(Sub-)Picosecond Surface Correlations of Femtosecond Laser Excited Al-Coated Multilayers Observed by Grazing-Incidence X-ray Scattering.

Femtosecond high-intensity laser pulses at intensities surpassing 10 W/cm can generate a diverse range of functional surface nanostructures. Achieving precise control over the production of these functional structures necessitates a thorough understanding of the surface morphology dynamics with nanometer-scale spatial resolution and picosecond-scale temporal resolution. In this study, we show that single XFEL pulses can elucidate structural changes on surfaces induced by laser-generated plasmas using grazing-incidence small-angle X-ray scattering (GISAXS).

Damage threshold of LiF crystal irradiated by femtosecond hard XFEL pulse sequence.

Here we demonstrate the results of investigating the damage threshold of a LiF crystal after irradiating it with a sequence of coherent femtosecond pulses using the European X-ray Free Electron Laser (EuXFEL). The laser fluxes on the crystal surface varied in the range ∼ 0.015-13 kJ/cm per pulse when irradiated with a sequence of 1-100 pulses (t ∼ 20 fs, E = 9 keV).

Hard X-ray stereographic microscopy for single-shot differential phase imaging.

The characterisation of fast phenomena at the microscopic scale is required for the understanding of catastrophic responses of materials to loads and shocks, the processing of materials by optical or mechanical means, the processes involved in many key technologies such as additive manufacturing and microfluidics, and the mixing of fuels in combustion. Such processes are usually stochastic in nature and occur within the opaque interior volumes of materials or samples, with complex dynamics that evolve in all three dimensions at speeds exceeding many meters per second. There is therefore a need for the ability to record three-dimensional X-ray movies of irreversible processes with resolutions of micrometers and frame rates of microseconds.

Direct LiF imaging diagnostics on refractive X-ray focusing at the EuXFEL High Energy Density instrument.

The application of fluorescent crystal media in wide-range X-ray detectors provides an opportunity to directly image the spatial distribution of ultra-intense X-ray beams including investigation of the focal spot of free-electron lasers. Here the capabilities of the micro- and nano-focusing X-ray refractive optics available at the High Energy Density instrument of the European XFEL are reported, as measured in situ by means of a LiF fluorescent detector placed into and around the beam caustic. The intensity distribution of the beam focused down to several hundred nanometers was imaged at 9 keV photon energy.

Spectral monitoring at SwissFEL using a high-resolution on-line hard X-ray single-shot spectrometer.

The performance and parameters of the online photon single-shot spectrometer (PSSS) at the Aramis beamline of the SwissFEL free-electron laser are presented. The device operates between the photon energies 4 and 13 keV and uses diamond transmission gratings and bent Si crystals for spectral measurements on the first diffraction order of the beam. The device has an energy window of 0.

The High Energy Density Scientific Instrument at the European XFEL.

The European XFEL delivers up to 27000 intense (>10 photons) pulses per second, of ultrashort (≤50 fs) and transversely coherent X-ray radiation, at a maximum repetition rate of 4.5 MHz. Its unique X-ray beam parameters enable groundbreaking experiments in matter at extreme conditions at the High Energy Density (HED) scientific instrument.

X-ray Free Electron Laser-Induced Synthesis of ε-Iron Nitride at High Pressures.

The ultrafast synthesis of ε-FeN in a diamond-anvil cell (DAC) from Fe and N under pressure was observed using serial exposures of an X-ray free electron laser (XFEL). When the sample at 5 GPa was irradiated by a pulse train separated by 443 ns, the estimated sample temperature at the delay time was above 1400 K, confirmed by transformation of α- to γ-iron. Ultimately, the Fe and N reacted uniformly throughout the beam path to form FeN, as deduced from its established equation of state (EOS).

Wavefront sensing at X-ray free-electron lasers.

Here a direct comparison is made between various X-ray wavefront sensing methods with application to optics alignment and focus characterization at X-ray free-electron lasers (XFELs). Focus optimization at XFEL beamlines presents unique challenges due to high peak powers as well as beam pointing instability, meaning that techniques capable of single-shot measurement and that probe the wavefront at an out-of-focus location are desirable. The techniques chosen for the comparison include single-phase-grating Talbot interferometry (shearing interferometry), dual-grating Talbot interferometry (moiré deflectometry) and speckle tracking.

SwissFEL Aramis beamline photon diagnostics. Erratum.

The list of authors in the paper by Juranić et al. (2018) [J. Synchrotron Rad.

Characterizing transmissive diamond gratings as beam splitters for the hard X-ray single-shot spectrometer of the European XFEL.

The European X-ray Free Electron Laser (EuXFEL) offers intense, coherent femtosecond pulses, resulting in characteristic peak brilliance values a billion times higher than that of conventional synchrotron facilities. Such pulses result in extreme peak radiation levels of the order of terawatts cm for any optical component in the beam and can exceed the ablation threshold of many materials. Diamond is considered the optimal material for such applications due to its high thermal conductivity (2052 W mK at 300 K) and low absorption for hard X-rays.

Initial observations of the femtosecond timing jitter at the European XFEL.

Intense, ultrashort, and high-repetition-rate X-ray pulses, combined with a femtosecond optical laser, allow pump-probe experiments with fast data acquisition and femtosecond time resolution. However, the relative timing of the X-ray pulses and the optical laser pulses can be controlled only to a level of the intrinsic error of the instrument which, without characterization, limits the time resolution of experiments. This limitation inevitably calls for a precise determination of the relative arrival time, which can be used after measurement for sorting and tagging the experimental data to a much finer resolution than it can be controlled to.

Demonstration of femtosecond X-ray pump X-ray probe diffraction on protein crystals.

The development of X-ray free-electron lasers (XFELs) has opened the possibility to investigate the ultrafast dynamics of biomacromolecules using X-ray diffraction. Whereas an increasing number of structures solved by means of serial femtosecond crystallography at XFELs is available, the effect of radiation damage on protein crystals during ultrafast exposures has remained an open question. We used a split-and-delay line based on diffractive X-ray optics at the Linac Coherent Light Source XFEL to investigate the time dependence of X-ray radiation damage to lysozyme crystals.

SwissFEL Aramis beamline photon diagnostics.

The SwissFEL Aramis beamline, covering the photon energies between 1.77 keV and 12.7 keV, features a suite of online photon diagnostics tools to help both users and FEL operators in analysing data and optimizing experimental and beamline performance.

Single-shot Monitoring of Ultrafast Processes via X-ray Streaking at a Free Electron Laser.

The advent of x-ray free electron lasers has extended the unique capabilities of resonant x-ray spectroscopy techniques to ultrafast time scales. Here, we report on a novel experimental method that allows retrieving with a single x-ray pulse the time evolution of an ultrafast process, not only at a few discrete time delays, but continuously over an extended time window. We used a single x-ray pulse to resolve the laser-induced ultrafast demagnetisation dynamics in a thin cobalt film over a time window of about 1.

On spectral and temporal coherence of x-ray free-electron laser beams.

A model for the coherence properties of free-electron lasers (FELs) in time and frequency domains is introduced within the framework of classical second-order coherence theory of nonstationary light. An iterative phase-retrieval algorithm is applied to construct an ensemble of field realizations in both domains, based on single-pulse spectra measured at the Linac Coherent Light Source (LCLS) in self-amplified spontaneous emission mode. Such an ensemble describes the specific FEL pulse train in a statistically averaged sense.

Dynamic X-ray diffraction observation of shocked solid iron up to 170 GPa.

Investigation of the iron phase diagram under high pressure and temperature is crucial for the determination of the composition of the cores of rocky planets and for better understanding the generation of planetary magnetic fields. Here we present X-ray diffraction results from laser-driven shock-compressed single-crystal and polycrystalline iron, indicating the presence of solid hexagonal close-packed iron up to pressure of at least 170 GPa along the principal Hugoniot, corresponding to a temperature of 4,150 K. This is confirmed by the agreement between the pressure obtained from the measurement of the iron volume in the sample and the inferred shock strength from velocimetry deductions.