XUV double-pulses with femtosecond to 650 ps separation from a multilayer-mirror-based split-and-delay unit at FLASH

Extreme ultraviolet (XUV) and X-ray free-electron lasers enable new scientific opportunities. Their ultra-intense coherent femtosecond pulses give unprecedented access to the structure of undepositable nanoscale objects and to transient states of highly excited matter. In order to probe the ultrafast complex light-induced dynamics on the relevant time scales, the multi-purpose end-station CAMP at the free-electron laser FLASH has been complemented by the novel multilayer-mirror-based split-and-delay unit DESC (DElay Stage for CAMP) for time-resolved experiments. XUV double-pulses with delays adjustable from zero femtoseconds up to 650 picoseconds are generated by reflecting under near-normal incidence, exceeding the time range accessible with existing XUV split-and-delay units. Procedures to establish temporal and spatial overlap of the two pulses in CAMP are presented, with emphasis on the optimization of the spatial overlap at long time-delays via time-dependent features, for example in ion spectra of atomic clusters

Dynamiken einzelner Cluster in intensiven Lichtpulsen untersucht mit Ionenspektroskopie und Lichtstreuung

Die Wechselwirkung von ultrakurzen Laserpulsen mit Nanoteilchen wird gegenwärtig intensiv untersucht. Freie-Elektronen-Laser (FEL) im Röntgenbereich erlauben seit kurzem völlig neuartige Untersuchungen. Durch ihre extrem intensiven Pulse wird es möglich werden nicht-kristalline Partikel mit räumlich und zeitlich atomarer Auflösung abzubilden. Im Rahmen dieser Dissertation wurden Cluster mit extrem-ultravioletter (XUV) Strahlung des FLASH-FEL in Hamburg abgebildet, sowie laserinduzierte Prozesse in der Probe mit infraroten (IR) Pulsen untersucht. Für die Experimente wurden ein Fokussier- und ein motorisiertes, vakuumtaugliches Einkoppelsystem entworfen und aufgebaut. In der Wechselwirkungszone wurden IR und XUV Pulse mit dem Clusterstrahl überlappt. Die Xenoncluster wurden in Überschallexpansion hergestellt und erreichten Gröβen von 105 – 1010 Atomen. Die Methode der Einzelclusterstreuung wurde mit Ionenspektroskopie kombiniert, wodurch eine Mittlung der Messsignale über die Clustergröβenverteilung und das Leistungsdichen-Profils des Lasers umgangen werden konnte. Um die enormen Datenmenge, welche mit dieser Methode einhergeht, zu handhaben, wurden eine Reihe von Filter- und Sortieralgorithmen entwickeln. Im Einzelnen wurden folgende Ergebnisse erzielt: Die laserinduzierte Entwicklung des Clusters ist stark abhängig von der Dichte und Temperatur der quasi-freien Elektronen im Nanoplasma. Die Nanoplasmadynamiken wurden in Abhängigkeit von der Clustergröβe und der Laserintensität, sowie des Clustermaterials und der Laserwellenlänge untersucht. Die detektierten Ionenspektren weisen erstaunliche Ähnlichkeit auf, was darauf hinweist, dass sich für sehr groβe Cluster die Dynamiken universal verhalten. Nur die äuβersten Atomlagen explodieren vom Cluster ab, während im inneren Teil Elektronen und Ionen rekombinieren. Für eine zeitaufgelösten Untersuchung wurde die Zweifarben Pump-Probe Technik angewendet. Der XUV bestrahlte Cluster wurde zu einer Dichte expandiert, bei der die Mie Resonanz auftritt, welche von dem IR Puls abgefragt wurde. In einer Clustergröβen-abhängigen Untersuchung konnte der mittlere Ladungszustand vor der Rekombination bestimmt werden. Durch Umkehr der Pump-Probe Reihenfolge war es möglich die unterschiedliche Zerfallsstadien der IR induzierten Clusterexpansion mittels kohärenter Röntgenbeugung abzubilden. Aus einem Abnehmen der Streusignalintensität bei hohen Winkeln konnte ein Abschmelzen der Cluster-Oberfläche gefolgert werden. Das konnte mittels einfacher, schneller 2D Fouriertransformationen bestätigt werden, welche gleichzeitig zeigen, dass der zentrale Teil des Clusters auf einer Pikosekunden-Zeitskala intakt bleibt. Diese langsame Entwicklung des Clusterkerns wurde durch Ionensignal mit hohen kinetischen Energien bestätigt – selbst eine Nanosekunde nach Initialisierung der Expansion. Speckle-Muster in den Streubildern zeigen den langsam expandierenden neutralen Zentralpart, der in erster Linie durch einen Anstieg der Temperatur und nur zum geringen Teil durch Coulombkräfte auseinander driftet. Aus der mittleren Speckle-Gröβe lässt sich der mittlere Radius des Clusters zur Zeit seiner Abbildung bestimmen. Eine Modulation der Einhüllenden der Speckle-Intensität resultiert aus Dichte-Fluktuationen innerhalb des zerfallenden Clusters. Durch numerische Streusimulationen konnten die Hauptcharakteristika des gemessenen Speckle-Bildes reproduziert werden.The advent of x-ray free-electron lasers (FELs) has added a new twist to the field of interaction between ultrafast laser pulses and nanoscale matter. The vision to image non-crystalline targets in flight with atomic resolution in space and time is now within reach. This thesis explores the laser induced dynamics of clusters with extreme ultraviolet (XUV) radiation from the FLASH FEL in Hamburg as well as with infrared (IR) laser pulses from a Ti:Sapphire system. An infrared laser focusing unit and a motorized in-vacuum incoupling system were designed for the experiments in this thesis. IR and XUV pulses were guided into the interaction region where they intersect the cluster beam. Large single xenon clusters were produced in supersonic expansion under extreme conditions reaching a size range between 10 and 1000 nanometer in radius. A method of coincident single-shot single-particle imaging and ion spectroscopy was applied, which allows circumventing constrains of signal averaging due to cluster size distributions and FEL power density profiles. A set of filtering and sorting algorithms was developed to handle the large amount of collected data demanded by this method. The laser-induced cluster evolution is highly dependent on quasi-free electron density and temperature. Nanoplasma dynamics were investigated dependent on cluster size and material composition as well as laser intensity and wavelength to gain insight into their correlation with experimental parameters. Astonishingly similar ion time-of-flight spectra were found for very different conditions, i.e. metal and rare-gas clusters as well as IR and XUV radiation. This reveals that very large clusters have universal dynamics in common: only the outermost atomic layers explode and strong recombination takes place in the inner core. For time resolved investigation, a two colour pump-probe technique was employed. The XUV irradiated cluster expanded to a density where the Mie resonance condition was matched and probed by the IR pulse. The average charge state created in clusters of well-defined size did not change with FEL intensity. Furthermore, the average charge state before recombination is derived from analytical calculations using the nanoplasma model. In a reversed pump-probe scheme the IR-induced expansion was imaged. A plasma-driven surface melting could be traced in a decreasing scattering signal at large angle. The verification with basic 2D fast Fourier transforms revealed that the central part of the cluster stays intact on a picosecond timescale. A slow evolution of the cluster is also witnessed from ion signal with high kinetic energies, even a nanosecond after IR irradiation. A novel type of scattering patterns - speckles - traces a slowly expanding neutral core, driven by the hot electron gas in the nanoplasma. From the average speckle size the average cluster radius at the time of detection can be gained. A modulation of the speckle intensity envelope results from a density fluctuation inside the disintegrating cluster. The key features of the measured speckle pattern could be reproduced in scattering simulations using a numerical scalar approach

Exploring the physical–digital interface in blockchain applications: Insights from the luxury watch industry

Counterfeit products are an increasing issue across the luxury sector. Blockchain applications exhibit the potential to mitigate counterfeit risks and facilitate the growing secondary markets by enabling product authentication and digital proof of ownership. In this study, we adopt a qualitative multiple-case study design and conduct interviews with informants from four blockchain projects in the Swiss luxury watch industry. We identify the industry-specific drivers and barriers to blockchain adoption and specifically explore the challenges at the physical–digital interface. Beyond an in-depth description of the problems, our findings suggest two main data management hurdles related to the validity of input data and data synchronicity. The main challenge, however, is to establish an unequivocal link between the physical watch to its digital record on the blockchain. We present several invasive and non-invasive linking approaches and discuss their potential advantages and disadvantages. Further, we outline different areas for future research. Overall, our study addresses a timely issue of blockchain applications, contributing to the operations and supply chain management literature and supporting blockchain use case design in practice.ISSN:1366-554

Generation and structure of extremely large clusters in pulsed jets

Extremely large xenon clusters with sizes exceeding the predictions of the Hagena scaling law by several orders of magnitude are shown to be produced in pulsed gas jets. The cluster sizes are determined using single-shot single-particle imaging experiments with short-wavelength light pulses from the free-electron laser in Hamburg (FLASH). Scanning the time delay between the pulsed cluster source and the intense femtosecond x-ray pulses first shows a main plateau with size distributions in line with the scaling laws, which is followed by an after-pulse of giant clusters. For the extremely large clusters with radii of several hundred nanometers the x-ray scattering patterns indicate a grainy substructure of the particles, suggesting that they grow by cluster coagulation

The 3D-Architecture of Individual Free Silver Nanoparticles Captured by X-Ray Scattering

The diversity of nanoparticle shapes generated by condensation from gaseous matter reflects the fundamental competition between thermodynamic equilibration and the persistence of metastable configurations during growth. In the kinetically limited regime, intermediate geometries that are favoured only in early formation stages can be imprinted in the finally observed ensemble of differently structured specimens. Here we demonstrate that single-shot wide-angle scattering of femtosecond soft X-ray free-electron laser pulses allows three-dimensional characterization of the resulting metastable nanoparticle structures. For individual free silver particles, which can be considered frozen in space for the duration of photon exposure, both shape and orientation are uncovered from measured scattering images. We identify regular shapes, including species with fivefold symmetry and surprisingly large aspect ratio up to particle radii of the order of 100 nm. Our approach includes scattering effects beyond Born’s approximation and is remarkably efficient—opening up new routes in ultrafast nanophysics and free-electron laser science.ISSN:2041-172

Time-resolved x-ray imaging of a laser-induced nanoplasma and its neutral residuals

The evolution of individual, large gas-phase xenon clusters, turned into a nanoplasma by a high power infrared laser pulse, is tracked from femtoseconds up to nanoseconds after laser excitation via coherent diffractive imaging, using ultra-short soft x-ray free electron laser pulses. A decline of scattering signal at high detection angles with increasing time delay indicates a softening of the cluster surface. Here we demonstrate, for the first time a representative speckle pattern of a new stage of cluster expansion for xenon clusters after a nanosecond irradiation. The analysis of the measured average speckle size and the envelope of the intensity distribution reveals a mean cluster size and length scale of internal density fluctuations. The measured diffraction patterns were reproduced by scattering simulations which assumed that the cluster expands with pronounced internal density fluctuations hundreds of picoseconds after excitation.ISSN:1367-263

Imaging plasma formation in isolated nanoparticles with ultrafast resonant scattering ARTICLES YOU MAY BE INTERESTED IN

We have recorded the diffraction patterns from individual xenon clusters irradiated with intense extreme ultraviolet pulses to investigate the influence of light-induced electronic changes on the scattering response. The clusters were irradiated with short wavelength pulses in the wavelength regime of different 4d inner-shell resonances of neutral and ionic xenon, resulting in distinctly different optical properties from areas in the clusters with lower or higher charge states. The data show the emergence of a transient structure with a spatial extension of tens of nanometers within the otherwise homogeneous sample. Simulations indicate that ionization and nanoplasma formation result in a light-induced outer shell in the cluster with a strongly altered refractive index. The presented resonant scattering approach enables imaging of ultrafast electron dynamics on their natural timescale

The role of transient resonances for ultra-fast imaging of single sucrose nanoclusters

Intense x-ray free-electron laser (XFEL) pulses hold great promise for imaging function in nanoscale and biological systems with atomic resolution. So far, however, the spatial resolution obtained from single shot experiments lags averaging static experiments. Here we report on a combined computational and experimental study about ultrafast diffractive imaging of sucrose clusters which are benchmark organic samples. Our theoretical model matches the experimental data from the water window to the keV x-ray regime. The large-scale dynamic scattering calculations reveal that transient phenomena driven by non-linear x-ray interaction are decisive for ultrafast imaging applications. Our study illuminates the complex interplay of the imaging process with the rapidly changing transient electronic structures in XFEL experiments and shows how computational models allow optimization of the parameters for ultrafast imaging experiments. X-ray free electron lasers provide high photon flux to explore single particle diffraction imaging of biological samples. Here the authors present dynamic electronic structure calculations and benchmark them to single-particle XFEL diffraction data of sucrose clusters to predict optimal single-shot imaging conditions