66 research outputs found
Bent crystal spectrometer for both frequency and wavenumber resolved x-ray scattering at a seeded free-electron laser
We present a cylindrically curved GaAs x-ray spectrometer with energy
resolution and wave-number resolution of
, allowing plasmon scattering at the resolution
limits of the Linac Coherent Light Source (LCLS) x-ray free-electron laser. It
spans scattering wavenumbers of 3.6 to \AA\ in 100 separate bins, with
only 0.34\% wavenumber blurring. The dispersion of 0.418~eV/m agrees
with predictions within 1.3\%. The reflection homogeneity over the entire
wavenumber range was measured and used to normalize the amplitude of scattering
spectra. The proposed spectrometer is superior to a mosaic HAPG spectrometer
when the energy resolution needs to be comparable to the LCLS seeded bandwidth
of 1~eV and a significant range of wavenumbers must be covered in one exposure
The Phase-Contrast Imaging Instrument at the Matter in Extreme Conditions Endstation at LCLS
We describe the Phase-Contrast Imaging instrument at the Matter in Extreme
Conditions (MEC) endstation of the Linac Coherent Light Source. The instrument
can image phenomena with a spatial resolution of a few hundreds of nanometers
and at the same time reveal the atomic structure through X-ray diffraction,
with a temporal resolution better than 100 femtosecond. It was specifically
designed for studies relevant to High-Energy-Density Science and can monitor,
e.g., shock fronts, phase transitions, or void collapses. This versatile
instrument was commissioned last year and is now available to the MEC user
community
Stochastic polarization switching dynamics in Vertical-Cavity Surface Emitting Lasers: Theory and Experiment
7 pages, 5 figures.We present an analytical, numerical and experimental study of the switching time and
jitter of current induced polarization switching in Vertical-Cavity Surface-Emitting Lasers in the presence of spontaneous emission noise. Assuming that the switching is induced by changes in the dichroism, the problem can be reduced to the well-known first passage time problem in gain switched Class-A lasers. The theoretical results obtained in this way show excellent agreement both with numerical simulations based on the full rate equations model, and with experiments performed on oxide-confined Vertical-Cavity Surface-Emitting Lasers.This work was supported in part by the Belgian government under the Interuniversity Attraction
Pole program (IAP V/18), in part by the Concerted Research Action, and in part by the Research Council of the Vrije Universiteit Brussel. The collaboration between the groups in Brussels, Palma de Mallorca, Ulm, and Florence
was made possible through the European RTN network VISTA under Contract HPRN-CT-2000-00034. Additional support from, and discussions within, the framework of the European COST actions 268 and 288 are acknowledged. The work of J. Danckaert, G. Verschaffelt, and B. Nagler was supported by the Fund for Scientific Research—Flanders.Peer reviewe
Measurement of competing pathways in a shock-induced phase transition in zirconium by femtosecond diffraction
The traditional picture of solid-solid phase transformations assumes an
ordered parent phase transforms into an ordered daughter phase via a single
unique pathway. Zirconium and its prototypical phase transition from hexagonal
close-packed (hcp) to simple hexagonal (hex-3) structure has generated
considerable controversy over several decades regarding which mechanism
mediates the transformation. However, a lack of in situ measurements over the
relevant atomistic timescales has hindered our ability to identify the true
pathway. In this study, we exploit femtosecond X-ray diffraction coupled with
nanosecond laser compression to give unprecedented insights into the
complexities of how materials transform at the lattice level. We observe
single-crystal zirconium changing from hcp to a hex-3 structure via not one but
three competing pathways simultaneously. Concurrently, we also observe a broad
diffuse background underlying the sharp Bragg diffraction during the
transition. We corroborate our observation of the diffuse signal with
multimillion-atom molecular dynamics simulations using a machine-learned
interatomic potential. Our study demonstrates that the traditional mechanistic
view of transitions may fail for even an elemental metal and that the
mechanisms by which materials transform are far more intricate than generally
thought
Polarization-mode hopping in single-mode vertical-cavity surface-emitting lasers: Theory and experiment.
In this paper, we present a theoretical and experimental analysis of stochastic effects observed in polarization switching vertical-cavity surface-emitting lasers. We make a thorough comparison between theoretical predictions and experiments, comparing measured quasipotentials and dwell times. The correspondence between our theoretical model based on stochastic intensity rate equations and the experiments is found to be very good
Femtosecond X-Ray Diffraction Studies of the Reversal of the Microstructural Effects of Plastic Deformation during Shock Release of Tantalum
We have used femtosecond x-ray diffraction (XRD) to study laser-shocked fiber-textured polycrystalline tantalum targets as the 37-253 GPa shock waves break out from the free surface. We extract the time and depth-dependent strain profiles within the Ta target as the rarefaction wave travels back into the bulk of the sample. In agreement with molecular dynamics (MD) simulations the lattice rotation and the twins that are formed under shock-compression are observed to be almost fully eliminated by the rarefaction process
Imaging Shock Waves in Diamond with Both High Temporal and Spatial Resolution at an XFEL
The advent of hard x-ray free-electron lasers (XFELs) has opened up a variety of scientific opportunities in areas as diverse as atomic physics, plasma physics, nonlinear optics in the x-ray range and protein crystallography. In this article, we access a new field of science by measuring quantitatively the local bulk properties and dynamics of matter under extreme conditions, in this case by using the short XFEL pulse to image an elastic compression wave in diamond. The elastic wave was initiated by an intense optical laser pulse and was imaged at different delay times after the optical pump pulse using magnified x-ray phase-contrast imaging. The temporal evolution of the shock wave can be monitored, yielding detailed information on shock dynamics, such as the shock velocity, the shock front width and the local compression of the material. The method provides a quantitative perspective on the state of matter in extreme conditions
Investigating mechanisms of state localization in highly ionized dense plasmas
Producción CientÃficaWe present experimental observations of Kβ emission from highly charged Mg ions at solid density, driven by intense x rays from a free electron laser. The presence of Kβ emission indicates the n=3 atomic shell is relocalized for high charge states, providing an upper constraint on the depression of the ionization potential. We explore the process of state relocalization in dense plasmas from first principles using finite-temperature density functional theory alongside a wave-function localization metric, and find excellent agreement with experimental results.This work has been supported by the Spanish Ministry of Science and Innovation under Research Grant No. PID2019-108764RB-I0
Investigating Mechanisms of State Localization in Highly-Ionized Dense Plasmas
We present the first experimental observation of K emission from
highly charged Mg ions at solid density, driven by intense x-rays from a free
electron laser. The presence of K emission indicates the atomic
shell is relocalized for high charge states, providing an upper constraint on
the depression of the ionization potential. We explore the process of state
relocalization in dense plasmas from first principles using finite-temperature
density functional theory alongside a wavefunction localization metric, and
find excellent agreement with experimental results.Comment: 22 pages, 13 figure
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