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Open Access
Abstract: Spectral computed tomography has received considerable interest in recent years since spectral measurements contain much richer information about the object of interest. In spectral computed tomography, we are interested in the energy channel-wise reconstructions of the object. However, such reconstructions suffer from a low signal-to-noise ratio and share the challenges of conventional low-dose computed tomography such as ring artifacts. Ring artifacts arise from errors in the flat fields and can significantly degrade the quality of the reconstruction. We propose an extended flat-field model that exploits high correlation in the spectral flat fields to reduce ring artifacts in channel-wise reconstructions. The extended model relies on the assumption that the spectral flat fields can be well-approximated by a low-rank matrix. Our proposed model works directly on the spectral flat fields and can be combined with any existing reconstruction model, e.g. filtered back projection and iterative methods. The proposed model is validated on a neutron data set. The results show that our method successfully diminishes ring artifacts and improves the quality of the reconstructions. Moreover, the results indicate that our method is robust; it only needs a single spectral flat-field image, whereas existing methods need multiple spectral flat-field images to reach a similar level of ring reduction.
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Mar 2023
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I14-Hard X-ray Nanoprobe
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Diamond Proposal Number(s):
[28142]
Open Access
Abstract: The interaction of a focused X-ray beam with a sample in a scanning probe experiment can provide a variety of information about the interaction volume. In many scanning probe experiments X-ray fluorescence (XRF) is supplemented with measurements of the transmitted or scattered intensity using a pixelated detector. The automated extraction of different signals from an area pixelated detector is described, in particular the methodology for extracting differential phase contrast (DPC) is demonstrated and different processing methods are compared across a range of samples. The phase shift of the transmitted X-ray beam by the sample, extracted from DPC, is also compared with ptychography measurements to provide a qualitative and quantitative comparison. While ptychography produces a superior image, DPC can offer a simple, flexible method for phase contrast imaging which can provide fast results and feedback during an experiment; furthermore, for many science problems, such as registration of XRF in a lighter matrix, DPC can provide sufficient information to meet the experimental aims. As the DPC technique is a quantitative measurement, it can be expanded to spectroscopic studies and a demonstration of DPC for spectro-microscopy measurements is presented. Where ptychography can separate the absorption and phase shifts by the sample, quantitative interpretation of a DPC image or spectro-microscopy signal can only be performed directly when absorption is negligible or where the absorption contribution is known and the contributions can be fitted.
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Dec 2022
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I14-Hard X-ray Nanoprobe
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Diamond Proposal Number(s):
[31039]
Open Access
Abstract: Combinations of spectroscopic analysis and microscopic techniques are used across many disciplines of scientific research, including material science, chemistry and biology. X-ray spectromicroscopy, in particular, is a powerful tool used for studying chemical state distributions at the micro and nano scales. With the beam fixed, a specimen is typically rastered through the probe with continuous motion and a range of multimodal data is collected at fixed time intervals. The application of this technique is limited in some areas due to: long scanning times to collect the data, either because of the area/volume under study or the compositional properties of the specimen; and material degradation due to the dose absorbed during the measurement. In this work, we propose a novel approach for reducing the dose and scanning times by undersampling the raster data. This is achieved by skipping rows within scans and reconstructing the x-ray spectromicroscopic measurements using low-rank matrix completion. The new method is robust and allows for 5 to 6-fold reduction in sampling. Experimental results obtained on real data are illustrated.
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Nov 2022
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B16-Test Beamline
Metrology
Optics
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Open Access
Abstract: Speckle-based at-wavelength metrology techniques now play an important role in X-ray wavefront measurements. However, for reflective X-ray optics, the majority of existing speckle-based methods fail to provide reliable 2D information about the optical surface being characterized. Compared with the 1D information typically output from speckled-based methods, a 2D map is more informative for understanding the overall quality of the optic being tested. In this paper, we propose a method for in situ 2D absolute metrology of weakly focusing X-ray mirrors. Importantly, the angular misalignment of the mirror can be easily corrected with the proposed 2D processing procedure. We hope the speckle pattern data processing method presented here will help to extend this technique to wider applications in the synchrotron radiation and X-ray free-electron laser communities.
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Nov 2022
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Nanna
Zhou Hagström
,
Michael
Schneider
,
Nico
Kerber
,
Alexander
Yaroslavtsev
,
Erick
Burgos Parra
,
Marijan
Beg
,
Martin
Lang
,
Christian M.
Günther
,
Boris
Seng
,
Fabian
Kammerbauer
,
Horia
Popescu
,
Matteo
Pancaldi
,
Kumar
Neeraj
,
Debanjan
Polley
,
Rahul
Jangid
,
Stjepan B.
Hrkac
,
Sheena K. K.
Patel
,
Sergei
Ovcharenko
,
Diego
Turenne
,
Dmitriy
Ksenzov
,
Christine
Boeglin
,
Marina
Baidakova
,
Clemens
Von Korff Schmising
,
Martin
Borchert
,
Boris
Vodungbo
,
Kai
Chen
,
Chen
Luo
,
Florin
Radu
,
Leonard
Müller
,
Miriam
Martínez Flórez
,
André
Philippi-Kobs
,
Matthias
Riepp
,
Wojciech
Roseker
,
Gerhard
Grübel
,
Robert
Carley
,
Justine
Schlappa
,
Benjamin E.
Van Kuiken
,
Rafael
Gort
,
Laurent
Mercadier
,
Naman
Agarwal
,
Loïc
Le Guyader
,
Giuseppe
Mercurio
,
Martin
Teichmann
,
Jan Torben
Delitz
,
Alexander
Reich
,
Carsten
Broers
,
David
Hickin
,
Carsten
Deiter
,
James
Moore
,
Dimitrios
Rompotis
,
Jinxiong
Wang
,
Daniel
Kane
,
Sandhya
Venkatesan
,
Joachim
Meier
,
Florent
Pallas
,
Tomasz
Jezynski
,
Maximilian
Lederer
,
Djelloul
Boukhelef
,
Janusz
Szuba
,
Krzysztof
Wrona
,
Steffen
Hauf
,
Jun
Zhu
,
Martin
Bergemann
,
Ebad
Kamil
,
Thomas
Kluyver
,
Robert
Rosca
,
Michał
Spirzewski
,
Markus
Kuster
,
Monica
Turcato
,
David
Lomidze
,
Andrey
Samartsev
,
Jan
Engelke
,
Matteo
Porro
,
Stefano
Maffessanti
,
Karsten
Hansen
,
Florian
Erdinger
,
Peter
Fischer
,
Carlo
Fiorini
,
Andrea
Castoldi
,
Massimo
Manghisoni
,
Cornelia Beatrix
Wunderer
,
Eric E.
Fullerton
,
Oleg G.
Shpyrko
,
Christian
Gutt
,
Cecilia
Sanchez-Hanke
,
Hermann A.
Dürr
,
Ezio
Iacocca
,
Hans T.
Nembach
,
Mark W.
Keller
,
Justin M.
Shaw
,
Thomas J.
Silva
,
Roopali
Kukreja
,
Hans
Fangohr
,
Stefan
Eisebitt
,
Mathias
Kläui
,
Nicolas
Jaouen
,
Andreas
Scherz
,
Stefano
Bonetti
,
Emmanuelle
Jal
Open Access
Abstract: The advent of X-ray free-electron lasers (XFELs) has revolutionized fundamental science, from atomic to condensed matter physics, from chemistry to biology, giving researchers access to X-rays with unprecedented brightness, coherence and pulse duration. All XFEL facilities built until recently provided X-ray pulses at a relatively low repetition rate, with limited data statistics. Here, results from the first megahertz-repetition-rate X-ray scattering experiments at the Spectroscopy and Coherent Scattering (SCS) instrument of the European XFEL are presented. The experimental capabilities that the SCS instrument offers, resulting from the operation at megahertz repetition rates and the availability of the novel DSSC 2D imaging detector, are illustrated. Time-resolved magnetic X-ray scattering and holographic imaging experiments in solid state samples were chosen as representative, providing an ideal test-bed for operation at megahertz rates. Our results are relevant and applicable to any other non-destructive XFEL experiments in the soft X-ray range.
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Nov 2022
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B16-Test Beamline
I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[27987, 20763, 27144, 31131]
Abstract: X-ray phase-contrast tomography (X-PCT) techniques are capable of imaging samples with small differences in densities. They enable scientists to study biological or medical samples using high energy X-rays, which means less X-ray absorption and less sample damage, with high contrast quality. One branch of these techniques known as speckle-based methods have been well developed and demonstrated on real applications by different groups of developers using their own codes. However, there is lack of collective effort to package these methods into an open-source software which is easy-to-install, easy-to-use, well-documented, and optimized for speed. Such software is crucial to make the X-PCT techniques accessible to generic users and become regular tools. This report demonstrates the effort which implements speckle-based phase-retrieval methods in Python and GPU.
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Oct 2022
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Abstract: Synchrotron radiation based techniques provide unique insight into both the element and time resolved magnetization behaviour in magnetic spin systems. X-ray detected ferromagnetic resonance (XFMR) has recently emerged as a powerful synchrotron-radiation-based tool able to study the element- selective magnetization dynamics [1]. Magnetic and chemical contrast in XFMR is obtained by x-ray magnetic circular dichroism (XMCD), while the phase difference between the magnetization precessions is monitored using stroboscopic probing. A unique property of time-resolved XFMR is the visualization of the magnetization precession for each individual layer in a magnetic device. Measurement of the amplitude and phase response of the magnetic layers gives a clear signature of spin-transfer torque (STT) coupling between ferromagnetic layers due to spin pumping. We highlight the power of two recent developments, utilizing x-ray scattering techniques to reveal the precessional magnetization dynamics of ordered spin structures in the GHz regime, both in diffraction and reflection configurations. Our recently developed diffraction and reflectometry ferromagnetic resonance (DFMR and RFMR) techniques provide novel ways to explore the dynamics of modern
magnetic materials, thereby opening up new pathways for the development of spintronic devices [2-5]. We provide an overview of these techniques and discuss the new understanding they provide into the magnetization dynamics in the chiral magnetic structure in Y-type hexaferrite and the depth dependence to the magnetization dynamics in a [CoFeB/MgO/Ta]4 multilayer. Our characterization tools for the exploration of the dynamics of chiral and multilayered magnetic materials are significant to the development of high-density and low-energy consumption data processing solutions.
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Aug 2022
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I13-1-Coherence
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Abstract: In this work, a characterization and optimization of phase-sensitive X-ray imaging techniques with a focus
on the field of laboratory astrophysics is given. Here, the advent of hard X-ray free electron lasers offers
novel opportunities as single-pulse imaging with sub-picosecond temporal resolution becomes possible. The
use of phase-sensitive techniques is often mandatory as micro- and nanoscopic samples show little or no attenuation
contrast. In order to fully benefit from the short pulse lengths at X-ray free electron lasers, these
methods should be reconcilable with single-exposure acquisition schemes. This task is complicated by zeroes
in the respective transfer functions of the imaging systems. Therefore, direct inversions are typically not
possible and sophisticated algorithms are required for the image reconstruction. Overall, this thesis mainly
focuses upon the grating-based X-ray imaging technique, also known as Talbot interferometry. For comparison,
propagation-based phase contrast imaging will also be considered. The investigations are divided into
analytical considerations, numerical simulations, and experimental implementations of the respective imaging
techniques.
An analytical examination of the image formation within a Talbot interferometer is presented. This process
can become complicated, especially for applications in X-ray microscopes. Here, transverse shifts of the
interference pattern in general depend nonlinearly on the phase differences across the X-ray wave field. Existing
reconstruction methods on the basis of deconvolutions then rely on idealized conditions, thus limiting
the experimental applicability of the method. In addition, the achievable spatial resolution of Talbot interferometry
in single-exposure applications is typically limited to the demagnified fringe period of the interference
pattern.
In order to resolve the limitations regarding the applicability, three novel reconstruction methods for Talbot
interferometry are conceptualized and implemented: the design of a beam-splitting diffraction grating featuring
only two diffraction orders, a two-stage deconvolution approach, and a statistical image reconstruction
method based on an analytical forward model of the imaging process and a regularized maximum likelihood
approach. The three schemes are validated on the basis of simulated data. They all prove advantageous when
the premises for standard deconvolution-based reconstructions are not met. The statistical image reconstruction
technique seems most promising as it achieves the best reconstruction quality at low photon numbers and
also circumvents the abovementioned limitations regarding the spatial resolution.
Building up on the simulative studies, two experimental realizations of Talbot interferometry at synchrotron
light sources are presented. In the first experiment, the single-exposure phase imaging capabilities
of Talbot interferometry in conjunction with the statistical image reconstruction method are investigated and
characterized on the basis of simple test samples. The broadened experimental applicability is demonstrated
through the retrieval of Fresnel diffraction images in an X-ray projection microscope. While a comparative
implementation of propagation-based phase contrast imaging at the same instrument still yields a superior
spatial resolution, the mitigation of limitations due to the fringe period is also verified experimentally. In the
second experiment, single-exposure phase imaging with both the grating-based and the propagation-based
approach is employed in order to monitor the moistening process of wood on the level of single wood cells...
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Aug 2022
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B22-Multimode InfraRed imaging And Microspectroscopy
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Open Access
Abstract: We present an in-vacuum mechanical chopper running at high speed and integrated into a magnetic levitating motor for modulating optical beams up to 200 kHz. The compact chopper rotor allows fast acceleration (10 kHz s−1 as standard) for rapid tuning of the modulation frequency, while 1 mm diameter slots provide high optical throughput for larger infrared beams. The modulation performances are assessed using a reference visible laser and the high brightness, broadband, infrared (IR) beam of synchrotron radiation at the MIRIAM beamline B22 at Diamond Light Source, UK. For our application of IR nanospectroscopy, minimizing the temporal jitter on the modulated beam due to chopper manufacturing and control tolerances is essential to limit the noise level in measurements via lock-in detection, while high modulation frequencies are needed to achieve high spatial resolution in photothermal nanospectroscopy. When reaching the maximum chopping frequency of 200 kHz, the jitter was found to be 0.9% peak-to-peak. The described chopper now replaces the standard ball-bearing chopper in our synchrotron-based FTIR photothermal nanospectroscopy system, and we demonstrate improved spectroscopy results on a 200 nm thickness polymer film.
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Aug 2022
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B16-Test Beamline
Optics
|
Open Access
Abstract: Advances in accelerator technologies have enabled the continuous development of synchrotron radiation and X-ray free electron laser (XFEL) sources. At the same time, it has been critical to perform in-situ wavefront sensing to aid delivery of high-quality X-ray beams to the end users of these facilities. The speckle-based scanning technique has obtained popularity due to its high spatial resolution and superior sensitivity compared to other wavefront sensing methods. However, these advantages often come at the expense of longer data acquisition times since multiple images have to be collected to derive the necessary wavefront information. Whereas initial speckle tracking techniques could obtain wavefront information relatively quickly, the installation of additional hardware was routinely required to do so. Here, we propose a novel speckle-based approach, termed Alternating Speckle Tracking (AST), to perform fast wavefront sensing within a conventional beamline setup. The wavefront information derived from the new technique has proven to be valuable for many applications that require temporal resolution. Importantly, both horizontal and vertical wavefront information can be simultaneously derived by moving the speckle generator along the diagonal direction. We expect this method will be widely used by the synchrotron radiation and XFEL community in the future.
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Aug 2022
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