We report recent results on the performance of FLASH (Free Electron Laser in Hamburg) operating at a wavelength of 13.7 nm where unprecedented peak and average powers for a coherent EUV radiation source have been measured. In the saturation regime the peak energy approached 170 µJ for individual pulses while the average energy per pulse reached 70 µJ. The pulse duration was in the region of 10 femtoseconds and peak

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During ultrafast demagnetization of a magnetically ordered solid, angular momentum has to be transferred between the spins, electrons, and phonons in the system on femto- and picosecond timescales. Although the intrinsic spin-transfer mechanisms are intensely debated, additional extrinsic mechanisms arising due to nanoscale heterogeneity have only recently entered the discussion. Here we use femtosecond X-ray pulses from a free-electron laser to study thin film samples with magnetic domain patterns. We observe an infrared-pump-induced change of the spin structure within the domain walls on the sub-picosecond timescale. This domain-topography-dependent contribution connects the intrinsic demagnetization process in each domain with spin-transport processes across the domain walls, demonstrating the importance of spin-dependent electron transport between differently magnetized regions as an ultrafast demagnetization channel. This pathway exists independent from structural inhomogeneities such as chemical interfaces, and gives rise to an ultrafast spatially varying response to optical pump pulses.

Femtosecond time-resolved core-level photoemission spectroscopy with a free-electron laser is used to measure the atomic-site specific charge-order dynamics in the charge-density-wave/Mott insulator 1T -TaS2. After strong photoexcitation, a prompt loss of charge order and subsequent fast equilibration dynamics of the electron-lattice system are observed. On the time scale of electron-phonon thermalization, about 1 ps, the system is driven across a phase transition from a long-range charge ordered state to a quasi-equilibrium state with domain-like short-range charge and lattice order. The experiment opens the way to study the nonequilibrium dynamics of condensed matter systems with full elemental, chemical, and atomic site selectivity.Femtosecond time-resolved spectroscopy has become a powerful tool in condensed matter research because it delivers direct dynamical information at the fundamental time scale of elementary electronic processes [1,2]. The method is particularly useful for complex materials, in which two or more of the lattice, charge, spin, and orbital degrees of freedom are strongly coupled. It allows to determine the nature and strength of the interactions between the degrees of freedom, to identify the dominant interactions, and thus to gain important insights into ground-state properties, thermally driven phase transitions, and, possibly, novel hidden phases [3][4][5][6].An exceedingly fertile ground for the combination of spectral selectivity and femtosecond time resolution has been found in materials, in which the charge and lattice degrees of freedom interact strongly to form a coupled charge-density-wave (CDW)/periodic-latticedistortion (PLD) ground state. The quasiparticle and collective mode dynamics of the CDW/PLD state, the finite electron-lattice coupling time, and the collapse of the electronic gap under strong excitation are now known [4][5][6][7][8][9]. Yet, direct dynamical information on the CDW itself, i.e., on the local charge order, is missing. Specifically, it is not clear how fast a CDW can melt and recondense after impulsive excitation. The present study provides this fundamental piece of information for the layered ref-Employing time-resolved x-ray photoemission spectroscopy (TR-XPS) with a free-electron laser [12,13], we directly measure the melting of a large-amplitude CDW in 1T -TaS 2 at atomic sites in real time. Our results show that long-range charge order collapses promptly after strong optical excitation and that a domain-like quasi-equilibrium CDW/PLD state is reached with a subpicosecond time constant.The model system 1T -TaS 2 is a complex material with a simple basic structure consisting of S-Ta-S sandwiches in which each Ta atom is octahedrally coordinated by six S atoms. The interesting physics in this compound is restricted to the hexagonal Ta layers and results from simultaneously strong electron-phonon and electron-electron interactions. The phase diagram includes a high-temperature metallic phase, incommensurate CDW and nearly commensurate CDW (NCCDW) phases...

By the use of the time domain reflectometry method dielectric measurements were carried out first on methanol mixtures with ethanol and 1-propanol, and second, water mixtures with methanol, ethanol and 1-propanol in the frequency range 10 MHz–20 GHz. The first mixtures show a Debye relaxation and logarithm of the relaxation time is given by a linear function of the mole fraction of methanol. These mixtures have the same chainlike cluster of pure alcohol. The second mixtures show the same trend of the relaxation time in a region 0≤xw<0.83, where xw is the mole fraction of water. In a region 0.83<xw≤1.0, we observe an entirely different behavior, which indicates that the cluster of pure water appears for xw>0.83 and that the cluster must be cyclic, consisting of six molecules.