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European XFEL is an international facility providing hard and soft x-ray free-electron laser radiation for user experiments with a wide range of scientific applications. Its superconducting linear accelerator enables high repetition rate experiments with a broad range of x-ray pulse delivery patterns. The combination of time-resolved experiments, providing access to the time-domain from sub-femtoseconds to milliseconds, with atomic resolution x-ray geometric and electronic structure determination methods is responsible for the bulk of scientific applications of European XFEL. In addition, the extreme x-ray intensities and coherence properties open new methods for studying matter out of equilibrium. After start of operation in 2017, the facility now harvests scientific applications with impact to the challenge areas climate and energy, health, environment and sustainability, and digitalization. Extensions of European XFEL aim to increase performance and capabilities for new scientific applications. An upgrade of the facility in the early 2030s will increase the applicability of European XFEL to solid materials and provide dedicated instruments for improved conditions in specific research fields.

International audience; We describe a setup for performing inelastic X-ray scattering and X-ray diffraction measurements at the Matter in Extreme Conditions (MEC) endstation of the Linac Coherent Light Source. This technique is capable of performing high-, meV-resolution measurements of dynamic ion features in both crystalline and non-crystalline materials. A four-bounce silicon (533) monochromator was used in conjunction with three silicon (533) diced crystal analyzers to provide an energy resolution of ∼50 meV over a range of ∼500 meV in single shot measurements. In addition to the instrument resolution function, we demonstrate the measurement of longitudinal acoustic phonon modes in polycrystalline diamond. Furthermore, this setup may be combined with the high intensity laser drivers available at MEC to create warm dense matter and subsequently measure ion acoustic modes.

We report on soft X-ray scattering experiments on cryogenic hydrogen and simple metal samples. As a source of intense, ultrashort soft X-ray pulses we have used free-electron laser radiation at 92 eV photon energy from FLASH at DESY, Hamburg. X-ray pulses with energies up to 150 μJ and durations 15-50 fs provide interaction with the sample leading simultaneously to plasma formation and scattering. Experiments exploiting both of these interactions have been carried out, using the same experimental setup. Firstly, recording of soft X-ray inelastic scattering from near-solid density hydrogen plasmas at few electron volt temperatures confirms the feasibility of this diagnostics technique. Secondly, the soft X-ray excitation of few electron volt solid-density plasmas in bulk metal samples could be studied by recording soft X-ray line and continuum emission integrated over emission times from fs to ns. © 2009 Elsevier B.V.

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.

The ability to fully characterize ultrashort, ultra-intense X-ray pulses at free-electron lasers (FELs) will be crucial in experiments ranging from single-molecule imaging to extreme-timescale X-ray science. This issue is especially important at current-generation FELs, which are primarily based on self-amplified spontaneous emission and radiate with parameters that fluctuate strongly from pulse to pulse. Using single-cycle terahertz pulses from an optical laser, we have extended the streaking techniques of attosecond metrology to measure the temporal profile of individual FEL pulses with 5 fs full-width at half-maximum accuracy, as well as their arrival on a time base synchronized to the external laser to within 6 fs r.m.s. Optical laser-driven terahertz streaking can be utilized at any X-ray photon energy and is non-invasive, allowing it to be incorporated into any pump–probe experiment, eventually characterizing pulses before and after interaction with most sample environments.

We propose a two-color pump–probe Thomson scattering experiment at the FLASH facility in Hamburg to characterize warm dense matter states. The fundamental free electron laser wavelength of 40.5 nm is used to pump a liquid hydrogen jet that is subsequently probed with the third harmonic at 13.5 nm. We have considered the laser–target interaction in the pump and probe phase by using the radiation hydrodynamics code HELIOS. The calculation of the Thomson scattering spectrum is based on the Chihara formula which is evaluated using the Born–Mermin approximation for the free electron dynamic structure factor and the Debye–Huckel static structure factor for the elastic scattering part. We consider the full density- and temperature-dependent Thomson scattering cross section throughout the inhomogeneous target. The results indicate that the electron–ion equilibration rate can be extracted by measuring the electron and ion feature with varying time delays between the pump and the probe pulse.

International audience

The European X-ray free electron laser source (XFEL) will provide highly brilliant ( B > 10 33 ph/s/mm 2 /mrad 2 /0.1% bw) and coherent X-ray beams. The pulse structure and the unprecedented brightness will allow one for the first time to study fast dynamics in the time domain, thus giving direct access to the dynamic response function S ( Q , t ), instead of S ( Q , ω ), which is of central importance for a variety of phenomena such as fast non-equilibrium dynamics initiated, e.g. by a short pump pulse. X-ray photon correlation spectroscopy (XPCS) measures the temporal changes in speckle patterns produced when coherent light is scattered by a disordered system and therefore allows to measure S ( Q , t ). This paper summarizes important aspects of the scientific case for an XPCS instrument at the planned XFEL. Novel XPCS set-ups are illustrated.

The European X-ray Free-Electron Laser Facility (XFEL) will be the first next-generation light source user facility for hard X-ray research combining extreme peak with very high average brilliance. Five photon beamlines will deliver ultrashort, coherent radiation pulses, generated by superconducting linear accelerator technology and long permanent-magnet undulators to an initial set of ten scientific instruments. Free-electron laser radiation in the photon energy range from 250 eV to 12.4 keV and spontaneous radiation in the range from 20 keV up to a few 100 keV will be provided. Figure 1 shows the selected site for the European XFEL in Hamburg, Germany. The preparation for the European XFEL is supervised by an International Steering Committee including members from 13 partner countries. The start of construction is planned for the first half of 2007 and first beam is scheduled for 2013.

In the next decade the scientific community expects a strong impact in physics, chemistry, biology, material research and life sciences by the availability of high-brilliance X-ray radiation from free-electron laser (FEL) sources. In particular, in the field of ultrafast science these new sources will allow new types of experiments, enabling new phenomena to be discovered. Whereas today ultrafast X-ray diffraction experiments are strongly restricted by the limited X-ray flux of current sources of sub-picosecond X-ray pulses, FELs will provide short pulses of typically 10{sup 12} photons with a duration of the order of 100 fs and monochromaticity of 10{sup -3}. Here, the feasibility of time-resolved single-shot powder diffraction experiments using these intense pulses, and the requirements of these experiments, are discussed. The detector count rates are estimated for diffraction from a model compound in a wide q-regime under the special consideration of high resolving power. In the case of LCLS radiation parameters, single-shot experiments will be feasible although high-resolution powder diffraction will require a reduction of the intrinsic FEL radiation bandwidth.

We have investigated non-resonant high energy X-ray magnetic scattering from EuAs3 both in the antiferromagnetic and in the incommensurate phase by using an X-ray energy of 104 and 106 keV. In the antiferromagnetic phase, we obtained a signal to background ratio of about 10:1 for the magnetic Bragg peak at Q = ( − 1 , 0 , 1 / 2 ) and a maximum count rate of about 200 counts/s at T=3.1 K. To our knowledge this is the first reported observation of the non-resonant magnetic signal from a rare-earth ion at X-ray energy as high as 106 keV. The temperature dependence of the integrated intensity of the (−1,0,1/2); magnetic reflection has been measured and compared with that obtained previously by neutron diffraction. We measured the integrated intensities of several magnetic reflections from the antiferromagnetic phase and have compared them with those calculated from the magnetic structure model derived from neutron diffraction. The intensities of the magnetic satellite reflections from the incommensurate phase have been measured and have been found to be very weak. We also investigated the temperature variation of the lattice spacing close to the magnetic ordering transition and have found a large magnetoelastic anomaly at the lock-in phase transition.

Free-electron laser (FEL) radiation using high energy electron accelerators will enable ultrafast time-resolved X-ray scattering for applications ranging from atomic physics, via plasma and solid-state physics to chemistry and structural biology. The high scientific potential of FELs operated in the self-amplified spontaneous emission (SASE) mode is determined by their radiation characteristics in the wavelength regime from 0.1 to 100 nm. Typically 10 12 –10 13 photons are provided within a single pulse of the order 100 fs duration. The SASE process implies coherent emission and the coherence properties of hard X-ray FEL radiation therefore exceed those of existing X-ray sources by orders of magnitude. Time-resolved experiments using FEL radiation will in many cases allow data collection from single pulses. Statistical fluctuations lead to an enhanced requirement for diagnostics of intensity, spectral and temporal distributions.

Texture measurement with short-wave X-ray synchrotron radiation in the range of λ ≃ 0.1 Å is described. The measurements were carried out with the multipurpose diffraction instrument at the high-field wiggler, high-energy beamline BW5 at HASYLAB. The instrument was equipped with an on-line image-plate area detector for diffraction-image registration and a Eulerian cradle for sample orientation. The particular features of texture measurement with the BW5 instrument are: good resolution in the Bragg angle, extremely high angular resolution in crystal orientation (pole-figure angles) and particularly high penetration depth of several millimetres to centimetres, comparable with that of neutrons but at high spatial resolution. Several examples illustrate the particular advantages of this method for texture studies using large or encased samples (in situstudies in complicated environments, such as cryostats, furnaces, vacuum or pressure chambers, with no serious window problems). This allows, among others, non-destructive texture analysis in technological parts and whole components. Because of the extremely high beam intensity (short exposure times) compared with all other methods of texture measurement, the new technique is particularly suited for the study of large sample series (as is often necessary in industrial applications).

The microstructural dynamics of Bi-2223 tapes are investigated in situ during annealing in 8% O2 by means of 100 keV x-ray diffraction. A green mono- and a green multi-filamentary tape are annealed at 829.5 °C. During ramp-up (Ca,Sr)2PbO4 decomposes above 750 °C, resulting in an incorporation of Pb in Bi-2212. The associated grain growth of Bi-2212 is the main cause of the strain relief and the c-axis grain alignment of the Bi containing phases. Above 825 °C the Bi-2212 partly dissociates into (Ca,Sr)14Cu24Ox and a liquid phase. The linewidth of Bi-2212 is constant during the transformation to Bi-2223, indicating no strain or finite-size broadening. The most probable transformation mechanism is found to be nucleation and growth with a fast decomposition of the individual Bi-2212 grain, followed by a growth of Bi-2223 from the Bi-2212 melt reacting with (Ca,Sr)14Cu24Ox. The multi-filamentary tape transforms faster and exhibits a much better degree of c-axis alignment. Results are compared to similar studies in air. During a final annealing of a fully converted tape no change is found in the average concentration, stoichiometry and grain misalignment. A post-annealing experiment at 650 °C on quenched tapes shows a reaction over 3 weeks, whereby randomly oriented 3222 grains are formed and Bi-2223 is depleted of Pb. Simultaneously, the critical current decreases by a factor of 2.

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.

We report on the dynamics of ultrafast heating in cryogenic hydrogen initiated by a ≲300 fs, 92 eV free electron laser x-ray burst. The rise of the x-ray scattering amplitude from a second x-ray pulse probes the transition from dense cryogenic molecular hydrogen to a nearly uncorrelated plasmalike structure, indicating an electron-ion equilibration time of ∼0.9 ps. The rise time agrees with radiation hydrodynamics simulations based on a conductivity model for partially ionized plasma that is validated by two-temperature density-functional theory. © 2014 American Physical Society.

We report the results of two experiments performed on uranium monosulphide: measuring the magnetic Compton scattering (MCS) and x-ray magnetic circular dichroism (XMCD) at the M4,5 uranium absorption edges. From the MCS experiment we get the spin moment of both the localized (5f electrons) and the diffuse (mainly 6d electrons) contributions. Combining these results with bulk magnetization and published neutron diffraction data, we can separate the orbital and spin contributions to the localized and diffuse moments. Using the XMCD measurements, we deduce the expectation value of the magnetic dipole operator. We finally compare our results on US with published measurements made on USe and UTe.

The design for a combined single crystal and multilayer monochromator for beamline L of HASYLAB, dedicated to X-ray fluorescence detection and microfocus applications, is presented. The high-resolution Si crystal monochromator is designed for use in chemical state-selective experiments in the X-ray absorption near edge structures mode (XANES). Broadband excitation by the multilayer monochromator will enable total reflection X-ray fluorescence (TXRF) experiments and improved detection limits for microfocus X-ray fluorescence analysis in many cases, e.g. for light elements in heavy matrices. An energy range of 2.4–80 keV shall be explored by the instrument, giving access to the K-edges of elements with 16⩽ Z ⩽79.

An instrument for diffraction texture measurements in polycrystalline bulk materials using hard X-ray photons from the wiggler beamline BW5 at HASYLAB is described. High-energy photons in the 100 keV regime enable high penetration power in medium-to-high Z materials and the use of Laue diffraction geometry in combination with a two-dimensional area detector allows fast and convenient data collection. Determination of quantitative, high-resolution pole figures with a better angular resolution of 0.1° is attained by the instrument. Profile analysis of the diffraction pattern parameters for each ( h k l )-reflection thus provides, in addition to texture data, information about other microstructural quantities, e.g. lattice strain.

A new X-ray optical system for the fluorescence beamline L at HASYLAB is currently under construction and its commissioning phase will start early in 2001. Basis elements of the optical system are a double single-crystal - double multilayer monochromator, X-ray mirrors and capillary optics. The high-resolution Si crystal monochromator is designed for microscopic X-ray absorption near-edge structures (μ-XANES) experiments in fluorescence mode for laterally resolved speciation of trace elements. Broadband excitation by the multilayer monochromator will be used in total reflection X-ray fluorescence (TXRF) experiments and microscopic X-ray fluorescence analysis (μ-XRF). An energy range of 2.4-80 keV will be explored by the monochromator system, giving access to the K-edges of elements with 16 < Z < 79. A set of plane and cylindrical X-ray mirrors allows a high-energy cut-off at 12 and 30 keV, respectively and optional prefocusing. The microfocus is generated by monocapillaries and polycapillaries. The performance of different monocapillary optics in the synchrotron beam was measured in polychromatic and monochromatic modes.

We have studied the electron-momentum density distribution in Al using the coincidence as well as the conventional high-resolution Compton scattering technique. In order to interpret the results, corresponding band theory based computations of the electron momentum density (EMD) and the Compton profiles (CPs) have been carried out. Our focus here is on determining the size of the break ZF in the EMD at the Fermi momentum. For this purpose, differences between measurements and theoretical predictions are analyzed in terms of a simple model for describing electron correlation effects which are missing from the independent particle band theory framework; the model involves ZF as the only adjustable parameter. A good fit with the coincidence measurements is obtained for ZF of about 0.7, while the CP data yields ZF=0.7 to 0.8. This study suggests that, in sharp contrast to the case of Li where recent high-resolution Compton work indicates ZF≈0, the standard picture of the interacting electron gas is substantially correct in Al.

Physical review / B 60(20), 14049 - 14056 (1999). doi:10.1103/PhysRevB.60.14049, We report on the measurement of the three-dimensional electron momentum density (EMD) of a 22 nm Cu/22 nm Ni sandwich foil and of a Cu0.50Ni0.50 alloy film with the same thickness, which was obtained from an identical sandwich by interdiffusion. The EMD’s were measured by coincident detection of a Compton scattered photon with its recoil electron. The experiments were performed at the High-Energy beamline of the European Synchrotron Radiation Facility. The experimentally observed small change of the EMD due to alloying is reproduced by the Korringa-Kohn-Rostoker coherent-potential approximation scheme [Benedek et al., Phys. Rev. B 32, 7650 (1985)]., Published by Inst., Woodbury, NY

Element-sensitive tomography produces quality information in the field of medical imaging. This method, also known as dichromatic tomography, can be useful to visualize the distribution of heavy elements, such as actinides, without destroying the sample. One of the problems is to obtain a monochromatic photon beam of sufficiently high energy; the other is to have a way of recording these high-energy photons with a good spatial resolution. Here, the results of a first experiment on uranium mapping with synchrotron radiation are reported. Various natural and artificial samples of a few centimetres in size with uranium concentration between 0.008 g cm−3 and 2 g cm−3 were scanned using photon beams around 115 keV and a specially designed camera. The data were then analysed using a conventional fast reconstruction technique. This yielded excellent results with spatial resolutions down to 50 µm. For the first time it was shown that element-sensitive tomography using synchrotron radiation could be extended to the heaviest natural element. Therefore, in principle, the spatial distribution of any element can now be reconstructed using synchrotron radiation. Extension of this technique to very heavy elements can be important for geology, health physics and nuclear waste storage.

We report on the measurement of the three-dimensional electron momentum density (EMD) of aluminum. 150 keV photons with an intensity of $2\ifmmode\times\else\texttimes\fi{}{10}^{11}$ photons/s from a multipole wiggler of the European Synchrotron Radiation Facility have been scattered at a 100 nm thin self-supporting aluminum foil and measured in coincidence with their recoil electrons. To improve the agreement with a full potential linear muffin-tin orbital theory, electron correlation effects have been incorporated via the so-called Lam-Platzman correction [Phys. Rev. B 9, 5122 (1974)]. A comparison with two-dimensional angular correlation of annihilation radiation has been made and demonstrates the strong influence of the positron wave function on the EMD. In analogy to these experiments, we used the first derivative of the EMD as an indication of the Fermi breaks.

A scanning-type crystal spectrometer for high-resolution Compton profile measurements has been constructed at the High Energy Inelastic Scattering Beamline (ID15B) of the ESRF. Radiation from a seven-period asymmetrical permanent-magnet wiggler or from a superconducting wavelength shifter is focused horizontally onto the sample by a bent-crystal monochromator. Typical energies are 30, 50 and 60 keV, the flux on the sample is 1012 photons s−1, and the relative energy bandwidth is 3 × 10−4. The spectrometer operates in the Rowland circle geometry, where the sample is fixed and the cylindrically bent analyser crystal and the detector move on the focusing circle by synchronized translations and rotations. The main detector is a large-diameter NaI scintillation counter, the incident beam is monitored by an Si diode, and scattering from the sample is detected using a Ge detector. The recorded spectrum is corrected for the energy-dependent response of the spectrometer, background and multiple scattering, and converted to the momentum scale. The resolution of the spectrometer is calculated from the geometrical factors and the reflectivity curve of the analyser crystal, and the result is checked against the widths of the elastically scattered line and fluorescent lines. So far, 0.1 a.u. resolution in electron momentum has been achieved. The typical average count rate over the Compton profile is about 1000 counts s−1 from a weakly absorbing sample.

We report on the three-dimensional electron momentum densities (EMD) of graphite and fullerene obtained by a so-called (,e) experiment, i.e. the coincident detection of an inelastically scattered hard x-ray photon with its recoil electron. A monochromatized flux of 1012 photons s-1 at 150 keV from the high-energy x-ray wiggler beamline of the ESRF was directed onto thin graphite or fullerene targets. Comparison with a pseudopotential and a full-potential linear muffin-tin orbital calculation in the case of graphite is made. Inclusion of electron correlation via the Lam-Platzman correction is discussed. The experimental EMD of C60 shows stronger electron delocalization in the `buckyball' compared to graphite, which is supported by theory.

High energy synchrotron diffraction is introduced as a new method for residual stress analysis in the bulk of materials. It is shown that energy dispersive measurements are sufficiently precise so that strains as small 10−4 can be determined reliably. Due to the high intensity and the high parallelism of the high energy synchrotron radiation the sample gauge volume can be reduced to approximately 50 μm×1 mm×1 mm compared to gauge volume of one mm3 up to several mm3 achievable by neutron diffraction. The benefits of the high penetration depth and the small gauge volume are demonstrated by the results of stress studies performed on a fiber reinforced ceramic, a functional gradient material and a metal-ceramic compound. Furthermore, it is shown that in case of a cold extruded metal specimen the energy dispersive measurement technique yields simultaneous information about texture and residual stresses and thus allows a detailed investigation of elastic and plastic deformation gradients.

We report a high-energy magnetic-Compton-scattering study performed on the ferromagnet CeRh{sub 3}B{sub 2}. This technique solely measures the electron spin magnetic moments. In contrast to a number of Ce intermetallics with nonmagnetic elements, the Ce 5d spin moment is found to be large and parallel to the Ce 4f spin moment. Therefore the Kondo effect does not play a key role for CeRh{sub 3}B{sub 2}. The inferred large Ce 5d orbital magnetic moment is a signature of the strong spin-orbit interaction for the Ce 5d band. {copyright} {ital 1998} {ital The American Physical Society}

Results of high-energy magnetic X-ray diraction for photon energies up to 500 keV are presented and the form of the magnetic scattering cross-section for relativistic energies is discussed. At 300 keV we experimentally proved that the scattering from the spin component perpendicular to the scattering plane is dominant. Within our statistical and systematic errors, the magnetic scattering amplitude for this component does not exhibit any variation with energy between 100 and 500 keV. Introduction. { Magnetic X-ray diraction with high-energy photons exhibits certain advantages with respect to neutron and medium-energy X-ray diraction which are discussed in detail in (1), (2). These include true bulk sensitivity, volume-enhancement of the magnetic signal, high momentum space resolution and a simple form of the magnetic scattering cross- section. For this reason, magnetic scattering with hard X-rays at an energy of 80 keV has been developed during the last years (1), (2). At this energy, the rst-order approximation in h!=mc 2 for the magnetic scattering amplitude is valid in very good approximation. For magnetic diraction at higher energies, when the photon energy approaches the electron rest mass mc 2 = 511 keV, a complete quantum-relativistic treatment is necessary, taking into account all eects arising from the coupling of the quantized photon eld and the Dirac eld of the electrons. To our knowledge, a corresponding theory is missing. To investigate experimentally how the scattering cross-section behaves for higher photon energies, we measured magnetic Bragg reflections of MnF2 at energies up to 500 keV. Magnetic scattering cross-section for hard X-rays. { A calculation of the cross-section for X-ray scattering including the magnetic terms from a quasi-relativistic Hamiltonian for

By the coincidental detection of an inelastically scattered hard X-ray photon and its recoil electron (i.e. a so-called (γ,eγ) experiment) cuts through the 3D-electron momentum density (EMD) of graphite have been measured and are compared with a theoretical EMD based on a pseudopotential calculation. Peak shifts of the EMD as a function of the electron emission angle are discussed by a detailed consideration of the scattering kinematics. Experiments have been performed at the European Synchrotron Radiation Facility (ESRF) at Grenoble, France.

Short-wavelength free-electron lasers are now well established as essential and unrivalled sources of ultrabright coherent X-ray radiation. One of the key characteristics of these intense X-ray pulses is their expected few-femtosecond duration. No measurement has succeeded so far in directly determining the temporal structure or even the duration of these ultrashort pulses in the few-femtosecond range. Here, by deploying the so-called streaking spectroscopy technique at the Linac Coherent Light Source, we demonstrate a non-invasive scheme for temporal characterization of X-ray pulses with sub-femtosecond resolution. This method is independent of photon energy, decoupled from machine parameters, and provides an upper bound on the X-ray pulse duration. We measured the duration of the shortest X-ray pulses currently available to be on average no longer than 4.4 fs. Analysing the pulse substructure indicates a small percentage of the free-electron laser pulses consisting of individual high-intensity spikes to be on the order of hundreds of attoseconds. Using a spectroscopy streaking technique at LCLS (Linac Coherent Light Source), researchers demonstrate temporal characterization of X-ray pulses with sub-femtosecond resolution.

The complete 3D-electron momentum density (EMD) of solids can be measured by the coincident detection of an inelastically scattered hard X-ray photon and its recoil electron (i.e. a so-called (γ,eγ) experiment). To avoid multiple scattering of the recoil electron the experiment has been performed with a 22 nm thin graphite foil made by laser plasma ablation. The experimental EMD is compared with a pseudopotential calculation. Experiments have been made both at the European Synchrotron Radiation Facility at Grenoble, France, and at the PETRA storage ring of DESY, Hamburg, Germany.

Results of high-energy non-resonant magnetic X-ray diffraction experiments performed on the model system MnF 2 at a photon energy of 80keV are presented. A surprisingly high peak intensity of the magnetic 300 reflection of 13 000 photonss -1 in the three-crystal mode and 19 000 photons s -1 in the two-crystal mode, with a peak-to-background ratio of 230 :1 and 10 :1, respectively, has been achieved. At 80keV, the penetration depth is 7mm. When the path length of the beam through the crystal is varied, the effect of volume enhancement of the intensity diffracted by magnetic reflections is demonstrated. The Q dependence of the magnetic and the charge Bragg reflections has been measured and agrees well with theory. The measurement of the temperature dependence of the sublattice magnetization allows a very accurate determination of the critical exponent β = 0.333 (3) and the Neel temperature T N = 67.713 (2) K. Finally, the multiple charge scattering is discussed, which is very pronounced for the magnetic reflections of MnF 2 .

The combination of powerful optical lasers and an x-ray free-electron laser (XFEL) provides unique capabilities to study the transient behaviour of matter in extreme conditions. The high energy density science instrument (HED instrument) at the European XFEL will provide the experimental platform on which an unique x-ray source can be combined with various types of high-power optical lasers. In this paper, we highlight selected scientific examples together with the associated x-ray techniques, with particular emphasis on femtosecond (fs)-timescale pump–probe experiments. Subsequently, we present the current design status of the HED instrument, outlining how the experiments could be performed. First user experiments will start at the beginning of 2018, after which various optical lasers will be commissioned and made available to the international scientific community.

The scientific background and scope of research at the High Energy Scattering Beamlines of the European Synchrotron Radiation Facility are reviewed briefly. The beamline has two different insertion devices (IDs), a permanent magnet multipole wiggler and a superconducting wavelength shifter. The IDs can be used alternatingly, and both provide circularly polarized radiation off the orbit plane up to energies of several hundreds of keV. Measurements of the spectral brightness and the polarization components by energy dispersive powder diffraction and Compton scattering from iron in an alternating magnetic field are presented and compared with calculations based on source parameters. The beamline optics are based on use of horizontally reflecting bent Si crystals. These provide various focusing geometries, and the calculated flux of monochromatic radiation is given at energies between 30 and 175 keV. The maximum of 2×1012 photons/s is reached at 80 keV. The main experimental apparatus in the initial operation includes a high‐resolution three‐axis diffractometer, and a scanning‐type Compton spectrometer.

A common misperception of quantum gravity is that it requires accessing energies up to the Planck scale of 1019GeV, which is unattainable from any conceivable particle collider. Thanks to the development of ultra-high intensity optical lasers, very large accelerations can be now the reached at their focal spot, thus mimicking, by virtue of the equivalence principle, a non Minkowski space-time. Here we derive a semiclassical extension of quantum mechanics that applies to different metrics, but under the assumption of weak gravity. We use our results to show that Thomson scattering of photons by uniformly accelerated electrons predicts an observable effect depending upon acceleration and local metric. In the laboratory frame, a broadening of the Thomson scattered x ray light from a fourth generation light source can be used to detect the modification of the metric associated to electrons accelerated in the field of a high power optical laser.

Two-color ($\mathrm{x}\mathrm{\text{\ensuremath{-}}}\mathrm{ray}+\mathrm{\text{infrared}}$) electron spectroscopy is used for investigating laser-assisted $KLL$ Auger decay following $1s$ photoionization of atomic Ne with few-femtosecond x-ray pulses from the Linac Coherent Light Source. In an angle-resolved experiment, the overall width of the laser-modified Auger-electron spectrum and its structure change significantly as a function of the emission angle. The spectra are characterized by a strong intensity variation of the sidebands revealing a gross structure. This variation is caused, as predicted by theory, by the interference of electrons emitted at different times within the duration of one optical cycle of the infrared dressing laser, which almost coincides with the lifetime of the Ne $1s$ vacancy.

We present the results of an experiment where amorphous carbon undergoes a phase transition induced by femtosecond 830 eV x-ray free-electron laser pulses. The phase transition threshold fluence is found to be 282 +/- 11 mJ/cm(2). Atomic force microscopy, photoelectron microscopy, and micro-Raman spectroscopy give experimental evidence for the phase transition in terms of a volume expansion, graphitization, and change of local order of the irradiated sample area. The interaction is modeled by an accurate time-dependent treatment of the ionization dynamics coupled to a two-temperature model. At the phase transition fluence threshold the free-electron density N-e is found to be at maximum 9 x 10(20) cm(-3) while the ion (atom) temperature is found to be 1050 K, e.g., above the crystallization activation temperature reported in the literature. This low ionization rate and high atom temperature suggest a thermally activated phase transition.

We present results of a time-resolved pump-probe experiment where a Si sample was exposed to an intense 15 keV beam and its surface monitored by measuring the wavefront deformation of a reflected optical laser probe beam. By reconstructing and back propagating the wavefront, the deformed surface can be retrieved for each time step. The dynamics of the heat bump, build-up and relaxation, is followed with a spatial resolution in the nanometer range. The results are interpreted taking into account results of finite element method simulations. Due to its robustness and simplicity this method should find further developments at new x-ray light sources (FEL) or be used to gain understanding on thermo-dynamical behavior of highly excited materials. (C) 2011 Optical Society of America

The European XFEL is a hard x-ray Free-Electron Laser currently under construction in Hamburg. This international facility will deliver in 2015 femtosecond pulses of soft to hard x-ray light. In this article, we present the main characteristics of the facility and give a brief overview of the foreseen science to be adressed. An emphasize will be given on the beamline design. In fact x-ray FEL beam present specific and completely new characteristics which require the development of new technical solution. The on-going effort to tackle all the relevant challenges is presented, as well an overview of the conceptual design for the different European XFEL beamlines.

We report coincidence measurements of inelastically scattered 148 keV photons and the recoil electrons generated within thin Al and Cu foils. We have analyzed both the Doppler broadening of the scattered photon intensity and the angular correlation of the recoil electron. This corresponds to different scans through the three-dimensional electron momentum density of the target. Estimates of the triple-differential cross-section for Compton scattering are given. The experiment was performed with synchrotron radiation from a bending magnet of the DORIS storage ring at DESY, Hamburg.

International audience; X-ray scattering using highly brilliant X-ray free-electron laser (FEL) radiation provides a new access to probe free electron density, temperature and ionization in near-solid density plasmas. First experiments at the soft X-ray FEL FLASH at DESY, Hamburg, show the capabilities of this technique. The ultrashort FEL pulses in particular can probe equilibration phenomena occurring after excitation of the plasma using ultrashort optical laser pumping. We have investigated liquid hydrogen and find that the interaction of very intense soft X-ray FEL radiation alone heats the sample volume. As the plasma establishes, photons from the same pulse undergo scattering, thus probing the transient, warm dense matter state. We find a free electron density of (2.6 ± 0.2) · 10 20 cm −3 and an electron temperature of 14 ± 3.5 eV. In pump-probe experiments, using intense optical laser pulses to generate more extreme states of matter, this interaction of the probe pulse has to be considered in the interpretation of scattering data. In this paper we present details of the experimental setup at FLASH and the diagnostic methods used to quantitatively analyze the data. Probing near-solid density plasmas using soft X-ray scattering 2 Plasma production and heating by laser beams Probing near-solid density plasmas using soft X-ray scattering 3

We investigate ultrafast (fs) electron dynamics in a liquid hydrogen sample, isochorically and volumetrically heated to a moderately coupled plasma state. Thomson scattering measurements using 91.8 eV photons from the free-electron laser in Hamburg (FLASH at DESY) show that the hydrogen plasma has been driven to a nonthermal state with an electron temperature of 13 eV and an ion temperature below 0.1 eV, while the free-electron density is 2.8x10{20} cm{-3}. For dense plasmas, our experimental data strongly support a nonequilibrium kinetics model that uses impact ionization cross sections based on classical free-electron collisions.

The introduction of brilliant free-electron lasers enables new pump-probe experiments to characterize warm dense matter states. For instance, a short-pulse optical laser irradiates a liquid hydrogen jet that is subsequently probed with brilliant soft x-ray radiation. The strongly inhomogeneous plasma prepared by the optical laser is characterized with particle-in-cell simulations. The interaction of the soft x-ray probe radiation for different time delays between pump and probe with the inhomogeneous plasma is also taken into account via radiative hydrodynamic simulations. We calculate the respective scattering spectrum based on the Born-Mermin approximation for the dynamic structure factor considering the full density and temperature-dependent Thomson scattering cross section throughout the target. We can identify plasmon modes that are generated in different target regions and monitor their temporal evolution. Therefore, such pump-probe experiments are promising tools not only to measure the important plasma parameters density and temperature but also to gain valuable information about their time-dependent profile through the target. The method described here can be applied to various pump-probe scenarios by combining optical lasers and soft x ray, as well as x-ray sources.

A compact and light weight soft X-ray spectrograph covering 5−35 nm and employing a toroidal mirror and a variable line space reflection grating has been newly developed. Particular emphasis has been placed on achieving a large collection solid angle (1.9 × 10−3 sr) and a high efficiency of the components in order to enable Thomson Scattering plasma diagnostics which has a small total cross section (6.65 × 10−25 cm2). The instrument achieves a signal-to-noise ratio of 5 with a 13.5 nm source which isotropically emits 2.5 × 105 photons. A resolution λ/Δλ = 330 was measured at 21 nm and the dispersion was calibrated. The instrument is housed inside a DN 100 CF ultra high vacuum manipulator (43 × 46 × 47 cm3) which allows positioning relative to the source within ±5 mm and ±50 mm in X,Y and Z direction, respectively. It can be used with or without entrance pinhole and is equipped with a motorized grating, a filter wheel with five filters, and a shutter. Altogether, these features make the spectrograph a versatile instrument which can be employed in a variety of physics applications such as line and bremsstrahlung spectroscopy or Thomson scattering.

We report on the performance of a 60 kHz repetition rate sub-10 fs, optical parametric chirped pulse amplifier system with 2 W average power and 3 GW peak power. This is to our knowledge the highest average power sub-10 fs kHz-amplifier system reported to date. The amplifier is conceived for applications at free electron laser facilities and is designed such to be scalable in energy and repetition rate.

In this Letter, we report the pioneering use of free electron laser radiation for the investigation of periodic crystalline structures. The diffraction properties of silver behenate single nanocrystals (5.8 nm periodicity) with the dimensions of $20\text{ }\text{ }\mathrm{nm}\ifmmode\times\else\texttimes\fi{}20\text{ }\text{ }\mathrm{nm}\ifmmode\times\else\texttimes\fi{}20\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ and as powder with grain sizes smaller than 200 nm were investigated with 8 nm free electron laser radiation in single-shot modus with 30 fs long free electron laser pulses. This work emphasizes the possibility of using soft x-ray free electron laser radiation for these crystallographic studies on a nanometer scale.

The European x-ray free-electron laser (XFEL) provides x-ray self-amplified spontaneous emission (SASE) FEL radiation in the wavelength range from 0.1 to 3 nm using three undulator systems. The SASE mode of operation at the European XFEL defines specific behavior of longitudinal and transverse coherence properties. In this paper, we describe the evolution of the temporal and transverse correlation functions along the undulator length, and we extract the corresponding evolution of coherence time and degree of transverse coherence as typical figures of merit. Generation of coherent radiation inside the FEL undulators is followed by beam transport to the experiments. During transport, the total number of coherent modes is preserved, but the wavefront can be disturbed, and we analyze the conditions under which this occurs. It is emphasized that the development of experimental observables for the degree of coherence and wavefront properties will be important for experiments using coherent x-ray radiation.