X-ray spectroscopy station for sample characterization at ELI Beamlines.

X-ray spectroscopy is a demanded tool across multiple user communities. Here we report on a new station for X-ray emission spectroscopy at the Extreme Light Infrastructure Beamlines Facility. The instrument utilizes the von Hamos geometry and works with a number of different sample types, notably including liquid systems. We demonstrate a simple and reliable method for source position control using two cameras. This approach addresses energy calibration dependence on sample position, which is a characteristic source of measurement uncertainty for wavelength dispersive spectrometers in XES arrangement. We also present a straightforward procedure for energy calibration of liquid and powder samples to a thin film reference. The developed instrumentation enabled us to perform the first experimental determination of the Kα lines of liquidized K3Fe(CN)6 as well as powdered and liquidized FeNH4(SO4)2. Finally, we report on proof-of-principle use of a colliding jet liquid sample delivery system in an XES experiment.

Time-Resolved XUV Opacity Measurements of Warm Dense Aluminum.

The free-free opacity in plasmas is fundamental to our understanding of energy transport in stellar interiors and for inertial confinement fusion research. However, theoretical predictions in the challenging dense plasma regime are conflicting and there is a dearth of accurate experimental data to allow for direct model validation. Here we present time-resolved transmission measurements in solid-density Al heated by an XUV free-electron laser. We use a novel functional optimization approach to extract the temperature-dependent absorption coefficient directly from an oversampled pool of single-shot measurements, and find a pronounced enhancement of the opacity as the plasma is heated to temperatures of order of the Fermi energy. Plasma heating and opacity enhancement are observed on ultrafast timescales, within the duration of the femtosecond XUV pulse. We attribute further rises in the opacity on ps timescales to melt and the formation of warm dense matter.

High-flux source of coherent XUV pulses for user applications.

We present experimental results obtained at a user-oriented XUV beamline implemented at the ELI Beamlines facility. The coherent XUV radiation is produced via high harmonic generation in gases in a loose focusing geometry. The beamline is designed to be driven by 1 kHz, 100 mJ, 20 fs pulses centered at a wavelength of 830 nm. Results such as XUV spectra, beam wavefront and pulse energy obtained during the beamline commissioning with a commercial 1 kHz, 5 mJ, 40 fs laser system are presented. A unique XUV spectrometer for source characterization designed to reach a very high sensitivity is described in detail, and we demonstrate a novel technique for single-shot and every-shot XUV pulse energy measurement.

Molecules for security measures: from keypad locks to advanced communication protocols.

The idea of using molecules in the context of information security has sparked the interest of researchers from many scientific disciplines. This is clearly manifested in the diversity of the molecular platforms and the analytical techniques used for this purpose, some of which we highlight in this Tutorial Review. Moreover, those molecular systems can be used to emulate a broad spectrum of security measures. For a long time, molecular keypad locks enjoyed a clear preference and the review starts off with a description of how these devices developed. In the last few years, however, the field has evolved into something larger. Examples include more complex authentication protocols (multi-factor authentication and one-time passwords), the recognition of erroneous procedures in data transmission (parity devices), as well as steganographic and cryptographic protection.

Transferring the entatic-state principle to copper photochemistry.

The entatic state denotes a distorted coordination geometry of a complex from its typical arrangement that generates an improvement to its function. The entatic-state principle has been observed to apply to copper electron-transfer proteins and it results in a lowering of the reorganization energy of the electron-transfer process. It is thus crucial for a multitude of biochemical processes, but its importance to photoactive complexes is unexplored. Here we study a copper complex-with a specifically designed constraining ligand geometry-that exhibits metal-to-ligand charge-transfer state lifetimes that are very short. The guanidine-quinoline ligand used here acts on the bis(chelated) copper(I) centre, allowing only small structural changes after photoexcitation that result in very fast structural dynamics. The data were collected using a multimethod approach that featured time-resolved ultraviolet-visible, infrared and X-ray absorption and optical emission spectroscopy. Through supporting density functional calculations, we deliver a detailed picture of the structural dynamics in the picosecond-to-nanosecond time range.

An acido- and photochromic molecular device that mimics triode action.

The photo-controlled shift of pH titration curves, describing the acidochromic behaviour of a spiropyran switch network, was harnessed for the realisation of a molecular triode. The intricate network can be correctly interpreted with respect to the pH dependence of the main involved species.

Explosions of xenon clusters in ultraintense femtosecond x-ray pulses from the LCLS free electron laser.

Explosions of large Xe clusters ( ~ 11,000) irradiated by femtosecond pulses of 850 eV x-ray photons focused to an intensity of up to 10(17) W/cm(2) from the Linac Coherent Light Source were investigated experimentally. Measurements of ion charge-state distributions and energy spectra exhibit strong evidence for the formation of a Xe nanoplasma in the intense x-ray pulse. This x-ray produced Xe nanoplasma is accompanied by a three-body recombination and hydrodynamic expansion. These experimental results appear to be consistent with a model in which a spherically exploding nanoplasma is formed inside the Xe cluster and where the plasma temperature is determined by photoionization heating.

Saturated ablation in metal hydrides and acceleration of protons and deuterons to keV energies with a soft-x-ray laser.

Studies of materials under extreme conditions have relevance to a broad area of research, including planetary physics, fusion research, materials science, and structural biology with x-ray lasers. We study such extreme conditions and experimentally probe the interaction between ultrashort soft x-ray pulses and solid targets (metals and their deuterides) at the FLASH free-electron laser where power densities exceeding 10(17) W/cm(2) were reached. Time-of-flight ion spectrometry and crater analysis were used to characterize the interaction. The results show the onset of saturation in the ablation process at power densities above 10(16) W/cm(2). This effect can be linked to a transiently induced x-ray transparency in the solid by the femtosecond x-ray pulse at high power densities. The measured kinetic energies of protons and deuterons ejected from the surface reach several keV and concur with predictions from plasma-expansion models. Simulations of the interactions were performed with a nonlocal thermodynamic equilibrium code with radiation transfer. These calculations return critical depths similar to the observed crater depths and capture the transient surface transparency at higher power densities.

Electronic structure of an XUV photogenerated solid-density aluminum plasma.

By use of high intensity XUV radiation from the FLASH free-electron laser at DESY, we have created highly excited exotic states of matter in solid-density aluminum samples. The XUV intensity is sufficiently high to excite an inner-shell electron from a large fraction of the atoms in the focal region. We show that soft-x-ray emission spectroscopy measurements reveal the electronic temperature and density of this highly excited system immediately after the excitation pulse, with detailed calculations of the electronic structure, based on finite-temperature density functional theory, in good agreement with the experimental results.

Auger electron angular distribution of double core-hole states in the molecular reference frame.

The Linac Coherent Light Source free electron laser is a source of high brightness x rays, 2×10(11) photons in a ∼5 fs pulse, that can be focused to produce double core vacancies through rapid sequential ionization. This enables double core vacancy Auger electron spectroscopy, an entirely new way to study femtosecond chemical dynamics with Auger electrons that probe the local valence structure of molecules near a specific atomic core. Using 1.1 keV photons for sequential x-ray ionization of impulsively aligned molecular nitrogen, we observed a rich single-site double core vacancy Auger electron spectrum near 413 eV, in good agreement with ab initio calculations, and we measured the corresponding Auger electron angle dependence in the molecular frame.

Time-resolved pump-probe experiments at the LCLS.

The first time-resolved x-ray/optical pump-probe experiments at the SLAC Linac Coherent Light Source (LCLS) used a combination of feedback methods and post-analysis binning techniques to synchronize an ultrafast optical laser to the linac-based x-ray laser. Transient molecular nitrogen alignment revival features were resolved in time-dependent x-ray-induced fragmentation spectra. These alignment features were used to find the temporal overlap of the pump and probe pulses. The strong-field dissociation of x-ray generated quasi-bound molecular dications was used to establish the residual timing jitter. This analysis shows that the relative arrival time of the Ti:Sapphire laser and the x-ray pulses had a distribution with a standard deviation of approximately 120 fs. The largest contribution to the jitter noise spectrum was the locking of the laser oscillator to the reference RF of the accelerator, which suggests that simple technical improvements could reduce the jitter to better than 50 fs.

Soft x-ray free electron laser microfocus for exploring matter under extreme conditions.

We have focused a beam (BL3) of FLASH (Free-electron LASer in Hamburg: lambda = 13.5 nm, pulse length 15 fs, pulse energy 10-40 microJ, 5 Hz) using a fine polished off-axis parabola having a focal length of 270 mm and coated with a Mo/Si multilayer with an initial reflectivity of 67% at 13.5 nm. The OAP was mounted and aligned with a picomotor controlled six-axis gimbal. Beam imprints on poly(methyl methacrylate) - PMMA were used to measure focus and the focused beam was used to create isochoric heating of various slab targets. Results show the focal spot has a diameter of < or =1 microm. Observations were correlated with simulations of best focus to provide further relevant information.

Multimeric alpha-lactalbumin from human milk induces apoptosis through a direct effect on cell nuclei.

A fraction from human milk containing spf-multimer alpha-lactalbumin (MAL) induces apoptosis in tumor cells and immature cells but spares mature cells. The mechanism of apoptosis induction and the molecular basis for the difference in susceptibility between tumor cells and healthy cells have not been defined. In this study we examined the interaction of MAL with different cellular compartments, using confocal microscopy and subcellular fractionation. MAL was shown to accumulate in the nuclei of sensitive cells rather than in the cytosol, the vesicular fraction, or the ER-Golgi complex. Nuclear uptake occurred rapidly in cells that were susceptible to the apoptosis-inducing effect, but not in nuclei of resistant cells. Nuclear uptake was through the nuclear pore complex and was critical for the induction of DNA fragmentation, since inhibition of nuclear uptake with WGA rescued digitonin-permeabilized cells from induction of DNA fragmentation. Ca2+ was required for MAL-induced DNA fragmentation but nuclear uptake of MAL was independent of Ca2+. This way MAL differs from most previously described agents in that it crosses the plasma membrane and cytosol, and enters cell nuclei where it induces DNA fragmentation through a direct effect at the nuclear level.