Liquid polymorphism is an intriguing phenomenon that has been found in a few single-component systems, the most famous being water. By supercooling liquid Te to more than 130 K below its melting point and performing simultaneous small-angle and wide-angle X-ray scattering measurements, we observe clear maxima in its thermodynamic response functions around 615 K, suggesting the possible existence of liquid polymorphism. A close look at the underlying structural evolution shows the development of intermediate-range order upon cooling, most strongly around the thermodynamic maxima, which we attribute to bond-orientational ordering. The striking similarities between our results and those of water, despite the lack of hydrogen-bonding and tetrahedrality in Te, indicate that water-like anomalies may be a general phenomenon among liquid systems with competing bond- and density-ordering. Copyright © 2022 the Author(s). Published by PNAS. This article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND).

In this work we report on an ultrashort pulsed laser annealing-driven devitrification of thin film Cu67Zr33 metallic glass characterized by micro-beam X-ray diffraction and electron microscopy techniques. The essential feature of ultrashort pulsed laser annealing is ultrafast heating (1014 K/s) by femtosecond optical excitation followed by extremely rapid cooling (1010–12 K/s) due to heat dissipation into the film substrate. During repetitive optical excitation, we take X-ray diffraction snapshots of the intermediate, frozen-in stages of the glass-crystal transformation to study its kinetics. A quantitative analysis of the diffraction patterns supported by electron microscopy result shows that the glass-crystal transformation proceeds by a rapid formation of an energetically favourable layer of crystalline ZrO2 on the free surface of the glassy film accompanied by nucleation and growth of fcc-Cu in the residual amorphous matrix. We demonstrate that at low effective annealing temperatures the devitrification kinetics of both products is correlated, while at high temperatures they decouple and ZrO2 forms an order of magnitude faster than Cu. © 2021 The Authors

Time-dependent and constituent-specific spectral changes in soft near-edge x-ray absorption spectroscopy (XAS) of an metal/insulator heterostructure after laser excitation are analyzed at the O K-edge with picosecond time resolution. The oxygen absorption edge of the insulator features a uniform intensity decrease of the fine structure at elevated phononic temperatures, which can be quantified by a simple simulation and fitting procedure presented here. Combining XAS with ultrafast electron diffraction measurements and ab initio calculations demonstrates that the transient intensity changes in XAS can be assigned to a transient lattice temperature. Thus, the sensitivity of transient near-edge XAS to phonons is demonstrated. © 2021 American Physical Society

We studied the formation and attenuation of GHz elastic waves in free-standing nanoporous gold films by MeV ultrafast electron diffraction and finite element simulations. By tracing the evolution of the high frequency acoustic waves in time domain, we found that the bicontinuous nanoporous structure in nanoporous gold films results in three-dimensionally acoustic response with low coherence, leading to fast attenuation of the elastic waves in comparison with solid gold films. The morphologically dominated dynamics indicates the nanoporosity plays an important role in the high-frequency acoustic energy relaxation, which shines a light on the applications of dealloyed nanoporous materials in nanodevices and sensors as GHz and THz acoustic filters and dampers. © 2021 Author(s).

Ion beams with energies in the keV regime are widely utilized in solid-state physics, but the ultrafast dynamics triggered by an ion impact onto a solid surface is to date exclusively accessible via simulations based on many untested assumptions and model parameters. A possible experimental access rests on the availability of a laser-synchronized ion source delivering sufficiently short ion pulses for time resolved pump-probe experiments. Here, we demonstrate a new miniaturized ion optical bunching setup for the creation of rare gas ion pulses using strong-field femtosecond laser photoionization. Neutral Ar gas atoms at room temperature are intercepted by a 50 fs, 800 nm laser pulse focused to ∼10 μm spot size. We demonstrate the generation of monoenergetic 2 keV Ar+ ion pulses with 180 ps duration (FWHM) at laser peak intensities around 1014 W cm−2 and of multiply charged Arq+ ions (q = 1-5) at higher laser intensities. The results are in good agreement with detailed ion trajectory simulations, which show that the temporal resolution is essentially limited by the initial (thermal) velocity spread of the generated photo-ions, indicating the possibility to achieve even better time resolution by cooling the gas prior to ionization. © 2021 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft

The transient acoustic response of a free-standing, polycrystalline thin Au-film upon femtosecond optical excitation has been studied by time-resolved Debye-Scherrer x-ray diffraction using ultrashort Cu Kα x-ray pulses from a laser-driven plasma x-ray source. The temporal strain evolution has been determined from the transient shifts of multiple Bragg diffraction peaks. The experimental data are in good agreement with the results of calculations based on the two-temperature model and an acoustic model assuming uniaxial strain propagation in the laser-excited thin film. © 2020 Author(s).

We present a setup for time-resolved X-ray diffraction based on a short pulse, laser-driven plasma X-ray source. The employed modular design provides high flexibility to adapt the setup to the specific requirements (e.g., X-ray optics and sample environment) of particular applications. The configuration discussed here has been optimized toward high angular/momentum resolution and uses Kα-radiation (4.51 keV) from a Ti wire-target in combination with a toroidally bent crystal for collection, monochromatization, and focusing of the emitted radiation. 2 × 10 5 Ti-Kα1 photons per pulse with 10 - 4 relative bandwidth are delivered to the sample at a repetition rate of 10 Hz. This allows for the high dynamic range (104) measurements of transient changes in the rocking curves of materials as for example induced by laser-triggered strain waves. © 2020 Author(s).

Femtosecond laser excitation of solid-state systems creates out-of-equilibrium hot electrons that cool down by transferring their energy to other degrees of freedom and ultimately to lattice vibrations of the solid. By combining ab initio calculations with ultrafast diffuse electron scattering, we gain a detailed understanding of the complex nonequilibrium energy transfer between electrons and phonons in laser-excited Ni metal. Our experimental results show that the wave-vector-resolved population dynamics of phonon modes is distinctly different throughout the Brillouin zone and are in remarkable agreement with our theoretical results. We find that zone-boundary phonon modes become occupied first. As soon as the energy in these modes becomes larger than the average electron energy, a backflow of energy from lattice to electronic degrees of freedom occurs. Subsequent excitation of lower-energy phonon modes drives the thermalization of the whole system on the picosecond time scale. We determine the evolving nonequilibrium phonon occupations, which we find to deviate markedly from thermal occupations. © 2020 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/" Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by "https://www.kb.se/samverkan-och-utveckling/oppen-Tillgang-och-bibsamkonsortiet/bibsamkonsortiet.html" Bibsam.

The impact of an energetic particle onto a solid surface generates a strongly perturbed and extremely localized non-equilibrium state, which relaxes on extremely fast time scales. In order to facilitate a time-resolved observation of the relaxation dynamics using established ultrafast pump-probe techniques, it is necessary to pinpoint the projectile impact in time with sufficient accuracy. In this paper, we propose a concept to generate ultrashort ion pulses via femtosecond photoionization of rare gas atoms entrained in a supersonic jet, combined with ion optical bunching of the resulting ion package. We calculate the photoion cloud generated by an intense focused laser pulse and show that Arq+ ions with q = 1-5 can be generated with a standard table-top laser system, which are then accelerated to energies in the keV range over a very short distance and bunched to impinge onto the target surface in a time-focused manner. Detailed ion trajectory simulations show that single ion pulses of sub-picosecond duration can be generated this way. The influence of space charge broadening is included in the simulations, which reveal that flight time broadening is insignificant for pulses containing up to 10-20 ions and starts to increase the pulse width above ∼50 ions/pulse. © 2019 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft.

In phase-change memory devices, a material is cycled between glassy and crystalline states. The highly temperature-dependent kinetics of its crystallization process enables application in memory technology, but the transition has not been resolved on an atomic scale. Using femtosecond x-ray diffraction and ab initio computer simulations, we determined the time-dependent pair-correlation function of phase-change materials throughout the melt-quenching and crystallization process. We found a liquid–liquid phase transition in the phase-change materials Ag4In3Sb67Te26 and Ge15Sb85 at 660 and 610 kelvin, respectively. The transition is predominantly caused by the onset of Peierls distortions, the amplitude of which correlates with an increase of the apparent activation energy of diffusivity. This reveals a relationship between atomic structure and kinetics, enabling a systematic optimization of the memory-switching kinetics. 2017 © The Authors, some rights reserved

The element specificity of soft X-ray spectroscopy makes it an ideal tool for analyzing the microscopic origin of ultrafast dynamics induced by localized optical excitation in metal-insulator heterostructures. Using [Fe/MgO]n as a model system, we perform ultraviolet pump/soft X-ray probe experiments, which are sensitive to all constituents of these heterostructures, to probe both electronic and lattice excitations. Complementary ultrafast electron diffraction experiments independently analyze the lattice dynamics of the Fe constituent, and together with ab initio calculations yield comprehensive insight into the microscopic processes leading to local relaxation within a single constituent or nonlocal relaxation between two constituents. Besides electronic excitations in Fe, which are monitored at the Fe L3 absorption edge and relax within 1 ps by electron-phonon coupling, soft X-ray analysis identifies a change at the oxygen K absorption edge of the MgO layers which occurs within 0.5 ps. This ultrafast energy transfer across the Fe-MgO interface is mediated by high-frequency, interface vibrational modes, which are excited by hot electrons in Fe and couple to vibrations in MgO in a mode-selective, nonthermal manner. A second, slower timescale is identified at the oxygen K pre-edge and the Fe L3 edge. The slower process represents energy transfer by acoustic phonons and contributes to thermalization of the entire heterostructure. We thus find that the interfacial energy transfer is associated with nonequilibrium behavior in the phonon system. Because our experiments lack signatures of charge transfer across the interface, we conclude that phonon-mediated processes dominate the competition of electronic and lattice excitations in these nonlocal, nonequilibrium dynamics. © 2019 American Physical Society.

Monomers and dimers of spherical gold nanoparticles (NPs) exhibit highly uniform plasmonic properties at the single-particle level due to their high structural homogeneity (precision plasmonics). Recent investigations in precision plasmonics have largely focused on static properties using conventional techniques such as transmission electron microscopy and optical dark-field microscopy. In this Feature Article, we first highlight the application of femtosecond time-resolved electron diffraction for monitoring the nonequilibrium dynamics of spherical gold NPs after ultrafast optical excitation. The analysis of the transient diffraction patterns allows us to directly obtain quantitative information on the incoherent excitation of the lattice, that is, heating upon electron-lattice equilibration, as well as on the development of strain due to lattice expansion on picosecond time scales. The controlled assembly of two spherical gold NPs into a dimer with a few nanometers gap leads to unique optical properties. Specifically, extremely high electric fields (hot spot) in the gap are generated upon resonant optical excitation. Conventional optical microscopy cannot spatially resolve this unique hot spot due to the optical diffraction limit. We therefore employed nonlinear photoemission electron microscopy to visualize hot spots in single dimers of spherical gold NPs. A quantitative comparison of different single dimers confirms the homogeneity of the hot spots on the single-particle level. Overall, these initial results are highly encouraging because they pave the way to investigate nonequilibrium dynamics in highly uniform plasmonic nanostructures at the time and space limits. © 2019 American Chemical Society.

In this work, we monitor the onset of nonthermal melting in single-crystal silicon by implementing an x-ray pump-x-ray probe scheme. Using the ultrashort pulses provided by the Linac Coherent Light Source (SLAC) and a custom-built split-and-delay line for hard x rays, we achieve the temporal resolution needed to detect the onset of the transition. Our data show no loss of long-range order up to 150±40 fs from photoabsorption, which we interpret as the time needed for the electronic system to equilibrate at or above the critical nonthermal melting temperature. Once such equilibration is reached, the loss of long-range atomic order proceeds inertially and is completed within 315±40 fs from photoabsorption. © 2018 American Physical Society.

The nanosize effect on electron-phonon interactions in free-electron noble metals has been a subject of intense discussion because of their important applications in physics, chemistry, and biomedicine. However, the interference from supports of dispersive nanoparticulate metals has led to controversial observations. We utilize freestanding, bicontinuous nanoporous gold (NPG) films to investigate electron-phonon interaction dynamics using ultrafast MeV electron diffraction. Compared to solid gold films, NPG shows faster electron-phonon interaction and thus noticeably higher electron-phonon coupling constant. The results demonstrate that surface states of electrons and phonons play an important role in electron-phonon coupling of nanostructured materials. © 2018 American Chemical Society.

The ultrafast laser excitation of matters leads to nonequilibrium states with complex solid-liquid phase-transition dynamics. We used electron diffraction at mega–electron volt energies to visualize the ultrafast melting of gold on the atomic scale length. For energy densities approaching the irreversible melting regime, we first observed heterogeneous melting on time scales of 100 to 1000 picoseconds, transitioning to homogeneous melting that occurs catastrophically within 10 to 20 picoseconds at higher energy densities. We showed evidence for the heterogeneous coexistence of solid and liquid. We determined the ion and electron temperature evolution and found superheated conditions. Our results constrain the electron-ion coupling rate, determine the Debye temperature, and reveal the melting sensitivity to nucleation seeds. © 2017 The Authors

In this reply to S. Durbin's comment on our original paper "Ultrafast terahertz-field-driven ionic response in ferroelectric BaTiO3," we concur that his final equations 8 and 9 more accurately describe the change in diffracted intensity as a function of Ti displacement. We also provide an alternative derivation based on an ensemble average over unit cells. The conclusions of the paper are unaffected by this correction. © 2018 American Physical Society.

We apply time-resolved MeV electron diffraction to study the electron-lattice energy relaxation in thin film Au-insulator heterostructures. Through precise measurements of the transient Debye-Waller-factor, the mean-square atomic displacement is directly determined, which allows to quantitatively follow the temporal evolution of the lattice temperature after short pulse laser excitation. Data obtained over an extended range of laser fluences reveal an increased relaxation rate when the film thickness is reduced or the Au-film is capped with an additional insulator top-layer. This behavior is attributed to a cross-interfacial coupling of excited electrons in the Au film to phonons in the adjacent insulator layer(s). Analysis of the data using the two-temperature-model taking explicitly into account the additional energy loss at the interface(s) allows to deduce the relative strength of the two relaxation channels. © Author(s) 2017.

We have developed a single-shot mega-electronvolt ultrafast-electron-diffraction system to measure the structural dynamics of warm dense matter. The electron probe in this system is featured by a kinetic energy of 3.2 MeV and a total charge of 20 fC, with the FWHM pulse duration and spot size at sample of 350 fs and 120 μm respectively. We demonstrate its unique capability by visualizing the atomic structural changes of warm dense gold formed from a laser-excited 35-nm freestanding single-crystal gold foil. The temporal evolution of the Bragg peak intensity and of the liquid signal during solid-liquid phase transition are quantitatively determined. This experimental capability opens up an exciting opportunity to unravel the atomic dynamics of structural phase transitions in warm dense matter regime. © 2016 Author(s).

The dynamical processes associated with electric field manipulation of the polarization in a ferroelectric remain largely unknown but fundamentally determine the speed and functionality of ferroelectric materials and devices. Here we apply subpicosecond duration, single-cycle terahertz pulses as an ultrafast electric field bias to prototypical BaTiO3 ferroelectric thin films with the atomic-scale response probed by femtosecond x-ray-scattering techniques. We show that electric fields applied perpendicular to the ferroelectric polarization drive large-amplitude displacements of the titanium atoms along the ferroelectric polarization axis, comparable to that of the built-in displacements associated with the intrinsic polarization and incoherent across unit cells. This effect is associated with a dynamic rotation of the ferroelectric polarization switching on and then off on picosecond time scales. These transient polarization modulations are followed by long-lived vibrational heating effects driven by resonant excitation of the ferroelectric soft mode, as reflected in changes in the c-axis tetragonality. The ultrafast structural characterization described here enables a direct comparison with first-principles-based molecular-dynamics simulations, with good agreement obtained. © 2016 American Physical Society.

Ultrafast electron probes are powerful tools, complementary to x-ray free-electron lasers, used to study structural dynamics in material, chemical, and biological sciences. High brightness, relativistic electron beams with femtosecond pulse duration can resolve details of the dynamic processes on atomic time and length scales. SLAC National Accelerator Laboratory recently launched the Ultrafast Electron Diffraction (UED) and microscopy Initiative aiming at developing the next generation ultrafast electron scattering instruments. As the first stage of the Initiative, a mega-electron-volt (MeV) UED system has been constructed and commissioned to serve ultrafast science experiments and instrumentation development. The system operates at 120-Hz repetition rate with outstanding performance. In this paper, we report on the SLAC MeV UED system and its performance, including the reciprocal space resolution, temporal resolution, and machine stability. © 2015 AIP Publishing LLC.

Electron-phonon coupling processes determine electronic transport properties of materials and are responsible for the transfer of electronic excess energy to the lattice. With decreasing device dimensions an understanding of these processes in nanoscale materials is becoming increasingly important. Here we use time-resolved electron diffraction to directly study energy relaxation in thin bismuth films after optical excitation. Precise measurements of the transient Debye-Waller-effect for various film thicknesses and over an extended range of excitation fluences allow to separate different contributions to the incoherent lattice response. While phonon softening in the electronically excited state is responsible for an immediate increase of the r.m.s. atomic displacement within a few hundred fs, 'ordinary' electron-phonon coupling leads to subsequent heating of the material on a few ps time-scale. The data reveal distinct changes in the energy transfer dynamics which becomes faster for stronger excitation and smaller film thickness, respectively. The latter effect is attributed to a cross-interfacial coupling of excited electrons to phonons in the substrate. © 2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Nanoscale dimensions in materials lead to unique electronic and structural properties with applications ranging from site-specific drug delivery to anodes for lithium-ion batteries. These functional properties often involve large-amplitude strains and structural modifications, and thus require an understanding of the dynamics of these processes. Here we use femtosecond X-ray scattering techniques to visualize, in real time and with atomic-scale resolution, light-induced anisotropic strains in nanocrystal spheres and rods. Strains at the percent level are observed in CdS and CdSe samples, associated with a rapid expansion followed by contraction along the nanosphere or nanorod radial direction driven by a transient carrier-induced stress. These morphological changes occur simultaneously with the first steps in the melting transition on hundreds of femtosecond timescales. This work represents the first direct real-time probe of the dynamics of these large-amplitude strains and shape changes in few-nanometre-scale particles. © 2015 Macmillan Publishers Limited. All rights reserved.

Measurement and understanding of the microscopic pathways materials follow as they transform is crucial for the design and synthesis of new metastable phases of matter. Here we employ femtosecond single-shot X-ray diffraction techniques to measure the pathways underlying solid-solid phase transitions in cadmium sulfide nanorods, a model system for a general class of martensitic transformations. Using picosecond rise-time laser-generated shocks to trigger the transformation, we directly observe the transition state dynamics associated with the wurtzite-to-rocksalt structural phase transformation in cadmium sulfide with atomic-scale resolution. A stress-dependent transition path is observed. At high peak stresses, the majority of the sample is converted directly into the rocksalt phase with no evidence of an intermediate prior to rocksalt formation. At lower peak stresses, a transient five-coordinated intermediate structure is observed consistent with previous first principles modeling. © 2014 American Chemical Society.

An all-x-ray pump and probe capability is highly desired for the free-electron laser community. A possible implementation involves the use of an x-ray mirror downstream of the sample to backreflect the pump beam onto itself. We expose silicon single crystals, a candidate for this hard-x-ray mirror, to the hard-x-ray beam of the Linac Coherent Light Source (SLAC National Acceleration Laboratory) to assess its suitability. We find that silicon is an appropriate mirror material, but its reflectivity at high x-ray fluences is somewhat unpredictable. We attribute this behavior to x-ray-induced local damage in the mirror, which we have characterized post mortem via microdiffraction, scanning electron microscopy, and Raman spectroscopy. We demonstrate a strategy to reduce local damage by using a structured silicon-based mirror. Preliminary results suggest that the latter yields reproducible Bragg reflectivity at high x-ray fluences, promising a path forward for silicon single crystals as x-ray backreflectors. © 2014 American Physical Society.

In this article, we describe the experimental station and procedures for investigating the interaction of short-wavelength free-electron lasers (FELs) pulses with solids. With the advent of these sources, a unique combination of radiation properties (including wavelength range from tens of nanometers down to sub-Angstroms, femtosecond pulse duration, and high pulse energy reaching milli-Joules level) creates new research possibilities for the systematic studies of radiation-induced structural changes in solids. However, the properties of the intense FEL radiation generate, apart from the new experimental opportunities, extreme demands on the experimental set-up (mostly in terms of radiation hardness of detectors and their saturation levels). Thus, radiation-induced phase transitions in solids, beyond the fundamental scientific interest, are of importance for the design of FEL beamlines and instruments which interact with the direct beam. In this report, we focus on the instrumentation and experimental techniques used in the recent studies performed at the FLASH facility in Hamburg. © 2013 IOP Publishing Ltd and Sissa Medialab srl.

The macroscopic characteristics of a material are determined by its elementary excitations, which dictate the response of the system to external stimuli. The spectrum of excitations is related to fluctuations in the density-density correlations and is typically measured through frequency-domain neutron or X-ray scattering. Time-domain measurements of these correlations could yield a more direct way to investigate the excitations of solids and their couplings both near to and far from equilibrium. Here we show that we can access large portions of the phonon dispersion of germanium by measuring the diffuse scattering from femtosecond X-ray free-electron laser pulses. A femtosecond optical laser pulse slightly quenches the vibrational frequencies, producing pairs of high-wavevector phonons with opposite momenta. These phonons manifest themselves as time-dependent coherences in the displacement correlations probed by the X-ray scattering. As the coherences are preferentially created in regions of strong electron-phonon coupling, the time-resolved approach is a natural spectroscopic tool for probing low-energy collective excitations in solids, and their microscopic interactions. © 2013 Macmillan Publishers Limited.

The resolution of ultrafast studies performed at extreme ultraviolet and X-ray free-electron lasers is still limited by shot-to-shot variations of the temporal pulse characteristics. Here we show a versatile single-shot temporal diagnostic tool that allows the determination of the extreme ultraviolet pulse duration and the relative arrival time with respect to an external pump-probe laser pulse. This method is based on time-resolved optical probing of the transient reflectivity change due to linear absorption of the extreme ultraviolet pulse within a solid material. In this work, we present measurements performed at the FLASH free-electron laser. We determine the pulse duration at two distinct wavelengths, yielding (184±14) fs at 41.5 nm and (21±19) fs at 5.5 nm. Furthermore, we demonstrate the feasibility to operate the tool as an online diagnostic by using a 20-nm-thin Si 3N4 membrane as target. Our results are supported by detailed numerical and analytical investigations. © 2013 Macmillan Publishers Limited. All rights reserved.

Time-resolved diffuse X-ray scattering with 50 fs, 9.5 keV X-ray pulses from the Linear Coherent Light Source was used to study the structural dynamics in materials undergoing rapid melting and ablation after fs laser excitation. © Owned by the authors, published by EDP Sciences, 2013.

Time-resolved x-ray diffraction with ultrashort x-ray pulses from a laser-produced plasma is used to study the lattice response of FeRh during a femtosecond laser-induced antiferromagnetic (AFM) to ferromagnetic (FM) phase transition. Pump-probe measurements at initial sample temperatures below as well as above the AFM-to-FM transition temperature and for different laser pump fluences allowed to disentangle the various contributions driving lattice expansion. In particular, the data reveal that the structural changes associated with the magnetic phase transition occur on a time scale of a hundred picoseconds. © 2012 American Physical Society.

We show that light drives large-amplitude structural changes in thin films of the prototypical ferroelectric PbTiO 3 via direct coupling to its intrinsic photovoltaic response. Using time-resolved x-ray scattering to visualize atomic displacements on femtosecond time scales, photoinduced changes in the unit-cell tetragonality are observed. These are driven by the motion of photogenerated free charges within the ferroelectric and can be simply explained by a model including both shift and screening currents, associated with the displacement of electrons first antiparallel to and then parallel to the ferroelectric polarization direction. © 2012 American Physical Society.

We used photon pulses from an x-ray free-electron laser to study ultrafast x-ray-induced transitions of graphite from solid to liquid and plasma states. This was accomplished by isochoric heating of graphite samples and simultaneous probing via Bragg and diffuse scattering at high time resolution. We observe that disintegration of the crystal lattice and ion heating of up to 5 eV occur within tens of femtoseconds. The threshold fluence for Bragg-peak degradation is smaller and the ion-heating rate is faster than current x-ray-matter interaction models predict. © 2012 American Physical Society.

We apply time-resolved x-ray diffraction using ultrashort x-ray pulses from a laser-produced plasma to probe the picosecond acoustic response of a thin laser-heated gold film. Measurements of the temporal changes in the angular distribution of diffracted x-rays provide direct quantitative information on the transient evolution of lattice strain. This allows to disentangle electronic and thermal pressure contributions driving lattice expansion after impulsive laser excitation. The electron-lattice energy equilibration time τE = (5±0.3) ps as well as the electronic Grüneisen parameter γe = (1.48±0.3) have been determined. © 2011 American Institute of Physics.

We apply ultrafast time-resolved X-ray diffraction to directly study coherent acoustic and optical phonons in laser-excited materials. In Au the ps acoustic response has been investigated with the particular goal to clarify the interplay of electronic and thermal pressure contributions. In Bi the extreme softening of the coherently excited A1g optical phonon presents strong indication that upon intense laser-excitation the Peierls-transition which determines the equilibrium structure of Bi can be reversed. In FeRh we studied the lattice response after a fast laser-induced anti-ferromagnetic to ferromagnetic phase transition. © 2010 American Institute of Physics.

The structural dynamics of short-pulse laser irradiated surfaces and nano-structures has been studied with nm spatial and ultrafast temporal resolution by means of single-shot coherent XUV-scattering techniques. The experiments allowed us to time-resolve the formation of laser-induced periodic surface structures, and to follow the expansion and disintegration of nano-objects during laser ablation. © 2010 American Institute of Physics.

We investigated single shot damage of Mo/Si multilayer coatings exposed to the intense fs XUV radiation at the Free-electron LASer facility in Hamburg - FLASH. The interaction process was studied in situ by XUV reflectometry, time resolved optical microscopy, and "post-mortem" by interference- polarizing optical microscopy (with Nomarski contrast), atomic force microscopy, and scanning transmission electron microcopy. An ultrafast molybdenum silicide formation due to enhanced atomic diffusion in melted silicon has been determined to be the key process in the damage mechanism. The influence of the energy diffusion on the damage process was estimated. The results are of significance for the design of multilayer optics for a new generation of pulsed (from atto- to nanosecond) XUV sources. © 2010 Optical Society of America.