Publisher Correction: Coherent diffractive imaging of single helium nanodroplets with a high harmonic generation source

In the original version of this Article, the affiliation for Luca Poletto was incorrectly given as ‘European XFEL GmbH, Holzkoppel 4, 22869 Schenefeld, Hamburg, Germany’, instead of the correct ‘CNR, Istituto di Fotonica e Nanotecnologie Padova, Via Trasea 7, 35131 Padova, Italy’. This has now been corrected in both the PDF and HTML versions of the Article

Thin-disk laser-pumped OPCPA system delivering 4.4 TW few-cycle pulses

We present an optical parametric chirped pulse amplification (OPCPA) system delivering 4.4 TW pulses centered at 810 nm with a sub-9 fs duration and a carrier-envelope phase stability of 350 mrad. The OPCPA setup pumped by sub-10 ps pulses from two Yb:YAG thin-disk lasers at 100 Hz repetition rate is optimized for a high conversion-efficiency. The terawatt pulses of the OPCPA are utilized for generating intense extreme ultraviolet (XUV) pulses by high-order harmonic generation, achieving XUV pulse energies approaching the microjoule level. © 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen

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

Melting, bubble-like expansion and explosion of superheated plasmonic nanoparticles

We report on time-resolved coherent diffraction imaging of gas-phase silver nanoparticles, strongly heated via their plasmon resonance. The x-ray diffraction images reveal a broad range of phenomena for different excitation strengths, from simple melting over strong cavitation to explosive disintegration. Molecular dynamics simulations fully reproduce this behavior and show that the heating induces rather similar trajectories through the phase diagram in all cases, with the very different outcomes being due only to whether and where the stability limit of the metastable superheated liquid is crossed.Comment: 17 pages, 8 figures (including supplemental material

CAMP@FLASH: an end-station for imaging, electron- and ion-spectroscopy, and pump–probe experiments at the FLASH free-electron laser

The non-monochromatic beamline BL1 at the FLASH free-electron laser facility at DESY was upgraded with new transport and focusing optics, and a new permanent end-station, CAMP, was installed. This multi-purpose instrument is optimized for electron- and ion-spectroscopy, imaging and pump–probe experiments at free-electron lasers. It can be equipped with various electron- and ion-spectrometers, along with large-area single-photon-counting pnCCD X-ray detectors, thus enabling a wide range of experiments from atomic, molecular, and cluster physics to material and energy science, chemistry and biology. Here, an overview of the layout, the beam transport and focusing capabilities, and the experimental possibilities of this new end-station are presented, as well as results from its commissioning

Intergenerational impacts of maternal mortality: Qualitative findings from rural Malawi

Background: Maternal mortality, although largely preventable, remains unacceptably high in developing countries such as Malawi and creates a number of intergenerational impacts. Few studies have investigated the far-reaching impacts of maternal death beyond infant survival. This study demonstrates the short- and long-term impacts of maternal death on children, families, and the community in order to raise awareness of the true costs of maternal mortality and poor maternal health care in Neno, a rural and remote district in Malawi. Methods: Qualitative in-depth interviews were conducted to assess the impact of maternal mortality on child, family, and community well-being. We conducted 20 key informant interviews, 20 stakeholder interviews, and six sex-stratified focus group discussions in the seven health centers that cover the district. Transcripts were translated, coded, and analyzed in NVivo 10. Results: Participants noted a number of far-reaching impacts on orphaned children, their new caretakers, and extended families following a maternal death. Female relatives typically took on caregiving responsibilities for orphaned children, regardless of the accompanying financial hardship and frequent lack of familial or governmental support. Maternal death exacerbated children’s vulnerabilities to long-term health and social impacts related to nutrition, education, employment, early partnership, pregnancy, and caretaking. Impacts were particularly salient for female children who were often forced to take on the majority of the household responsibilities. Participants cited a number of barriers to accessing quality child health care or support services, and many were unaware of programming available to assist them in raising orphaned children or how to access these services. Conclusions: In order to both reduce preventable maternal mortality and diminish the impacts on children, extended families, and communities, our findings highlight the importance of financing and implementing universal access to emergency obstetric and neonatal care, and contraception, as well as social protection programs, including among remote populations

Time-resolved dynamics of clusters in intense extreme ultraviolet double-pulses

With their brilliant short-wavelength light pulses, free-electron lasers (FEL) enable an unique insight into the interaction of light and matter. By recording scattering patterns, coherent diffractive imaging allows to image and investigate single nanometer-sized particles. If such an intense light pulse intersects with a nanoparticle, it will be ionized multiple times and a sequence of mainly non-linear processes is initiated. In particular, the particle will expand, which may extend over several time scales and finally leads to complete fragmentation, accompanied by relaxation processes like electron-ion recombination. A time-resolved investigation can be achieved with two light pulses, whereby the pump pulse starts the dynamics and the probe pulse samples it. To generate two light pulses with an adjustable time delay of up to half a nanosecond, in this thesis, the split-and-delay unit „Delay Stage for CAMP“ (DESC) was set up at the „Free-Electron Laser in Hamburg“ (FLASH) of the „Deutsches Elektronen-Synchrotron“ (DESY). With this it was possible to investigate the non-linear interaction in xenon clusters in a time-resolved manner. For this purpose, at a wavelength of 13.5nm ( ≙ 91.8eV) scattering patterns of xenon cluster were recorded with the novel experimental concept „X-Ray-Movie-Camera“. Here a scattering pattern of an original xenon cluster with the pump pulse and a scattering pattern of the light induced dynamics in the same cluster was imaged with the probe pulse. The measurement of pairs of scattering patterns demonstrates the success of this new experimental approach. Further, at lower power densities, where a scattering pattern can just be detected, even 650ps after the pump pulse intact xenon clusters without any sign of expansion were abserved. At higher power densities, also fragmenting clusters could be imaged. Also it was possible to record time-resolved averaged ion spectra for several smaller cluster sizes and to follow the recombination and expansion behaviour on a currently unexplored time scale. A with the time delay increasing mean charge state was observed, which suggest a reduced recombination due to the expansion initiated by the pump pulse. Signs of recombination were still found at maximum time delay and allow to conclude the incomplete fragmentation of the cluster. This further enables the detection of higher charge states, which apparently preferentially recombine and otherwise remain hidden when excited with a single light pulse. The investigation of the kinetic energies of the ions in particular permits an insight into the interplay of expansion and recombination. With the X-Ray-Movie-Camera a novel method for the investigation of light-matter interaction in single nanoparticles has been developed. In combination with the double pulses from DESC, it can be traced over many time scales.Mit ihren brillanten kurzwelligen Lichtpulsen ermöglichen Freie-Elektronen-Laser (FEL) einen einzigartigen Einblick in die Wechselwirkung von Licht und Materie. Mittels kohärenter Lichtstreuung gelingt es durch die Aufnahme von Streubildern einzelne Nanometer große Partikel abzubilden und zu untersuchen. Trifft solch ein intensiver Lichtpuls auf einen Nanopartikel, wird dieser vielfach ionisiert und eine Folge großteils nichtlinearer Prozesse initiiert. Insbesondere kommt es zur Expansion, die mehrere Zeitskalen überdauern kann und letztlich zur vollständigen Fragmentation führt, begleitet von Relaxationsprozessen wie Elektron-Ion-Rekombination. Eine zeitaufgelöste Untersuchung ist mit zwei Lichtpulsen möglich, wobei der Pumppuls die Dynamik startet und der Probepuls diese abfragt. Zur Erzeugung zweier Lichtpulse mit einer einstellbaren Zeitverzögerung von bis zu einer halben Nanosekunde wurde in dieser Arbeit die Strahlteiler- und Verzögerungseinheit „Delay Stage for CAMP“ (DESC) am „Free-Electron Laser in Hamburg“ (FLASH) beim „Deutschen Elektronen-Synchrotron“ (DESY) aufgebaut. Mit dieser ist es gelungen, die nichtlineare Wechselwirkung in Xenonclustern zeitaufgelöst zu untersuchen. Dazu wurde bei 13,5nm Wellenlänge ( ≙ 91,8eV) mit dem neuartigen experimentellen Konzept „X-Ray-Movie-Camera“ mit dem Pumppuls ein Streubild eines ursprünglichen Xenonclusters und mit dem Probepuls ein Streubild von der lichtinduzierten Dynamik in demselben Cluster aufgezeichnet. Anhand der Streubildpaare der Xenoncluster kann zum einen der Erfolg dieses neuen experimentellen Ansatzes belegt werden. Zum anderen wird beobachtet, dass bei niedrigen Leistungsdichten, mit denen gerade noch ein Streubild detektiert werden kann, einige Xenoncluster auch 650ps nach dem Pumppuls noch weitgehend intakt sind und dass es bei diesen keine Anzeichen einer Expansion gibt. Bei höheren Leistungsdichten konnten auch fragmentierende Cluster abgebildet werden. Weiterhin ist es gelungen, für mehrere kleinere Clustergrößen zeitaufgelöste gemittelte Ionenspektren aufzuzeichnen und das Rekombinations- und Expansionsverhalten auf einer bisher unerforschten Zeitskala zu verfolgen. Es lässt sich mit der Zeitverzögerung ein zunehmender mittlerer Ladungszustand beobachten, der auf eine verminderte Rekombination infolge der durch den Pumppuls initiierten Expansion schließen lässt. Rekombination wird aber auch noch bei maximaler Zeitverzögerung beobachtet, was eine unvollständige Fragmentation der Cluster folgern lässt. Hiermit gelingt auch der Nachweis höherer Ladungszustände, die offenbar bevorzugt rekombinieren und bei Anregung mit nur einem Lichtpuls verborgen bleiben. Die Untersuchung der kinetischen Energien der Ionen erlaubt insbesondere einen Einblick in das Wechselspiel von Expansion und Rekombination. Mit der X-Ray-Movie-Camera ist eine neuartige Methode zur Untersuchung der Licht-Materie-Wechselwirkung in einzelnen Nanopartikeln entwickelt worden. Zusammen mit den Doppelpulsen von DESC kann diese über viele Zeitskalen verfolgt werden

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

Thin-disk laser-pumped OPCPA system delivering 44 TW few-cycle pulses

ISSN:1094-408

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