Search

Shock experiments give a unique insight into the behavior of matter subjected to extremely high pressures and temperatures. Understanding the behavior of materials under such extreme conditions is key to modeling material failure and deformation dynamics under impact. While studies on pure silica are extensive, the shock behavior of other commercial silicates that contain additional oxides has not been systematically investigated. To better understand the role of composition in the dynamic behavior of silicates, we performed laser-driven dynamic compression experiments on soda-lime glass (SLG) up to 315 GPa. Using the accurate pulse shaping offered by the long pulse laser system at the Matter in Extreme Conditions end-station at the Linac Coherent Light Source, SLG was shock compressed along the Hugoniot to multiple pressure-temperature points. Velocity Interferometer System for Any Reflector was used to measure the velocity and determine the pressure inside the SLG. The Us–up relationship obtained agrees well with the previous parallel plate impact studies. Within the error bars, no transformation to the crystalline phase was observed up to 70 GPa, which is in contrast to the behavior of pure silica under shock compression. Our studies show that the glass composition strongly influences the shock compression behavior of the silicate glasses.

Since October 2020, the first digital health applications (DiGA) have been listed with the Federal Institute for Drugs and Medical Devices (BfArM) and can be prescribed by physicians and psychotherapists in the statutory health insurance system. In this article, four of the first BfArM-listed DiGA manufacturers report on their experiences with the BfArM Fast-Track procedure for DiGA, which enables listing from the time of application in just three months.Regarding the DiGA Fast-Track procedure and the cooperation with the BfArM, overall positive experiences are reported. However, applicants need to consider some points before and during the application process as well as after the positive decision. Before submitting the application, it is advisable to conduct audits to ensure that all requirements are met. BfArM consultations should be used, especially to clarify questions regarding proof of positive supply effect. Manufacturers should be prepared for numerous queries and follow-up requests from BfArM and be able to respond quickly. In the case of ambiguities, direct contact should be made with the BfArM. Manufacturers should note that sales of their product will not automatically follow a positive decision, as the medical profession still needs to be informed more fundamentally about DiGA and the path from the prescription to the activation of DiGA is currently still cumbersome. Manufacturers should also be prepared for continued interaction with BfArM after listing.Overall, manufacturers are recommended to cooperate early, proactively, openly, and closely with the BfArM because they themselves are liable for the information they provide in the application and the BfArM does not check all of it in detail.

The phase diagram of sodium chloride (NaCl) under laser shock compression has been studied at Linac Coherent Light Source (LCLS) at the x-ray free-electron laser facility. Both solid–solid (B1 → B2) and solid–liquid (B2 → liquid) transitions have been observed along the Hugoniot over nanosecond time scales. By combining structural measurements through in situ x-ray diffraction, pressure determination through velocimetry, and a thermal equation-of-state, the shock-compressed data are used to constrain the phase diagram of NaCl. Transformation into the B2 phase is found to occur at 28(2) GPa, and B2–liquid coexistence is observed between 54(4) and 66(6) GPa, with near full melt at 66(6) GPa. Late-time pressure release from an initial shocked B2-state results in a B2 → B1 back transformation. Our results show agreement with previous static compression data, suggesting that the time scale for melting is very rapid and that equilibrium states in NaCl are being accessed over nanosecond time scales. A multiphase equation-of-state description of NaCl incorporated into a one-dimensional hydrocode is used to interpret pressure and temperature evolution over these rapid time scales.

We present structure and equation of state (EOS) measurements of biaxially orientated polyethylene terephthalate (PET, $$({\hbox {C}}_{10} {\hbox {H}}_8 {\hbox {O}}_4)_n$$ ( C 10 H 8 O 4 ) n , also called mylar) shock-compressed to ($$155 \pm 20$$ 155 ± 20 ) GPa and ($$6000 \pm 1000$$ 6000 ± 1000 ) K using in situ X-ray diffraction, Doppler velocimetry, and optical pyrometry. Comparing to density functional theory molecular dynamics (DFT-MD) simulations, we find a highly correlated liquid at conditions differing from predictions by some equations of state tables, which underlines the influence of complex chemical interactions in this regime. EOS calculations from ab initio DFT-MD simulations and shock Hugoniot measurements of density, pressure and temperature confirm the discrepancy to these tables and present an experimentally benchmarked correction to the description of PET as an exemplary material to represent the mixture of light elements at planetary interior conditions.

For LCLS-II, we have developed fluorescence intensity monitors and power meters as intensity monitors. The Fluorescence Intensity Monitor (FIM) provides the non-invasive, pulse-by-pulse normalization of experiments. For the LCLS-II instruments, the diagnostic was constructed with an array of four microchannel plate assemblies and four avalanche photodiodes. The diagnostics are being installed in each Kirkpatrick Baez mirror chamber. The noise of the diagnostic will be evaluated against a goal of 1 %. The X-ray power meter delivers average power values. For the LCLS-II instruments, a power meter was selected compatible with high average power. In the LCLS-II instruments, power meters are being installed with each profile monitor in order to evaluate the transmission along the X-ray transport. A calibration of a set of power meters was carried out against a gas monitor detector at FLASH. In addition for all the power meters, a relative calibration was performed with a visible light source. At the endstations, a power meter will determined the pulse energy at the sample.

Since October 2020, the first digital health applications (DiGA) have been listed with the Federal Institute for Drugs and Medical Devices (BfArM) and can be prescribed by physicians and psychotherapists in the statutory health insurance system. In this article, four of the first BfArM-listed DiGA manufacturers report on their experiences with the BfArM Fast-Track procedure for DiGA, which enables listing from the time of application in just three months.Regarding the DiGA Fast-Track procedure and the cooperation with the BfArM, overall positive experiences are reported. However, applicants need to consider some points before and during the application process as well as after the positive decision. Before submitting the application, it is advisable to conduct audits to ensure that all requirements are met. BfArM consultations should be used, especially to clarify questions regarding proof of positive supply effect. Manufacturers should be prepared for numerous queries and follow-up requests from BfArM and be able to respond quickly. In the case of ambiguities, direct contact should be made with the BfArM. Manufacturers should note that sales of their product will not automatically follow a positive decision, as the medical profession still needs to be informed more fundamentally about DiGA and the path from the prescription to the activation of DiGA is currently still cumbersome. Manufacturers should also be prepared for continued interaction with BfArM after listing.Overall, manufacturers are recommended to cooperate early, proactively, openly, and closely with the BfArM because they themselves are liable for the information they provide in the application and the BfArM does not check all of it in detail.Seit Oktober 2020 sind die ersten digitalen Gesundheitsanwendungen (DiGA) beim Bundesinstitut für Arzneimittel und Medizinprodukte (BfArM) gelistet und können in der gesetzlichen Krankenversicherung von Ärzten und Psychotherapeuten verordnet werden. 4 der ersten BfArM-gelisteten DiGA-Hersteller berichten in diesem Artikel über ihre Erfahrungen mit dem BfArM-Fast-Track-Verfahren für DiGA, das eine Listung ab Antragsstellung in nur 3 Monaten ermöglicht.Bezüglich des DiGA-Fast-Track-Verfahrens und der Zusammenarbeit mit dem BfArM werden insgesamt positive Erfahrungen berichtet. Von den Antragstellern sind aber vor und während des Antragsverfahrens sowie nach der positiven Bescheidung einige Punkte zu beachten. Vor der Antragseinreichung ist es empfehlenswert, Audits durchzuführen, um sicherzugehen, dass alle Anforderungen erfüllt sind. BfArM-Beratungen sollten genutzt werden, insbesondere um Fragen zum Nachweis des positiven Versorgungseffekts zu klären. Hersteller sollten sich auf zahlreiche Rückfragen und Nachforderungen des BfArM einstellen und schnell darauf reagieren können. Bei Unklarheiten sollte direkt Kontakt mit dem BfArM aufgenommen werden. Hersteller sollten beachten, dass sich nach der positiven Bescheidung der Umsatz für ihr Produkt nicht automatisch einstellt, da die Ärzteschaft noch grundlegender über DiGA informiert werden muss und sich der Weg vom Rezept bis zur Freischaltung der DiGA derzeit noch umständlich gestaltet. Hersteller sollten sich zudem darauf einstellen, dass sich die Interaktion mit dem BfArM nach der Listung fortsetzt.Insgesamt wird den Herstellern eine frühe, proaktive, offene und enge Zusammenarbeit mit dem BfArM empfohlen, auch weil sie selbst für ihre Angaben im Antrag haften und das BfArM diese nicht alle im Detail prüft.

Combining an x-ray free electron laser with a high-power laser driver enables the study of equations-of-state, high strain-rate deformation processes, structural phase transitions, and transformation pathways as a function of pressure to hundreds of GPa along different thermodynamic compression paths. Future high repetition-rate laser operation will enable data to be accumulated at >1 Hz, which poses a number of experimental challenges, including the need to rapidly replenish the target. Here, we present a combined shock compression and an x-ray diffraction study on epoxy (50% vol.)-crystalline grains (50% vol.) slurry targets, which can be fashioned into extruded ribbons for high repetition-rate operation. For shock-loaded NaCl-slurry samples, we observe pressure, density, and temperature states within the embedded NaCl grains consistent with observations from shock-compressed single-crystal NaCl.

Defect clusters in ion-irradiated tungsten are characterized by X-ray diffuse scattering. Single crystal tungsten samples are irradiated at 300 K by 0.5–5 MeV copper ions with total doses of 0.2, 0.6, 2, and 5 displacements per atom (DPA). Analysis of the diffuse scattering intensities allows the determination of the concentration of vacancy- and interstitial-type dislocation loops as a function of loop radius for each sample. More vacancies than interstitials are observed in each sample, and the radius of the vacancy loops increases with irradiation dose. For the 0.2DPA sample the average vacancy loop radius is 10.1 ± 3.0 A with a defect density (counting all atoms in the loops) of ( 10.2 ± 1.5 ) × 10 − 4 per tungsten atom, increasing to an average loop radius of 16.1 ± 3.1 A at a density of ( 8.5 ± 1.0 ) × 10 − 4 per tungsten atom for the 5DPA sample.

The electron-ion relaxation dynamics in warm dense iron were investigated by time-resolved x-ray absorption near-edge spectroscopy (XANES). A novel analysis, combining ab initio density functional theory (DFT) and two temperature model (TTM) simulations, was developed to calculate the x-ray absorption spectra as a function of delay time. Here we present experimental evidence of changes at the XAS L3 edge of iron that are consistent with the reduction of the electron-phonon coupling under warm dense matter conditions. The experimental results are in agreement with the model that takes both the electron (${T}_{e}$) and the ion temperature (${T}_{i}$) dependence of the thermophysical properties into consideration, while models where either constant electron-phonon coupling factor (G) or only ${T}_{e}$-dependent G are used do not agree with the observed relaxation dynamics of iron.

Ronchi testing of a focused electromagnetic wave has in the last few years been used extensively at X-ray free-electron laser (FEL) facilities to qualitatively evaluate the wavefront of the beam. It is a quick and straightforward test, is easy to interpret on the fly, and can be used to align phase plates that correct the focus of aberrated beams. In general, a single Ronchigram is not sufficient to gain complete quantitative knowledge of the wavefront. However the compound refractive lenses that are commonly used at X-ray FELs exhibit a strong circular symmetry in their aberration, and this can be exploited. Here, a simple algorithm that uses a single recorded Ronchigram to recover the full wavefront of a nano-focused beam, assuming circular symmetry, is presented, and applied to experimental measurements at the Matter in Extreme Conditions instrument at the Linac Coherent Light Source.

Laser power meters are being developed as a compact X-ray power diagnostic for LCLS-II and are characterized for their responsivity, linearity and vacuum compatibility. The power meters are calibrated against X-ray photodiodes and a gas monitor detector., For the LCLS-II X-ray instruments, laser power meters are being developed as compact X-ray power diagnostics to operate at soft and tender X-ray photon energies. These diagnostics can be installed at various locations along an X-ray free-electron laser (FEL) beamline in order to monitor the transmission of X-ray optics along the beam path. In addition, the power meters will be used to determine the absolute X-ray power at the endstations. Here, thermopile power meters, which measure average power, and have been chosen primarily for their compatibility with the high repetition rates at LCLS-II, are evaluated. A number of characteristics in the soft X-ray range are presented including linearity, calibrations conducted with a photodiode and a gas monitor detector as well as ultra-high-vacuum compatibility tests using residual gas analysis. The application of these power meters for LCLS-II and other X-ray FEL sources is discussed.

The Icarus camera system, combining a sensor developed by Sandia and readout electronics by LLNL, provides 0.5 Hz bursts of four frames with 3 ns separation. The sensor has 1024×512 25 μm pixels and is 25 μm thick. The system was developed for single line-of-sight measurements at the ns time scale for electrons and X-rays at facilities such as NIF. We report on initial tests of the Icarus system with hard X-rays pulse pairs with nanosecond time spacings at the LCLS, a newly available beam mode. We describe noise, gate profiles, gain, cross-talk, persistence, linearity, and quantum efficiency for the first version of the sensor. We present evidence of the suitability of the system for science measurements at a free electron laser with an X-ray pump X-ray probe experiment. We expect further developments of the technology to allow use of 350 ps bunch separation from the LCLS accelerator and, with a pulsed delay tube like DIXIE, to eventually reach sub-25 ps time-resolved X-ray imaging of processes such as plasma evolution.

For the LCLS-II X-ray instruments, we have developed laser power meters as compact X-ray power monitors. A calibration of the responsivity of the power meters was carried out against a silicon photodiode with synchrotron radiation and a gas monitor detector with FEL X-rays. A manipulator with two power meters was installed in various locations at the LCLS. In the LCLS front end, the power meters were compared with the gas detectors, which are calibrated by the electron energy loss method. The agreement between the power meters and the gas detectors was better than 20% at 1500 eV with the pulse energy measured by the gas detectors higher than that from the power meters. In the AMO instrument, the power meters evaluated the improvement in beamline transmission caused by the oxygen plasma cleaning of the Kirkpatrick-Baez mirrors. Measurements were also conducted one and two years later to observe the effect of further contamination of the optical surfaces. Finally at the SXR instrument, the power meters determined the pulse energy at the sample for a beamtime, where the X-ray intensity was an important parameter.

Degenerate plasmas, in which quantum effects dictate the behavior of free electrons, are ubiquitous on earth and throughout space. Transitions between bound and free electron states determine basic plasma properties, yet the effects of degeneracy on these transitions have only been theorized. Here, we use an x-ray free electron laser to create and characterize a degenerate plasma. We observe a core electron fluorescence spectrum that cannot be reproduced by models that ignore free electron degeneracy. We show that degeneracy acts to restrict the available electron energy states, thereby slowing the rate of transitions to and from the continuum. We couple degeneracy and bound electron dynamics in an existing collisional-radiative code, which agrees well with observations. The impact of the shape of the cross section, and hence the magnitude of the correction due to degeneracy, is also discussed. This study shows that degeneracy in plasmas can significantly influence experimental observables such as the emission spectra, and that these effects can be included parametrically in well-established atomic physics codes. This work narrows the gap in understanding between the condensed-matter and plasma phases, which coexist in myriad scenarios.

A prefocusing compound refractive lens was implemented for the Matter under Extreme Conditions Instrument at the Linac Coherent Light Source. A significant improvement in the beamline transmission was calculated and observed at 5 keV., The performance of X-ray free-electron laser beamlines may be limited by the angular aperture. Compound refractive lenses (CRLs) can be employed to prefocus the X-ray beam, thereby increasing the beamline transmission. A prefocusing CRL was implemented in the X-ray transport of the Matter under Extreme Conditions Instrument at the Linac Coherent Light Source. A significant improvement in the beamline transmission was calculated over the 3–10 keV photon energy range. At 5 keV, the relative X-ray intensity was measured and a factor of four increase was seen in the beamline transmission. The X-ray focus was also determined by the ablation imprint method.

A fluorescence intensity monitor has been developed for the non-invasive, pulse-by-pulse normalization of LCLS-II experiments. The linearity, noise and position sensitivity of the detectors have been characterized., For LCLS-II, a fluorescence intensity monitor for the non-invasive, pulse-by-pulse normalization of experiments has been developed. A prototype diagnostic was constructed with a microchannel plate assembly and two photodiodes. The diagnostic was then installed in the LCLS SXR instrument Kirkpatrick–Baez mirror chamber with the detectors located above the vertically reflecting mirror. The linearity, noise and position sensitivity of the detectors have been characterized. The photodiode responsivity is suitable for high pulse energies. The microchannel plate detector shows sufficient responsivity over a wide range of pulse energies. The relative signal from the two photodiodes provides a sensitive measure of the X-ray beam position. The fluorescence intensity monitor provides intensity normalization while being compatible with high incident power, a 0.93 MHz repetition rate and ultra-high vacuum.

© 2018 Author(s). Diamond formation in polystyrene (C8H8)n, which is laser-compressed and heated to conditions around 150 GPa and 5000 K, has recently been demonstrated in the laboratory [Kraus et al., Nat. Astron. 1, 606-611 (2017)]. Here, we show an extended analysis and comparison to first-principles simulations of the acquired data and their implications for planetary physics and inertial confinement fusion. Moreover, we discuss the advanced diagnostic capabilities of adding high-quality small angle X-ray scattering and spectrally resolved X-ray scattering to the platform, which shows great prospects of precisely studying the kinetics of chemical reactions in dense plasma environments at pressures exceeding 100 GPa.

A description of the Soft X-ray Research instrument (SXR) at the Linac Coherent Light Source is given. Recent scientific highlights illustrate the wide variety of experiments and detectors that can be accommodated at SXR., The Soft X-ray Research instrument provides intense ultrashort X-ray pulses in the energy range 280–2000 eV. A diverse set of experimental stations may be installed to investigate a broad range of scientific topics such as ultrafast chemistry, highly correlated materials, magnetism, surface science, and matter under extreme conditions. A brief description of the main instrument components will be given, followed by some selected scientific highlights.

The recent advent of X-ray free-electron lasers (XFELs) marks the beginning of a new era in X-ray science, providing coherent ultrafast X-ray pulses with unprecedented peak brightness. The first generation of these facilities (FLASH, LCLS, and SACLA) have already had tremendous scientific impact, and numerous similar facilities are now being developed around the world. These first-generation XFELs are based on pulsed-radio frequency (RF) accelerator technology with limited repetition rates. Thus, they provide only modest average brightness, comparable to or lower than that available from existing storage rings, and this limits their impact in key areas of science. A new generation of XFELs is now under development, exploiting continuous-wave RF superconducting accelerator technology (CW-SCRF) to provide ultrafast X-ray pulses up to MHz repetition rates in a uniform or programmable time structure. This chapter highlights some compelling new science opportunities that will be enabled by such high-repetition-rate XFELs. These opportunities have been identified and developed through numerous workshops over the past decade. In February 2015, a series of workshops were held at SLAC focusing on the new science opportunities that will be enabled by LCLS-II, which will provide ultrafast X-rays in the 0.25–5 keV range at repetition rates up to 1 MHz.

Interaction of short-wavelength free-electron laser (FEL) beams with matter is undoubtedly a subject to extensive investigation in last decade. During the interaction various exotic states of matter, such as warm dense matter, may exist for a split second. Prior to irreversible damage or ablative removal of the target material, complicated electronic processes at the atomic level occur. As energetic photons impact the target, electrons from inner atomic shells are almost instantly photo-ionized, which may, in some special cases, cause bond weakening, even breaking of the covalent bonds, subsequently result to so-called non-thermal melting. The subject of our research is ablative damage to lead tungstate (PbWO4) induced by focused short-wavelength FEL pulses at different photon energies. Post-mortem analysis of complex damage patterns using the Raman spectroscopy, atomic-force (AFM) and Nomarski (DIC) microscopy confirms an existence of non-thermal melting induced by high-energy photons in the ionic monocrystalline target. Results obtained at Linac Coherent Light Source (LCLS), Free-electron in Hamburg (FLASH), and SPring-8 Compact SASE Source (SCSS) are presented in this Paper.

For the LCLS-II instruments we are developing laser power meters as compact intensity monitors that can operate at soft and tender X-ray photon energies. There is a need to monitor the relative X-ray intensity at various locations along an X-ray FEL beamline in order to observe a possible decrease in the reflectivity of X-ray mirrors. In addition for experiments, it is valuable to know the absolute intensity at the sample. There are two types of laser power meters based on thermopile and pyroelectric sensors. The thermopile power meters measure an average temperature and are compatible with the high repetition rates of LCLS-II. Pyroelectric power meters provide a pulse-by-pulse response. Ultra-high vacuum compatibility is being tested by residual gas analysis. An in-house development beamtime is being conducted at the LCLS SXR instrument. Measurements using both thermopile and pyroelectric power meters will be conducted at a set of photon energies in the soft X-ray range. The detectors’ response will be compared with the gas monitor detector installed at the SXR instrument.

We report on the x-ray absorption of Warm Dense Matter experiment at the FLASH Free Electron Laser (FEL) facility at DESY. The FEL beam is used to produce Warm Dense Matter with soft x-ray absorption as the probe of electronic structure. A multilayer-coated parabolic mirror focuses the FEL radiation, to spot sizes as small as 0.3μm in a ∼15fs pulse of containing >10 12 photons at 13.5 nm wavelength, onto a thin sample. Silicon photodiodes measure the transmitted and reflected beams, while spectroscopy provides detailed measurement of the temperature of the sample. The goal is to measure over a range of intensities approaching 10 18 W/cm 2. Experimental results will be presented along with theoretical calculations. A brief report on future FEL efforts will be given. © 2009 SPIE.

We have studied a solid-to-plasma transition by irradiating Al foils with the FLASH free electron laser at intensities up to 10(16) W/cm(2). Intense XUV self-emission shows spectral features that are consistent with emission from regions of high density, which go beyond single inner-shell photoionization of solids. Characteristic features of intrashell transitions allowed us to identify Auger heating of the electrons in the conduction band occurring immediately after the absorption of the XUV laser energy as the dominant mechanism. A simple model of a multicharge state inverse Auger effect is proposed to explain the target emission when the conduction band at solid density becomes more atomiclike as energy is transferred from the electrons to the ions. This allows one to determine, independent of plasma simulations, the electron temperature and density just after the decay of crystalline order and to characterize the early time evolution.

Applied physics letters 109(3), 031108 (2016). doi:10.1063/1.4959256, We present results from time-resolved X-ray imaging and inelastic scattering on collective excitations. These data are then employed to infer the mass density evolution within laser-driven shock waves. In our experiments, thin carbon foils are first strongly compressed and then driven into a dense state by counter-propagating shock waves. The different measurements agree that the graphite sample is about twofold compressed when the shock waves collide, and a sharp increase in forward scattering indicates disassembly of the sample 1 ns thereafter. We can benchmark hydrodynamics simulations of colliding shock waves by the X-ray scattering methods employed., Published by American Inst. of Physics, Melville, NY

© 2016, Nature Publishing Group. All rights reserved. Experimental investigation of electron-ion coupling and electron heat capacity of copper in warm and dense states are presented. From time-resolved x-ray absorption spectroscopy, the temporal evolution of electron temperature is obtained for non-equilibrium warm dense copper heated by an intense femtosecond laser pulse. Electron heat capacity and electron-ion coupling are inferred from the initial electron temperature and its decrease over 10 ps. Data are compared with various theoretical models.

X-ray absorption spectroscopy (XAS) is a versatile technique for studying the electronic structure and/or the local geometry of matter, and time-resolved XAS has been developed into a powerful tool for studying the dynamics of materials [1, 2]. The temporal resolution of this technique is usually determined by the X-ray pulse duration in pump and probe geometries. Although this technique has been developed in the synchrotron environment and takes advantage of existing X-ray beamlines, the study of ultrafast dynamics on time scales on the order of a picosecond or faster is limited because typical pulse durations from third-generation light sources is on the order of tens of picoseconds. In addition, XAS typically requires the integration of a large number of X-ray pulses to get quality data. These features make it difficult to apply this technique to research areas in which samples undergo irreversible processes.

Warm dense conditions in titanium foils irradiated with intense femtosecond laser pulses are diagnosed using an x-ray imaging spectroscopy technique. The line shapes of radially resolved titanium Kα spectra are measured with a toroidally bent GaAs crystal and an x-ray charge-coupled device. Measured spectra are compared with the K-shell emissions modeled using an atomic kinetics - spectroscopy simulation code. Kα line shapes are strongly affected by warm (5-40 eV) bulk electron temperatures and imply multiple temperature distributions in the targets. The spatial distribution of temperature is dependent on the target thickness, and a thin target shows an advantage to generate uniform warm dense conditions in a large area.

W/C and Co/SiO 2 multilayer laminar-type holographic plane gratings (groove density 1/σ = 1200 lines/mm) in the 1–8 keV region are developed. For the Co/SiO 2 grating the diffraction efficiencies of 0.41 and 0.47 at 4 and 6 keV, respectively, and for the W/C grating 0.38 at 8 keV are observed. Taking advantage of the outstanding high diffraction efficiencies into practical soft X-ray spectrographs a Mo/SiO 2 multilayer varied-line-spacing (VLS) laminar-type spherical grating (1/σ = 2400 lines/mm) is also developed for use with a flat field spectrograph in the region of 1.7 keV. For the Mo/SiO 2 multilayer grating the diffraction efficiencies of 0.05–0.20 at 0.9–1.8 keV are observed. The FWHMs of the measured line profiles of Hf-Mα 1 (1644.6 eV), Si-Kα 1 (1740.0 eV), and W-Mα 1 (1775.4 eV) are 13.7 eV, 8.0 eV, and 8.7 eV, respectively.

Free-electron lasers (FELs) have invigorated physics research, but novel sources require novel means of beam characterization as an integral part of any experiment. In this study, desorption imprints in plastic yield transverse intensity profiles of an x-ray FEL beam, from which the authors recover the complex electric-field profile and coherence properties of the focused beam. This approach will inform not only experiments in coherent diffraction imaging, x-ray microscopy, and high-energy-density physics, but also the development of tomorrow's x-ray laser sources.

Warm dense matter (WDM), which falls in the category between plasmas and condensed matter, is expected to exist in planetary interiors. Now, researchers use an X-ray laser to observe the transition to WDM.

The rate at which atoms and ions within a plasma are further ionized by collisions with the free electrons is a fundamental parameter that dictates the dynamics of plasma systems at intermediate and high densities. While collision rates are well known experimentally in a few dilute systems, similar measurements for nonideal plasmas at densities approaching or exceeding those of solids remain elusive. Here we describe a spectroscopic method to study collision rates in solid-density aluminium plasmas created and diagnosed using the Linac Coherent light Source free-electron X-ray laser, tuned to specific interaction pathways around the absorption edges of ionic charge states. We estimate the rate of collisional ionization in solid-density aluminium plasmas at temperatures ~30 eV to be several times higher than that predicted by standard semiempirical models.

The Linac Coherent Light Source has added a self-seeding capability to the soft x-ray range using a grating monochromator system. We report the demonstration of soft x-ray self-seeding with a measured resolving power of 2000–5000, wavelength stability of 10$^{−4}$, and an increase in peak brightness by a factor of 2–5 across the photon energy range of 500–1000 eV. By avoiding the need for a monochromator at the experimental station, the self-seeded beam can deliver as much as 50-fold higher brightness to users.

International audience; The time evolution of the electron structure is investigated in a molybdenum foil heated up to the warm dense matter regime by a femtosecond laser pulse, through time-resolved x-ray absorption near-edge spectroscopy. Spectra are measured with independent characterizations of temperature and density. They are successfully compared with ab initio quantum molecular dynamic calculations. We demonstrate that the observed white line in the L-3 edge reveals the time evolution of the electron density of state from the solid to the hot (a few eV) and expanding liquid. The data indicate a highly nonequilibrated state, 5 ps after heating.

A description of the Matter in Extreme Conditions instrument at the Linac Coherent Light Source is given. Recent scientific highlights illustrate phase-contrast imaging of shock waves, X-ray Thomson scattering and X-ray diffraction of shocked materials., The LCLS beam provides revolutionary capabilities for studying the transient behavior of matter in extreme conditions. The particular strength of the Matter in Extreme Conditions instrument is that it combines the unique LCLS beam with high-power optical laser beams, and a suite of dedicated diagnostics tailored for this field of science. In this paper an overview of the beamline, the capabilities of the instrumentation, and selected highlights of experiments and commissioning results are presented.

We present a setup which allows the measurement of time-resolved x-ray absorption spectra with picosecond temporal resolution on liquid samples at the Advanced Light Source at Lawrence Berkeley National Laboratories. The temporal resolution is limited by the pulse width of the synchrotron source. We characterize the different sources of noise that limit the experiment and present a single-pulse detection scheme.

Review of scientific instruments 88(5), 053501 (2017). doi:10.1063/1.4982166, Tuning the energy of an x-ray probe to an absorption line or edge can provide material-specific measurements that are particularly useful for interfaces. Simulated hard x-ray images above the Fe K-edge are presented to examine ion diffusion across an interface between Fe$_2$O$_3$ and SiO$_2$ aerogel foam materials. The simulations demonstrate the feasibility of such a technique for measurements of density scale lengths near the interface with submicron spatial resolution. A proof-of-principle experiment is designed and performed at the Linac coherent light source facility. Preliminary data show the change of the interface after shock compression and heating with simultaneous fluorescence spectra for temperature determination. The results provide the first demonstration of using x-ray imaging at an absorption edge as a diagnostic to detect ultrafast phenomena for interface physics in high-energy-density systems., Published by American Institute of Physics, [S.l.]

High-intensity x-ray pulses from an x-ray free-electron laser are used to heat and probe a solid-density aluminum sample. The photon-energy-dependent transmission of the heating beam is studied through the use of a photodiode. Saturable absorption is observed, with the resulting transmission differing significantly from the cold case, in good agreement with atomic-kinetics simulations.

The intensities within the focal spots of the output of recently developed X-ray sources based on free-electron-laser (FEL) technology are so great that atoms within the focal region can potentially absorb several photons during the few tens of femtosecond X-ray pulse. Furthermore, the duration of the FEL X-ray pulse is comparable to the Auger decay times of inner-shell holes created by the X-rays themselves. We report here how such a scenario can lead to opacity broadening of the fluorescence radiation emitted by the hot, dense plasma, which is created as a result of the X-radiation focussed onto a solid target, and in particular present calculations of the broadening of the Kα emission in a solid-density aluminium target, produced when the FEL photon energy is tuned below the Al K-edge, but is resonant with the Kα transition. © 2014 Elsevier B.V.

International audience; The rapidly growing ultrafast science with X-ray lasers unveils atomic scale processes with unprecedented time resolution bringing the so called "molecular movie'' within reach. X-ray absorption spectroscopy is one of the most powerful x-ray techniques providing both local atomic order and electronic structure when coupled with ad-hoc theory. Collecting absorption spectra within few x-ray pulses is possible only in a dispersive setup. We demonstrate ultrafast time-resolved measurements of the LIII-edge x-ray absorption near-edge spectra of irreversibly laser excited Molybdenum using an average of only few x-ray pulses with a signal to noise ratio limited only by the saturation level of the detector. The simplicity of the experimental set-up makes this technique versatile and applicable for a wide range of pump-probe experiments, particularly in the case of non-reversible processes.

This paper reports novel measurements of x-ray optical radiation on an absolute scale from the intense and ultra-short radiation generated in the soft x-ray regime of a free electron laser. We give a brief description of the detection principle for radiation measurements which was specifically adapted for this photon energy range. We present data characterizing the soft x-ray instrument at the Linac Coherent Light Source (LCLS) with respect to the radiant power output and transmission by using an absolute detector temporarily placed at the downstream end of the instrument. This provides an estimation of the reflectivity of all x-ray optical elements in the beamline and provides the absolute photon number per bandwidth per pulse. This parameter is important for many experiments that need to understand the trade-offs between high energy resolution and high flux, such as experiments focused on studying materials via resonant processes. Furthermore, the results are compared with the LCLS diagnostic gas detectors to test the limits of linearity, and observations are reported on radiation contamination from spontaneous undulator radiation and higher harmonic content.

Femtosecond X-ray science is a new frontier in ultrafast research in which time-resolved measurement techniques are applied with X-ray pulses to investigate structural dynamics at the atomic scale on the fundamental time scale of an atomic vibrational period (∼100 fs). This new research area depends critically on the development of suitable femtosecond X-ray sources with the appropriate flux (ph/(s·0.1% BW)), brightness (ph/(s·mm 2 ·mrad 2 ·0.1% BW)), and tunability for demanding optical/X-ray pump probe experiments. In this paper we review recently demonstrated techniques for generating femtosecond X-rays via interaction between femtosecond laser pulses and relativistic electron beams. We give an overview of a novel femtosecond X-ray source that is proposed based on a linear accelerator combined with X-ray pulse compression.

The generation of femtosecond X-ray pulses will have important scientific applications by enabling the direct measurement of atomic motion and structural dynamics in condensed matter on the fundamental time scale of a vibrational period. Interaction of femtosecond laser pulses with relativistic electron beams is an effective approach to generating femtosecond pulses of X-rays. In this paper we present recent results from proof-of-principle experiments in which 300 fs pulses are generated from a synchrotron storage ring by using an ultrashort optical pulse to create femtosecond time structure on the stored electron bunch. A previously demonstrated approach for generating femtosecond X-rays via Thomson scattering between terawatt laser pulses and relativistic electrons is reviewed and compared with storage-ring based schemes.

A technique is proposed for producing high average intensity X-ray radiation from a storage ring for studies of the ultrafast phenomena on a subpicosecond time scale. Two RF cavity accelerating structures excited in the E 110 mode can be installed in a storage ring to create vertical displacements of electrons correlated with their longitudinal position in the bunch. The magnitude of these displacements can be sufficient for the X-ray radiation of the electron bunch between accelerating structures to be viewed as produced by a large number of independent sources, each of a subpicosecond duration.

We report rotational-resolved single-photon threshold photoelectron and pulsed field ionization zero kinetic energy (PFI–ZEKE) photoelectron (PE) spectra of O2 in the energy range of 18.1–20.2 eV measured using high-resolution monochromatized multibunch undulator synchrotron radiation. The PFI–ZEKE PE bands for O2+(b 4Σg−, v+=0–9) have been simulated using the Buckingham–Orr–Sichel model derived for rotationally resolved single-photon ionization cross-sections. Only the ΔN=−2, 0 and +2 (or O, Q and S) rotational branches are observed for these PFI–ZEKE PE bands, indicating that the outgoing electron continuum channels with angular momenta l=1 and 3 dominate in the threshold ionization transitions O2+(b 4Σg−, v+=0–9, N+)←O2(X 3Σg−, v″=0, N″). The relative rotational branch intensities for O2+(b 4Σg−, v+=4 and 5) are found to be drastically different from those for O2+(b 4Σg−, v+=0–3, 6 and 7). Considering that the energies of O2+(b 4Σg−, v+=4 and 5) are close to the dissociation limit of O+(4S)+O(3P) and that the crossing location of the O2+(b 4Σg−) and d 4Σg+ potential curves is shown to be in the vicinity of O2+(b 4Σg−, v+=4 and 5), we suggest that the latter observation is the result of predissociative perturbations by the d 4Σg+ state. Within the uncertainties of this experiment, the ionization energies for the formation of O2+(b 4Σg−, v+=0–9, N+=1) can be satisfactorily characterized using a Morse potential. The effective lifetimes for high-n Rydberg states converging to O2+(b 4Σg−, v+=0, 2–5) prepared in the present experiment are nearly constant with values in the range of 1.8–2.0 μs. The observation that the effective lifetimes for high-n Rydberg states converging to O2+(b 4Σg−, v+=4 and 5) are significantly longer than the known dissociative lifetimes of the corresponding ionic states is in accordance with the expectation that the couplings between the O2+ ion core and the high-n Rydberg electron involved are negligibly small.

We present here the assignment and simulation of rotational transitions for the H2+(X 2Σg+, v+=0, 2, 9 and 11) vibronic bands using the Buckingham–Orr–Sichel (BOS) model. The simulation shows that perturbation of PFI-PE rotational line intensities due to near-resonance autoionization decreases as v+ increases. Experimental rotational constants for H2+(X 2Σg+, v+=0, 2, 9 and 11) are determined with higher accuracy than those obtained in previous He I and Ne I photoelectron studies. In agreement with previous experimental and theoretical investigations, only the ΔN=0 and ±2 rotational branches are observed in the PFI-PE spectrum for H2.

We have improved a newly developed experimental scheme for high resolution pulsed field ionization photoelectron (PFI-PE) studies [Hsu et al., Rev. Sci. Instrum. (in press)] using the high resolution monochromatized multibunch undulator synchrotron source of the Chemical Dynamics Beamline at the Advanced Light Source. This improved scheme makes possible PFI-PE measurements with essentially no contamination by background electrons arising from direct photoionization and prompt autoionization processes. We present here a preliminary analysis of the rotationally resolved PFI-PE spectrum for O2 obtained at a resolution of 0.5 meV (full-width-at-half-maximum) in the photon energy range of 18.1–19.4 eV, yielding accurate ionization energies for the transitions O2+(b 4Σg−, v+=0–9, N+=1)←O2(X 3Σg−, v=0, N=1).

At the Advanced Light Source an undulator beamline, with an energy range from 6 to 30 eV, has been constructed for chemical dynamics experiments. The higher harmonics of the undulator are suppressed by a novel, windowless gas filter. In one branchline high-flux, 2% bandwidth radiation is directed toward an end station for photodissociation and crossed molecular-beam experiments. A photon flux of 1016 photon/s has been measured at this end station. In a second branchline a 6.65 m off-plane Eagle monochromator delivers narrow bandwidth radiation to an end station for photoionoization studies. At this second end station a peak flux of 3×1011 was observed for 25 000 resolving power. This monochromator has achieved a resolving power of 70 000 using a 4800 grooves/mm grating, one of the highest resolving powers obtained by a vacuum ultraviolet monochromator.