Spatially patterned extreme ultraviolet light pulses can be used for probing multiple dynamical processes at the nanoscale.

Significance: The European XFEL is a hard X-ray Free-Electron Laser (FEL) with pulse repetition rates in the megahertz regime. Thus, sample dynamics in the microsecond and submicrosecond regime can be accessed by means of X-ray photon correlation spectroscopy (XPCS). Application of XPCS at FEL sources has been challenged because of the intrinsic fluctuations of FELs and the radiation-induced sample heating and damage. In this work we demonstrate the unprecedented stability of the European XFEL and show the feasibility of microsecond XPCS on a model system. Nonlinear heating on microsecond timescales is observed reaching superheated water states that persist up to 100 μs. Our data indicate a violation of the Stokes–Einstein relation for nanoparticle diffusion at short times.

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.

How residual stresses in colloids generate directional and heterogeneous motions down to fundamental length scales.

We report on new opportunities for ultrafast science thanks to the use of two-colour extreme ultraviolet (XUV) pulses at the FERMI free electron laser (FEL) facility. The two pulses have been employed to carry out a pioneering FEL-pump/FEL-probe diffraction experiment using a Ti target and tuning the FEL pulses to the M_2/3-edge in order to explore the dependence of the dielectric constant on the excitation fluence. The future impact that the use of such a two-colour FEL emission will have on the development of ultrafast wave-mixing methods in the XUV/soft X-ray range is addressed and discussed.

The liquid-to-solid phase transition is a complex process that is difficult to investigate experimentally with sufficient spatial and temporal resolution. A key aspect of the transition is the formation of a critical seed of the crystalline phase in a supercooled liquid, that is, a liquid in a metastable state below the melting temperature. This stochastic process is commonly described within the framework of classical nucleation theory, but accurate tests of the theory in atomic and molecular liquids are challenging. Here, we employ femtosecond x-ray diffraction from microscopic liquid jets to study crystal nucleation in supercooled liquids of the rare gases argon and krypton. Our results provide stringent limits to the validity of classical nucleation theory in atomic liquids, and offer the long-sought possibility of testing nonclassical extensions of the theory.