Recombination dynamics of clusters in intense extreme-ultraviolet and near- infrared fields

We investigate electron-ion recombination processes in clusters exposed to intense extreme-ultraviolet (XUV) or near-infrared (NIR) pulses. Using the technique of reionization of excited atoms from recombination (REAR), recently introduced in Schütte et al (2014 Phys. Rev. Lett. 112 253401), a large population of excited atoms, which are formed in the nanoplasma during cluster expansion, is identified under both ionization conditions. For intense XUV ionization of clusters, we find that the significance of recombination increases for increasing cluster sizes. In addition, larger fragments are strongly affected by recombination as well, as shown for the case of dimers. We demonstrate that for mixed Ar–Xe clusters exposed to intense NIR pulses, excited atoms and ions are preferentially formed in the Xe core. As a result of electron-ion recombination, higher charge states of Xe are efficiently suppressed, leading to an overall reduced expansion speed of the cluster core in comparison to the shell

Recombination dynamics of clusters in intense extreme-ultraviolet and near-infrared fields

We investigate electron-ion recombination processes in clusters exposed to intense extreme-ultraviolet (XUV) or near-infrared (NIR) pulses. Using the technique of reionization of excited atoms from recombination (REAR), recently introduced in Schütte et al (2014 Phys. Rev. Lett. 112 253401), a large population of excited atoms, which are formed in the nanoplasma during cluster expansion, is identified under both ionization conditions. For intense XUV ionization of clusters, we find that the significance of recombination increases for increasing cluster sizes. In addition, larger fragments are strongly affected by recombination as well, as shown for the case of dimers. We demonstrate that for mixed Ar–Xe clusters exposed to intense NIR pulses, excited atoms and ions are preferentially formed in the Xe core. As a result of electron-ion recombination, higher charge states of Xe are efficiently suppressed, leading to an overall reduced expansion speed of the cluster core in comparison to the shell

Ecological Drivers of Habitat Use by Meso Mammals in a Miombo Ecosystem in the Issa Valley, Tanzania

Vast stretches of East and Southern Africa are characterized by a mosaic of deciduous woodlands and evergreen riparian forests, commonly referred to as “miombo,” hosting a high diversity of plant and animal life. However, very little is known about the communities of small-sized mammals inhabiting this heterogeneous biome. We here document the diversity and abundance of 0.5–15 kg sized mammals (“meso-mammals”) in a relatively undisturbed miombo mosaic in western Tanzania, using 42 camera traps deployed over a 3 year-period. Despite a relatively low diversity of meso-mammal species (n = 19), these comprised a mixture of savanna and forest species, with the latter by far the most abundant. Our results show that densely forested sites are more intensely utilized than deciduous woodlands, suggesting riparian forest within the miombo matrix might be of key importance to meso-mammal populations. Some species were captured significantly more often in proximity to (and sometimes feeding on) termite mounds (genus Macrotermes), as they are a crucial food resource. There was some evidence of temporal partitioning in activity patterns, suggesting hetero-specific avoidance to reduce foraging competition. We compare our findings to those of other miombo sites in south-central Africa

Recombination dynamics of clusters in intense extreme-ultraviolet and near-infrared fields

We investigate electron-ion recombination processes in clusters exposed to intense extreme-ultraviolet (XUV) or near-infrared (NIR) pulses. Using the technique of reionization of excited atoms from recombination (REAR), recently introduced in Schütte et al (2014 Phys. Rev. Lett. 112 253401), a large population of excited atoms, which are formed in the nanoplasma during cluster expansion, is identified under both ionization conditions. For intense XUV ionization of clusters, we find that the significance of recombination increases for increasing cluster sizes. In addition, larger fragments are strongly affected by recombination as well, as shown for the case of dimers. We demonstrate that for mixed Ar–Xe clusters exposed to intense NIR pulses, excited atoms and ions are preferentially formed in the Xe core. As a result of electron-ion recombination, higher charge states of Xe are efficiently suppressed, leading to an overall reduced expansion speed of the cluster core in comparison to the shell

THz streak camera performance for single-shot characterization of XUV pulses with complex temporal structures

The THz-field-driven streak camera has proven to be a powerful diagnostic-technique that enables the shot-to-shot characterization of the duration and the arrival time jitter of free electron laser (FEL) pulses. Here we investigate the performance of three computational approaches capable to determine the duration of FEL pulses with complex temporal structures from single-shot measurements of up to three simultaneously recorded spectra. We use numerically simulated FEL pulses in order to validate the accuracy of the pulse length retrieval in average as well as in a single-shot mode. We discuss requirements for the THz field strength in order to achieve reliable results and compare our numerical study with the analysis of experimental data that were obtained at the FEL in Hamburg - FLASH. © 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen

Untersuchung der photoinduzierten Dynamik in Clustern sowie Pulslängenbestimmung am FEL mittels THz-Lichtfeld-Streaking

Freie-Elektronen-Laser (FEL) stellen femtosekundenlange, hochintensive und kohärente Lichtpulse im XUV- und Röntgenbereich zur Verfügung. Sie ermöglichen dadurch einen Zugang zu einem zuvor unerschlossenen Parameterbereich innerhalb der Röntgenphysik und erlauben es, die Struktur und Dynamik von Materie auf natürlichen Zeit- und Längenskalen zu untersuchen. Nanometergroße Teilchen, wie Edelgascluster, werden während der Belichtung mit hochintensiven FEL-Pulsen in ein hochangeregtes Plasma umgewandelt. Im Folge von weiteren sekundären Prozessen kann das Nanoplasma weiter erhitzt werden. Anschließend zerfallen die Nanoteilchen in die einzelnen geladenen Fragmente. Die Zeitskala für komplexe Elektronen- und Ionendynamik erstreckt sich von wenigen Femto- bis hin zu mehreren Hundert von Pikosekunden. Die Prozesse in Nanoteilchen, die nach der FEL-Anregung stattfinden, sind für konventionelle Pump-Probe Experimente zugänglich. Der experimentelle Zugang zu den Prozessen, die auf der Zeitskala des FEL-Pulses stattfinden, ist dagegen äußerst schwer zu realisieren. Die Technik des Lichtfeld-Streakings ist sensitiv auf den Zeitpunkt der Elektronenemission. Sie ist eine in der Attosekunden- Physik etablierte Technik und eignet sich sowohl zur Charakterisierung von ultrakurzen XUV-Pulsen als auch zur Untersuchung der komplexen Elektronendynamik in Atomen, Molekülen und Nanoteilchen. Im Rahmen der hier vorgestellten Arbeit wird die Elektronenemission von Edelgasclustern mittels Lichtfeld-Streaking mit dem Ziel untersucht, die komplexe Elektronendynamik in Clustern direkt in der Zeitdomäne zugänglich zu machen. In einer der Untersuchungen wurde beobachtet, dass die Ionisation von Clustern erheblich schneller abläuft als von Atomen. In einer weiteren Untersuchung wurde eine neue, vorher nicht beobachtete Linie im Photoelektronenspektrum von heterogenen Xe/Ar-Mischclustern identifiziert. Die Linie wurde korrelierten Elektronenprozessen in den schon expandierten Clustern zugeordnet. Darüber hinaus wird in der vorgelegten Arbeit die Anwendbarkeit des Lichtfeld-Streakings zur Bestimmung der Längen von FEL-Pulsen mit komplexer Pulsstruktur untersucht. Hierfür wurde eine Auswahl an Methoden getroffen, die es ermöglichen, anhand von wenigen simultan gemessenen Spektren, eine zuverlässige Aussage über die Länge der FEL-Pulse zu treffen. Die Zuverlässigkeit der drei in der Arbeit vorgestellten Methoden, wurde an simulierten Streaking-Spektren und an experimentell gewonnenen Streaking-Spektren charakterisiert. Es wurde die Genauigkeit der jeweiligen Methoden zur Bestimmung der Pulslängen im Einzelschuss sowie im Mittel analysiert. Die Ergebnisse dieser Arbeit tragen dazu bei, die Technik des Lichtfeld-Streakings zur zeitaufgelösten Untersuchung hoch angeregter Proben mit komplexer Dynamik zu etablieren und die Entwicklung effizienterer Pulsdiagnostik im XUV- und Röntgenbereich voranzutreiben.Free-electron lasers (FELs) provide femtosecond long and coherent light pulses of high intensity in the XUV and X-ray regime. They thereby provide access to a previously unexplored parameter range within X-ray physics and enable studies of the structure and dynamics of matter on natural time and length scales. Nanometer-sized particles, such as rare gas clusters, are transformed into a highly excited plasma upon exposure to high-intensity FEL pulses. As a result of secondary processes, the nanoplasma might be further heated. Subsequently, the nanoparticles decay into charged fragments. The time scale for complex electron and ion dynamics stretches from a few femtoseconds to several hundreds of picoseconds. The processes in nanoparticles that take place after FEL excitation are accessible for conventional pump-probe experiments. Experimental access to the processes that take place on the time scale of the FEL pulse, however, is extremely difficult to realize. The technique of light- field streaking is sensitive to the instance of the electron emission. This technique is well established in attosecond physics and is suitable both for the characterization of ultrashort XUV pulses and for the investigation of the complex electron dynamics in atoms, molecules and nanoparticles. In the context of this thesis, the electron emission of rare gas clusters is investigated by means of light fi eld streaking with the aim to provide a measurement of the complex electron dynamics in clusters in the time domain. In one of the investigations it was observed that the ionization of clusters proceeds considerably faster than the ionization of atoms. In another investigation a new, previously unobserved line in the photoelectron spectrum of heterogeneous Xe/Ar mixed clusters was identi ed. The line was assigned to correlated electronic processes in the already expanded clusters. Furthermore, the presented thesis investigates the feasibility of light field streaking to retrieve the lengths of FEL pulses with complex pulse structure. For this purpose, a selection of methods was made which allow a reliable estimation of the length of the FEL pulses to be made on the basis of a limited number of simultaneously measured spectra. The reliability of the three presented methods was characterized by simulated streaking spectra as well as by experimentally obtained streaking spectra. The accuracy of the respective methods for the estimation of the pulse lengths was analyzed in single shot mode as well as on average. The results of this work contribute to the development of the technique of light field streaking for time-resolved investigations of highly excited samples with complex dynamics and to the development of efficient single-shot pulse diagnostics in the XUV and X-ray regime

Motivating Factors for Implementing Apparel Certification Schemes—A Sustainable Supply Chain Management Perspective

The motivations for clothing companies to implement dedicated certification schemes as sustainability practices has received limited attention in sustainable supply chain management (SSCM) research so far. Therefore, it is important to understand how different rationales for the implementation of certification schemes have developed in the past because they considerably influence the overall success of sustainability management efforts. This paper picks up on this gap and presents the results of an in-depth comparative case study drawing on interviews conducted with five managers of three companies from the clothing sector in 2018 and abductive content analysis. By applying such a qualitative approach, this study explores motivations and benefits as well as elaborates on the implementation of certification schemes in apparel supply chains. It outlines that certification in the clothing sector is driven by strategic factors, marketing considerations, and information considering sustainability aspects. The study also shows that certification schemes may strengthen the marketing and competitive position of clothing companies as well as sustainability awareness in textile and apparel supply chains in general. Finally, a framework conceptualized from the findings of the interviews presents relevant SSCM practices in the clothing industry. Therefore, the present study contributes to theory building in SSCM by confirming and extending previous research on the implementation of certification schemes for sustainability, as well as to practice by examining reasons to apply certification schemes and potential performance outcomes

Autoionization following nanoplasma formation in atomic and molecular clusters

Nanoplasmas resulting from the ionization of nano-scale particles by intense laser pulses are typically described by quasiclassical models, where electron emission is understood to take place via thermal processes. Recently, we discovered that, following the interaction of intense near-infrared (NIR) laser pulses with molecular oxygen clusters, electron emission from nanoplasmas can also occur from atomic bound states via autoionization [Schütte et al., Phys. Rev. Lett. 114, 123002 (2015)]. Here we extend these studies and demonstrate that the formation and decay of doubly-excited atoms and ions is a very common phenomenon in nanoplasmas. We report on the observation of autoionization involving spin-orbit excited states in molecular oxygen and carbon dioxide clusters as well as in atomic krypton and xenon clusters ionized by intense NIR pulses, for which we find clear bound-state signatures in the electron kinetic energy spectra. By applying terahertz (THz) streaking, we show that the observed autoionization processes take place on a picosecond to nanosecond timescale after the interaction of the NIR laser pulse with the clusters

Mapping ultrafast ionization of atoms and clusters with terahertz-streaking delay

We apply THz-field streaking to temporally resolve the ultrafast ionization of neutral cluster vs atomic targets exposed to intense ultrashort soft x-ray pulses from a free-electron laser (FEL). In the experiment pristine Xe and mixed Xe/Ar clusters as well as Xe atoms are ionized in the vicinity of the $4d→ɛf$ giant resonance of Xe. We compare the relative streaking delay between the center-of-mass oscillations of electrons that have final kinetic energies in the spectral region of the Xe($4d$) photoline. Our results show that clusters are ionized at the beginning of the 100 fs FEL pulse as supported by calculations of target frustration in the focal volume. We have identified a significantly larger 40 fs relative streaking delay between mixed Xe-Ar clusters vs Xe atoms compared to a 15 fs relative delay found for pristine Xe clusters. This is attributed to the high sensitivity of our spectroscopic measurement to the degree of condensation of the cluster target. Our results show that THz streaking is a powerful technique to temporally study electron emission from extended targets under intense FEL radiation on time scales that are significantly shorter than the FEL pulse duration