .Comment: 22 pages. 7 figure
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