[show abstract][hide abstract] ABSTRACT: Single shot diffraction imaging experiments via X-ray free-electron lasers can generate as many as hundreds of thousands of diffraction patterns of scattering objects. Recovering the real space contrast of a scattering object from these patterns currently requires a reconstruction process with user guidance in a number of steps, introducing severe bottlenecks in data processing. We present a series of measures that replace user guidance with algorithms that reconstruct contrasts in an unsupervised fashion. We demonstrate the feasibility of automating the reconstruction process by generating hundreds of contrasts obtained from soot particle diffraction experiments.
[show abstract][hide abstract] ABSTRACT: We report on strain analysis by nano-beam electron diffraction with a
spatial resolution of 0.5nm and a strain precision in the
4-7·10-4 range. Series of up to 160000
CBED patterns have been acquired in STEM mode with a semi-convergence
angle of the incident probe of 2.6mrad, which enhances the spatial
resolution by a factor of 5 compared to nearly parallel illumination.
Firstly, we summarise 3 different algorithms to detect CBED disc
positions accurately: selective edge detection and circle fitting,
radial gradient maximisation and cross-correlation with masks. They
yield equivalent strain profiles in growth direction for a stack of 5
layers with tensile and compressive strain. Secondly, we use a direct
electron read-out pnCCD detector with ultrafast readout hardware and a
quantum efficiency close to 1 both to show that the same strain profiles
are obtained at 200 times higher readout rates of 1kHz and to enhance
strain precision to 3.5·10-4 by recording the
weak 008 disc.
Journal of Physics Conference Series 11/2013; 471(1):2024-.
[show abstract][hide abstract] ABSTRACT: We report experimental results on x-ray diffraction of quantum-state-selected
and strongly aligned ensembles of the prototypical asymmetric rotor molecule
2,5-diiodobenzonitrile using the Linac Coherent Light Source. The experiments
demonstrate pioneering steps toward a new bottom-up approach to diffractive
imaging of distinct structures of individual, isolated gas-phase molecules. We
confirm several key ingredients of single molecule diffraction experiments: the
abilities to detect and count individual scattered x-ray photons in single shot
diffraction data, to deliver state-selected, e.g., structural-isomer-selected,
ensembles of molecules to the x-ray interaction volume, and to strongly align
the scattering molecules. Our approach, using ultrashort x-ray pulses, is
suitable to study ultrafast dynamics of isolated molecules.
[show abstract][hide abstract] ABSTRACT: This White Paper, submitted to the recent ESA call for science themes to
define its future large missions, advocates the need for a transformational
leap in our understanding of two key questions in astrophysics: 1) How does
ordinary matter assemble into the large scale structures that we see today? 2)
How do black holes grow and shape the Universe? Hot gas in clusters, groups and
the intergalactic medium dominates the baryonic content of the local Universe.
To understand the astrophysical processes responsible for the formation and
assembly of these large structures, it is necessary to measure their physical
properties and evolution. This requires spatially resolved X-ray spectroscopy
with a factor 10 increase in both telescope throughput and spatial resolving
power compared to currently planned facilities. Feedback from supermassive
black holes is an essential ingredient in this process and in most galaxy
evolution models, but it is not well understood. X-ray observations can
uniquely reveal the mechanisms launching winds close to black holes and
determine the coupling of the energy and matter flows on larger scales. Due to
the effects of feedback, a complete understanding of galaxy evolution requires
knowledge of the obscured growth of supermassive black holes through cosmic
time, out to the redshifts where the first galaxies form. X-ray emission is the
most reliable way to reveal accreting black holes, but deep survey speed must
improve by a factor ~100 over current facilities to perform a full census into
the early Universe. The Advanced Telescope for High Energy Astrophysics
(Athena+) mission provides the necessary performance (e.g. angular resolution,
spectral resolution, survey grasp) to address these questions and revolutionize
our understanding of the Hot and Energetic Universe. These capabilities will
also provide a powerful observatory to be used in all areas of astrophysics.
[show abstract][hide abstract] ABSTRACT: Characterizing intense, focused x-ray free electron laser (FEL) pulses is crucial for their use in diffractive imaging. We describe how the distribution of average phase tilts and intensities on hard x-ray pulses with peak intensities of 10<sup>21</sup> W/m<sup>2</sup> can be retrieved from an ensemble of diffraction patterns produced by 70 nm-radius polystyrene spheres, in a manner that mimics wavefront sensors. Besides showing that an adaptive geometric correction may be necessary for diffraction data from randomly injected sample sources, our paper demonstrates the possibility of collecting statistics on structured pulses using only the diffraction patterns they generate and highlights the imperative to study its impact on single-particle diffractive imaging.
[show abstract][hide abstract] ABSTRACT: A new approach to achieve sub-pixel spatial resolution in a pnCCD
detector with 75 × 75 μm2 pixel size is proposed for
X-ray applications in single photon counting mode. The approach
considers the energy dependence of the charge cloud created by a single
photon and its split probabilities between neighboring pixels of the
detector based on a rectangular model for the charge cloud density. For
cases where the charge of this cloud becomes distributed over three or
four pixels the center position of photon impact can be reconstructed
with a precision better than 2 μm. The predicted charge cloud sizes
are tested at selected X-ray fluorescence lines emitting energies
between 6.4 keV and 17.4 keV and forming charge clouds with size (rms)
varying between 8 μm and 10 μm respectively. The 2 μm enhanced
spatial resolution of the pnCCD is verified by means of an x-ray
transmission experiment throughout an optical grating.
Journal of Instrumentation 05/2013; 8(05):P05005. · 1.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: X-ray free-electron lasers (FELs) enable crystallographic data collection using extremely bright femtosecond pulses from microscopic crystals beyond the limitations of conventional radiation damage. This diffraction-before-destruction approach requires a new crystal for each FEL shot and, since the crystals cannot be rotated during the X-ray pulse, data collection requires averaging over many different crystals and a Monte Carlo integration of the diffraction intensities, making the accurate determination of structure factors challenging. To investigate whether sufficient accuracy can be attained for the measurement of anomalous signal, a large data set was collected from lysozyme microcrystals at the newly established `multi-purpose spectroscopy/imaging instrument' of the SPring-8 Ångstrom Compact Free-Electron Laser (SACLA) at RIKEN Harima. Anomalous difference density maps calculated from these data demonstrate that serial femtosecond crystallography using a free-electron laser is sufficiently accurate to measure even the very weak anomalous signal of naturally occurring S atoms in a protein at a photon energy of 7.3 keV.
[show abstract][hide abstract] ABSTRACT: In this work we study the response of a pnCCD by means of X-ray spectroscopy in the energy range between 6 keV and 20 keV and by Laue diffraction techniques. The analyses include measurements of characteristic detector parameters like energy resolution, count rate capability and effects of different gain settings. The limit of a single photon counting operation in white beam X-ray diffraction experiments is discussed with regard to the occurrence of pile-up events, for which the energy information about individual photons is lost. In case of monochromatic illumination the pnCCD can be used as a fast conventional CCD with a charge handling capacity (CHC) of about 300,000 electrons per pixel. If the CHC is exceeded, any surplus charge will spill to neighboring pixels perpendicular to the transfer direction due to electrostatic repulsion. The possibilities of increasing the number of storable electrons are investigated for different voltage settings by exposing a single pixel with X-rays generated by a microfocus X-ray source. The pixel binning mode is tested as an alternative approach that enables a pnCCD operation with significantly shorter readout times.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 05/2013; 711:132–142. · 1.14 Impact Factor
[show abstract][hide abstract] ABSTRACT: Ultrafast laser techniques have revealed extraordinary spin dynamics in magnetic materials that equilibrium descriptions of magnetism cannot explain. Particularly important for future applications is understanding non-equilibrium spin dynamics following laser excitation on the nanoscale, yet the limited spatial resolution of optical laser techniques has impeded such nanoscale studies. Here we present ultrafast diffraction experiments with an X-ray laser that probes the nanoscale spin dynamics following optical laser excitation in the ferrimagnetic alloy GdFeCo, which exhibits macroscopic all-optical switching. Our study reveals that GdFeCo displays nanoscale chemical and magnetic inhomogeneities that affect the spin dynamics. In particular, we observe Gd spin reversal in Gd-rich nanoregions within the first picosecond driven by the non-local transfer of angular momentum from larger adjacent Fe-rich nanoregions. These results suggest that a magnetic material's microstructure can be engineered to control transient laser-excited spins, potentially allowing faster (~ 1 ps) spin reversal than in present technologies.
[show abstract][hide abstract] ABSTRACT: Unraveling the complex morphology of functional materials like core–shell nanoparticles and its evolution in different environments is still a challenge. Only recently has the single-particle coherent diffraction imaging (CDI), enabled by the ultrabright femtosecond free-electron laser pulses, provided breakthroughs in understanding mesoscopic morphology of nanoparticulate matter. Here, we report the first CDI results for Co@SiO 2 core–shell nanoparticles randomly clustered in large airborne aggregates, obtained using the x-ray free-electron laser at the Linac Coherent Light Source. Our experimental results compare favourably with simulated diffraction patterns for clustered Co@SiO 2 nanoparticles with ∼10 nm core diameter and ∼30 nm shell outer diameter, which confirms the ability to resolve the mesoscale morphology of complex metastable structures. The findings in this first morphological study of core–shell nanomaterials are a solid base for future time-resolved studies of dynamic phenomena in complex nanoparticulate matter using x-ray lasers.
Journal of Physics B Atomic Molecular and Optical Physics 01/2013; 46(16):164033. · 2.03 Impact Factor
[show abstract][hide abstract] ABSTRACT: Diffractive imaging with free-electron lasers allows structure determination from ensembles of weakly scattering identical nanoparticles. The ultra-short, ultra-bright X-ray pulses provide snapshots of the randomly oriented particles frozen in time, and terminate before the onset of structural damage. As signal strength diminishes for small particles, the synthesis of a three-dimensional diffraction volume requires simultaneous involvement of all data. Here we report the first application of a three-dimensional spatial frequency correlation analysis to carry out this synthesis from noisy single-particle femtosecond X-ray diffraction patterns of nearly identical samples in random and unknown orientations, collected at the Linac Coherent Light Source. Our demonstration uses unsupported test particles created via aerosol self-assembly, and composed of two polystyrene spheres of equal diameter. The correlation analysis avoids the need for orientation determination entirely. This method may be applied to the structural determination of biological macromolecules in solution.
[show abstract][hide abstract] ABSTRACT: X-ray free-electron lasers provide unique opportunities for exploring ultrafast dynamics and for imaging the structures of complex systems. Understanding the response of individual atoms to intense X-rays is essential for most free-electron laser applications. First experiments have shown that, for light atoms, the dominant interaction mechanism is ionization by sequential electron ejection, where the highest charge state produced is defined by the last ionic state that can be ionized with one photon. Here, we report an unprecedentedly high degree of ionization of xenon atoms by 1.5 keV free-electron laser pulses to charge states with ionization energies far exceeding the photon energy. Comparing ion charge-state distributions and fluorescence spectra with state-of-the-art calculations, we find that these surprisingly high charge states are created via excitation of transient resonances in highly charged ions, and predict resonance enhanced absorption to be a general phenomenon in the interaction of intense X-rays with systems containing high-Z constituents.
[show abstract][hide abstract] ABSTRACT: A high-speed direct electron detection system is introduced to the field of transmission electron microscopy and applied to strain measurements in semiconductor nanostructures. In particular, a focused electron probe with a diameter of 0.5 nm was scanned over a fourfold quantum layer stack with alternating compressive and tensile strain and diffracted discs have been recorded on a scintillator-free direct electron detector with a frame time of 1 ms. We show that the applied algorithms can accurately detect Bragg beam positions despite a significant point spread each 300 kV electron causes during detection on the scintillator-free camera. For millisecond exposures, we find that strain can be measured with a precision of 1.3 × 10−3, enabling, e.g., strain mapping in a 100×100 nm2 region with 0.5 nm resolution in 40 s.
[show abstract][hide abstract] ABSTRACT: With the first X-ray free-electron laser (FEL), the Linac Coherent Light
Source (LCLS), multiphoton ionization has been pushed to a new regime,
where atoms and molecules are not just ionized by a series of valence
ionizations but "from the inside out". At unprecedented high intensities
and short pulse durations in the soft X-ray regime, a series of
inner-shell photoionizations followed by cascades of Auger decays was
observed to lead to highly charged final states in rare gases such as
Ne, Ar, Kr, and Xe. Ion time-of-flight and fluorescence spectra were
recorded for different FEL pulse energies and pulse lengths and compared
to theoretical models to explain the underlying processes that lead to
unexpectedly high charge states in Xe.
Journal of Physics Conference Series 11/2012; 388(2):2022-.
[show abstract][hide abstract] ABSTRACT: This is the manuscript submitted to the publisher, NOT the final i.e. published version!
The Max Planck Advanced Study Group (ASG) at the Center for Free Electron Laser Science (CFEL) has created the CFEL ASG Software Suite CASS to view, process and analyse multi-parameter experimental data acquired at Free Electron Lasers (FELs) using the CFEL ASG Multi Purpose (CAMP) instrument .
The software is based on a modular design so that it can be adjusted to accommodate the needs of all the various experiments that are conducted with the CAMP instrument. One of the key aspects of CASS is that it can be used either ‘on-line’, using a live data stream from the free-electron laser facility’s data acquisition system to guide the experiment, and ‘off-line’, on data acquired from a previous experiment which has been saved to file.
[show abstract][hide abstract] ABSTRACT: We report on our activities, currently in progress, aimed at performing
accelerator experiments with soft protons and hyper-velocity dust particles.
They include tests of different types of X-ray detectors and related components
(such as filters) and measurements of scattering of soft protons and
hyper-velocity dust particles off X-ray mirror shells. These activities have
been identified as a goal in the context of a number of ongoing space projects
in order to assess the risk posed by environmental radiation and dust and
qualify the adopted instrumentation with respect to possible damage or
performance degradation. In this paper we focus on tests for the Silicon Drift
Detectors (SDDs) used aboard the LOFT space mission. We use the Van de Graaff
accelerators at the University of T\"ubingen and at the Max Planck Institute
for Nuclear Physics (MPIK) in Heidelberg, for soft proton and hyper-velocity
dust tests respectively. We present the experimental set-up adopted to perform
the tests, status of the activities and some very preliminary results achieved
at present time.
[show abstract][hide abstract] ABSTRACT: Athena is an X-ray observatory-class mission concept, developed from April to
December 2011 as a result of the reformulation exercise for L-class mission
proposals in the framework of ESA's Cosmic Vision 2015-2025. Athena's science
case is that of the Universe of extremes, from Black Holes to Large-scale
structure. The specific science goals are structured around three main pillars:
"Black Holes and accretion physics", "Cosmic feedback" and "Large-scale
structure of the Universe". Underpinning these pillars, the study of hot
astrophysical plasmas offered by Athena broadens its scope to virtually all
corners of Astronomy. The Athena concept consists of two co-aligned X-ray
telescopes, with focal length 12 m, angular resolution of 10" or better, and
totalling an effective area of 1 m2 at 1 keV (0.5 m2 at 6 keV). At the focus of
one of the telescopes there is a Wide Field Imager (WFI) providing a field of
view of 24'\times 24', 150 eV spectral resolution at 6 keV, and high count rate
capability. At the focus of the other telescope there is the X-ray
Microcalorimeter Spectrometer (XMS), a cryogenic instrument offering a spectral
resolution of 3 eV over a field of view of 2.3' \times 2.3'. Although Athena
has not been selected as ESA's Cosmic Vision 2015-2025 L1 mission, its science
goals and concept conform the basis of what should become ESA's X-ray astronomy
[show abstract][hide abstract] ABSTRACT: The Mercury Imaging X-ray Spectrometer (MIXS) is an instrument on board
of the 5th ESA cornerstone mission BepiColombo. This Spectrometer
comprises two instruments for imaging x-ray spectroscopy of the Mercury
surface. The detector plane arrays (DPA) for the energy and spatial
resolved detection of x-rays are based on DEPFET (Depleted P-channel
FET) macropixel detectors with 64×64 pixel each and 300×300
μm2 pixel size. The MIXS target energy band is from 0.5 to
7 keV with an energy resolution better than 200 eV at 1 keV at mission
end. This allows to access the Fe-L line at about 0.7 keV, which was not
accessible to previous instruments, and to separate the x-ray lines of
the elements of interest. Before a detector chip is integrated into a
detector module, it is electrically pre-characterized in order to select
only the best chips for the complex and time-consuming integration. The
high degree of complexity of the integration process comes from the need
to thermally decouple the detector chip from its readout and steering
ASICs by a sophisticated mechanical structure, due to the limited amount
of cooling power available for the instrument. After the spectroscopic
characterization of the detector modules, the flight and flight spare
detectors were calibrated at the PTB (Physikalisch-Technische
Bundesanstalt) beamlines at the BESSY-II synchrotron. We report on the
pre-characterization, integration, qualification and calibration of MIXS
flight and flight spare detectors, which is now successfully completed.