No description available.

This work presents a joint theoretical and experimental investigation of the electronic structure of quasi one-dimensional cuprates and vanadates. Electron energy-loss spectroscopy in transmission was employed to measure the momentum-dependent loss function of Li2CuO2, CuGeO3, V2O5 and NaV2O5. The comparison between the experimental data and the results from bandstructure as well as cluster calculations allows an explanation of the mobility and correlations of the electrons in these systems. The investigation of the electronic structure of the structurally related cuprates Li2CuO2 and CuGeO3 is exemplary for the study of the transition from a quasi zero-dimensional to a quasi one-dimensional system. In contrast to Li2CuO2 where the electron transitions are strongly localized, the excited states in CuGeO3 can be assigned to the electron hopping to the nearest-neighboured CuO4 plaquettes. The shift of spectral weight from the high energy to the low energy region with increasing coupling between the plaquettes, observed in edge-sharing CuO2 chains, is confirmed by the applied cluster modell. The momentum dependent loss functions of NaV2O5 deliver information about the mobility and correlations of electrons in a quarter-filled ladder system which determine the transition from the charge ordered state into the unordered state at 34 K. Thcontributions of the 3d electrons to the EELS spectra of NaV2O5 are filtered by comparing these spectra with the loss functions of the structurally related V2O5 (d0 configuration). For NaV2O5 the picture of linear chains of V-O-V rungs containing a single d electron in a molecular orbital-like state is confirmed. The comparison of the experimentally determined optical conductivities and those derived from the bandstructrure calculations yield a good agreement upon adoption of an on-site Coulomb interaction U = 2-3 eV. In contrast to the strongly anisotropic hopping within the ladder plane the intersite Coulomb interactions V are about the same size. These interactions are the driving force for the transition from an unordered state at room temperature into a zigzag ordered state observed at low temperatures. / In einer Kombination aus experimentellen und theoretischen Methoden wurden in dieser Arbeit die Elektronenstrukturen von quasi-eindimensionalen Kupraten und Vanadaten untersucht. Dazu wurde die impulsabhängige Verlustfunktion mit Hilfe der Elektronen-Energieverlustspektroskopie in Transmission an Einkristallen von Li2CuO2, CuGeO3, V2O5 und NaV2O5 gemessen. Der Vergleich der experimentellen Daten mit Ergebnissen aus Bandstruktur- und Cluster-Rechnungen erlaubte Rückschlüsse auf die Beweglichkeit und Korrelationen der Elektronen in diesen Systemen. Die Untersuchung der elektronischen Anregungen in den strukturell sehr ähnlichen Kupraten Li2CuO2 und CuGeO3 ist beispielhaft für das Studium des Übergangs von einem quasi-nulldimensionalen zu einem quasi-eindimensionalen System. In Li2CuO2 finden die elektronischen Übergänge vorwiegend lokal auf der CuO4-Plakette statt. Dagegen findet man in CuGeO3 angeregte Zustände, die als das Hüpfen der Elektronen auf benachbarte Plaketten interpretiert werden können. Das angewandte Cluster-Modell bestätigt für eine zunehmende Kopplung zwischen den Plaketten die in eckenverbundenen Kupratketten beobachtete Verschiebung des spektralen Gewichts vom hoch- zum niederenergetischen Bereich. Die Verlustfunktionen von NaV2O5 liefern wertvolle Informationen über die Freiheitsgrade und Korrelationen der Elektronen in einem viertelgefüllten Leitersystem, die wesentlich den Phasenübergang zwischen geordneter und ungeordneter Ladung bei 34 K bestimmen. Die Beiträge der 3d-Elektronen von NaV2O5 zu den EELS-Spektren konnten durch eine vergleichende Studie der Verlustfunktionen des strukturell verwandten V2O5, das keine d-Elektronen besitzt, separiert werden. Die Beschreibbarkeit der Elektronenstruktur in NaV2O5 durch ein effektives Modell einfach besetzter, molekülähnlicher V-O-V-Sprossen wird bestätigt. Die Coulomb-Wechselwirkung U kann in diesem Modell auf den Wertebereich zwischen 2 und 3 eV eingeschränkt werden. Im Gegensatz zu den stark anisotropen Hüpfwahrscheinlichkeiten in der Leiterebene sind die Coulomb-Wechselwirkungen V zwischen Elektronen auf benachbarten Vanadiumplätzen nahezu von gleicher Größe. Diese Wechselwirkungen sind die treibende Kraft für den Übergang von einem ungeordneten Zustand bei Raumtemperatur in einen zickzackgeordneten Grundzustand bei tiefen Temperaturen.

Darmstadt, Techn. Universiẗat, Diss., 2008. / Dateien im PDF-Format.

Strongly correlated systems on geometrically frustrated lattices can stabilize a large number of interesting phases that includes a wide array of novel Mott insulators in both bosonic and electronic systems. Charge fluctuations in a Mott insulator are suppressed due to strong mutual interaction among the particles. The presence of frustration is of particular importance as the physics it offers is often rich, unexpectedly complicated, and continues to raise many open questions. The thesis elucidates some of these issues on a kagome lattice where strong interactions among the particles in the Mott phase impose non-trivial local constraints depending on the filling fraction on the lattice. These Mott insulators, in addition to featuring unusual magnetic and/or charge ordering, can also harbor topologically ordered states of quantum matter, e.g., resonating valence bond liquids realized in certain quantum dimer models on non-bipartite lattices. The dimer models can be regarded as low-energy effective theories for different types of bosonic models in the strong-coupling limit. Exploring this connection is a central theme of this thesis with the aim of realizing novel strongly correlated ground states. Past studies of these models have revealed the existence of various ordered and disordered phases with distinct signatures. Among these low-energy phases, the presence of a stable topological liquid at a particular point, known as Rokhsar-Kivelson point, in the phase diagram is notable. The classical versions of the dimer model are also known to have garnered a vast interest in various fields ranging from problems of pure mathematical origin to ones in physical chemistry as well as statistical physics. Pioneered by Kasteleyn, several analytical works came forward to exactly calculate the partition function of the problem from which other physical observables can be derived. Classical numerical methods are extensively applied to these models to verify the analytical predictions. We introduce a new classical algorithm here to compute the correlation functions of a classical dimer model on a square (bipartite) and a triangular (non-bipartite) lattice based on a tensor network construction. The method, called tensor network renormalization group, turns out to be a powerful tool for simulating short-ranged gapped systems as inferred from our results benchmarked against the classical Monte-Carlo technique and compared with past analytical studies. One should note that the quantum dimer model at the Rokhsar-Kivelson point can also be described as an infinite temperature canonical ensemble of classical dimers because of the particular structure of the ground state which is an equal weight superposition in the configuration manifold. The geometry of the lattice plays a pivotal role in deciding the nature of the phases that arise in the dimer models. Many physical properties of the dimer liquid phase can be extracted in the simple classical setting which certainly allows for a deep understanding of the classical models to be developed. The liquid phase is gapped on non-bipartite lattices and gapless on bipartite lattices, which is reflected in the decay of correlation functions with spatial distances. In general on non-bipartite lattices, the topological nature of the dimer liquid is characterized by a Z2 topological order which survives even when the model is perturbed away from the Rokhsar-Kivelson point. Stability of this liquid phase not only depends on the lattice geometries but notably on dimer concentrations also. In this context, we focus on a particular variant of the dimer model on a triangular lattice which is known as the quantum fully packed loop model. The model is composed of nonintersecting closed loops made of dimers and governed by the same Hamiltonian as the quantum dimer model. The loop model provides an effective low-energy description of a strongly correlated bosonic system at 1/3 filling on the kagome lattice. The corresponding Bose-Hubbard Hamiltonian consists of nearest-neighbor hopping and all possible repulsive interactions within a hexagonal plaquette. Conspicuous features of the zero-temperature phase diagram for this model include (i) presence of a stable Z2 liquid even without any Rokhsar-Kivelson potential term (in distinction to the standard quantum dimer model), and (ii) an unconventional phase transition from the liquid phase to a novel crystalline phase that has nematic order (dubbed lattice nematic). For a deeper understanding of the physics, a mapping to an Ising gauge theory is presented. The gauge theoretic description provides a useful way to predict the nature of the quantum phase transition to lie in the O(3) universality class. Finally a fermionic model at the same 1/3 filling is considered in which the ground state exhibits a number of exotic local orderings resulting from the spin-charge interplay of electrons. The Hamiltonian comprises nearest-neighbor hopping, strong on-site Coulomb interaction, and repulsive interaction terms only between nearest-neighbors. In the strong correlation limit, this fermionic problem maps to a two-color fully packed loop model – a model in which the loop segments carry an additional quantum number as color on a honeycomb lattice. The effective theory is governed by coherent three-particle ring exchanges and nearest-neighbor antiferromagnetic spin exchanges. The competition between these two leads to a phase diagram composed of a novel plaquette ordered state (known as the plaquette phase) that undergoes phase transition to a new kind of charge ordered state which we call a short loop phase. From our numerical analysis, we conclude that the plaquette phase features an unusual antiferromagnetic order with gapless spin excitations while the charge-ordered state is subjugated by spin fluctuations of localized electrons arranged in small hexagonal loops on the kagome lattice.

All across physics research, incoherent and coherent light sources are extensively utilized. Especially highly brilliant X-ray sources such as third generation synchrotrons or free-electron lasers have become an invaluable tool enabling experimental techniques that are unique to these kinds of light sources. But these sources have developed to large scale facilities and a demand in compact laboratory scale sources providing radiation of similar quality arises nowadays. This thesis focuses on Traveling-Wave Thomson-Scattering (TWTS) which allows for the realization of ultra-compact, inherently synchronized and highly brilliant light sources. The TWTS geometry provides optical undulators, through which electrons pass and thereby emit radiation, with hundreds to thousands of undulator periods by utilizing pulse-front tilted lasers pulses from high peak-power laser systems. TWTS can realize incoherent radiation sources with orders of magnitude higher photon yield than established head-on Thomson sources. Moreover, optical free-electron lasers (OFELs) can be realized with TWTS if state-of-the-art technology in electron accelerators and laser systems is utilized. Tilting the laser pulse front with respect to the wavefront by half of this interaction angle optimizes electron and laser pulse overlap by compensating the spatial offset between electrons and the laser pulse-front at the beginning of the interaction when the electrons are far from the laser pulse axis. The laser pulse-front tilt ensures continuous overlap between electrons and laser pulse while the electrons cross the laser pulse cross-sectional area. Thus the interaction distance can be controlled in TWTS by the laser pulse width rather than laser pulse duration. Utilizing wide, petawatt class laser pulses allows realizing thousands of optical undulator periods. This thesis will show that TWTS OFELs emitting ultraviolet radiation are realizable today with existing technology for electron accelerators and laser systems. The requirements on electron bunch and laser pulse quality of these ultraviolet TWTS OFELs are discussed in detail as well as the corresponding requirements of TWTS OFELs emitting in the soft and hard X-ray range. These requirements are derived from scaling laws which stem from a self-consistent analytic description of the electron bunch and radiation field dynamics in TWTS OFELs presented within this thesis. It is shown that these dynamics in TWTS OFELs are qualitatively equivalent to the electron bunch and radiation field dynamics of standard free-electron lasers which analytically proves the applicability of TWTS for the realization of an optical free-electron laser. Furthermore, experimental setup strategies to generate the pulse-front tilted TWTS laser pulses are presented and designs of experimental setups for the above examples are discussed. The presented setup strategies provide dispersion compensation, required due to angular dispersion of the laser pulse, which is especially relevant when building compact, high-yield hard X-ray TWTS sources in large interaction angle setups. An example of such an enhanced Thomson source by TWTS, which provides orders of magnitude higher spectral photon density than a comparable head-on interaction geometry, is presented, too

Polypropylene (PP) has excellent mechanical and chemical properties. Thus, it is used in a wide range of applications. However, like for most polymers, the high flammability of PP limits its application in various fields requiring specific flame-retardant standards. Some of halogenated flame retardants are restricted by European Community directives ROHs, WEEE and REACH. Now metallic hydroxides flame retardants are widely used in industry, but the high loading (about 60 wt %) seriously destroys the mechanical properties of polymeric materials. To improve the performance of flame retardant polymers, an environment-friendly electron beam (EB) technology has been successfully used in modifying flame retardant and polymer matrix. In this work, high efficient functional intumescent flame retardants and functional surfactant are designed and prepared for EB technology. In-depth studies the thermal stability, fire behavior and mechanical properties of these flame retardant PP composites have been studied. The possible graft-linking and cross-linking mechanisms of such EB modified composites can be well established. Specially, it is shown that the novel surfactant has better thermal stability in comparison to traditionally used modifiers. Another part of this work deals with the exploration of novel allylamine polyphosphate (AAPP) as flame retardant crosslinker for PP by electron beam (EB) treatment. Multifunctional AAPP showed unique efficient intumescent flame retardant properties. The limiting oxygen index (LOI) value and the effective melt drop resistance in UL-94 test of multifunctional flame retardant PP composites is greatly enhanced. In the cone calorimeter test, a reduction of peak heat release rate, total heat release and smoke production is achieved. Moreover, EB treatment increased the thermal stability of these designed flame retardant PP composites. Furthermore, AAPP provided an excellent quality of char residue in the combustion stage due to P−N−C and P−O−C structure. In addition, synergistic mechanism of AAPP with montmorillonite (MMT) was explored. Finally, different EB parameters have been used to modify fire retardant polymer nanocomposites. The effects of EB treatment on thermal stability, fire behavior and mechanical properties of fire retardant PP nanocomposites have been discussed. The heat release, the production of toxic gases and the mass loss of EB modified fire retardant PP nanocomposites are delayed in accordance to the result of cone calorimeter test. Based on these results high performance fire retardant polymer nanocomposites can be developed for industrial applications such as insulated material of wire, cable, etc.

Es werden die physikalischen Grundlagen zur inelastischen Streuung mittelschneller Elektronen im Hinblick auf die Untersuchung des Energieverlustes beschrieben. Die instrumentellen Grundlagen der Energieverlust-Spektroskopie unter besonderer Berücksichtigung des Einsatzes in Transmissionselektronenmikroskopen werden erläutert. Der Einfluß des erfaßsten Streuwinkelbereichs wird diskutiert. Es werden Möglichkeiten zur Auswertung von Energieverlustmessungen im Bereich der Interbandübergangs- und Plasmonanregungen sowie im Bereich der Anregung von tieferliegenden (Rumpf-)Zuständen angegeben. Zur Anwendung der Elektronen-Energieverlust-Spektroskopie werden einige Beispiele angeführt. Von Messungen an ionengestützt abgeschiedenen Kohlenstoff- und Kohlenstoff-Stickstoff-Schichten werden Aussagen zur elektronischen und atomaren Struktur abgeleitet. Diese Ergebnisse werden unter Berücksichtigung relevanter Strukturmodelle und Abscheideparameter diskutiert. Aus Untersuchungen von Bornitridschichten wird eine vertikale Schichtung von kubischem Bornitrid über hexagonal koordiniertem verifiziert. Die Streuphase des bei der Ionisation des Al-1s-Zustandes entstehenden Sekundärelektrons bei der Rückstreuung an den nächsten Nachbarn wird durch Untersuchung der kantenfernen Feinstruktur bestimmt. Weitere Untersuchungen kantennaher Feinstrukturen an einer amorphen SiCrAl-Schicht sowie an Kohlenstoffschichten werden vorgestellt. Mögliche Einflüsse kovalenter Bindungen auf die Ergebnisse werden dabei diskutiert. Schließlich werden räumlich hochauflösende Energieverlustmessungen vorgestellt, die zum Nachweis etwa 2 nm dicker Vanadiumoxidschichten auf Rutilkristalliten führten.

Die Anwendung von Hochintensitätslasern zur Beschleunigung von Teilchen bietet eine Alternative zu klassischen Teilchenbeschleunigern und den von diesen erzeugten Strahlenqualitäten. Nach großen Fortschritten auf dem Gebiet der Laser-Teilchenbeschleunigung wurde die Anwendung der neuen Technologie in der klinischen Ionentherapie vorgeschlagen und diskutiert. Bevor es dazu kommen kann, muss aber neben der Verbesserung der Strahleigenschaften, wie z. B. der Erhöhung der Energie, und der Stabilität der Teilchenbeschleunigung auch eine geeignete physikalische und dosimetrische Charakterisierung entwickelt und die biologische Wirksamkeit dieser neuartigen, ultrakurz gepulsten Strahlenqualität mit extrem hoher Pulsdosisleistung untersucht werden. Dies erfordert eine ganze Reihe von umfangreichen Experimenten der notwendigen Translationskette, angefangen von in vitro Zellbestrahlungen über in vivo Studien bis hin zu präklinischen Untersuchungen und ersten klinischen Studien. Hierzu wurden das Verbundprojekt onCOOPtics gegründet und in einem ersten Schritt in vitro Zellbestrahlungen zur Untersuchung der biologischen Wirksamkeit laserbeschleunigter Teilchen durchgeführt. Dazu wurden Dosis-Effekt-Kurven für humane Tumor- und Normalgewebs-Zelllinien jeweils für mehrere biologische Endpunkte bestimmt. Begonnen wurde dabei mit der umfangreichen Untersuchung laserbeschleunigter Elektronen am JeTi-Lasersystem in Jena, auf welche zum Zeitpunkt der Verfügbarkeit des DRACO-Lasersystems in Dresden die dosimetrische und strahlenbiologische Charakterisierung laserbeschleunigter Protonen an diesem Lasersystem folgte. Dabei stellte die Entwicklung einer präzisen Dosimetrie zur Bestimmung der applizierten Dosis aufgrund der Strahleigenschaften laserbeschleunigter Teilchen eine große Herausforderung dar. Sie ist aber sowohl im Hinblick auf eine spätere klinische Anwendung als auch für die Durchführung quantitativer strahlenbiologischer Experimente obligatorisch. Diese Arbeit, die im Rahmen des Verbundprojektes entstanden ist, leistet dazu in vielfacher Hinsicht einen wesentlichen Beitrag: Erstens wurden geeignete Detektoren zur präzisen dosimetrischen Charakterisierung laserbeschleunigter Elektronen und Protonen entwickelt, optimiert und charakterisiert sowie präzise kalibriert. So wurden umfangreiche Studien zu verschiedenen Eigenschaften der auch in der klinischen Dosimetrie angewandten radiochromischen Filme durchgeführt und die Filme entsprechend kalibriert. Dabei wurden neue Erkenntnisse u. a. über deren Energieabhängigkeit gewonnen, die für zahlreiche Anwendungen der Filme von Bedeutung sind. Weiterhin wurden verschiedene Ionisationskammern zur Echtzeit-Strahlmonitorierung von laserbeschleunigten Elektronen und Protonen ausgewählt und dosimetrisch charakterisiert. Zudem wurde der Einsatz von CR-39 Festkörperspurdetektoren zur spektroskopischen Untersuchung laserbeschleunigter Protonen etabliert, indem die Nachverarbeitung und Auslesung der Detektoren charakterisiert und optimiert wurden und außerdem eine retrospektive Filterprozedur der detektierten Krater entwickelt und angewendet wurde. Ferner wurde ein Faraday Cup, der auf die speziellen Eigenschaften derzeitiger laserbeschleunigter Protonen-Strahlenqualitäten abgestimmt ist, entwickelt, charakterisiert und mit drei voneinander unabhängigen Methoden kalibriert. Die radiochromischen Filme und der Faraday Cup konnten daraufhin als Referenzdosimeter sowohl an den konventionellen als auch an den neuartigen Laser-Teilchenbeschleunigern erfolgreich eingesetzt werden. Zweitens bildete die durchgeführte Echtzeit- und Referenzdosimetrie laserbeschleunigter Elektronen die Grundlage für die weltweit ersten systematischen Zellbestrahlungsexperimente dieser Strahlenqualität. Dabei konnten trotz großer Pulsdosisschwankungen alle Anforderungen bezüglich Dosishomogenität, Strahlstabilität, präziser Deposition einer vorgegebenen Dosis und Unsicherheit der bestimmten applizierten Dosis, die für eine quantitative Auswertung der radiobiologischen Daten notwendig sind, erfüllt werden. Exemplarisch sei die bestimmte Gesamt-Dosisunsicherheit von unter 10% genannt. Drittens wurden auch laserbeschleunigte Protonen so präzise dosimetrisch monitoriert und charakterisiert, dass auch mit dieser Strahlenqualität quantitative strahlenbiologische Untersuchungen durchgeführt werden konnten. Herausgefordert durch die kurze Reichweite der Protonen im Submillimeterbereich und das breite Energiespektrum dieser Strahlenqualität, gelang dies neben der Charakterisierung und Kalibrierung der einzelnen Detektoren durch die Konzeption und Realisierung eines integrierten Dosimetrie- und Zellbestrahlungssystems (IDOCIS).Weltweit erstmalig wurde eine Echtzeit-Strahlmonitorierung während der Zellbestrahlungen mit laserbeschleunigten Protonen durchgeführt, die sowohl zur kontrollierten Applikation einer vorgegebenen Dosis und zur Strahlüberwachung als auch zusammen mit der durchgeführten Referenzdosimetrie zur hochpräzisen Bestimmung der absolut in den Zellen deponierten Dosis diente. Außerdem trug die parallele und redundante Verwendung zweier voneinander unabhängiger Referenzdosimetrie-Systeme erheblich zur Erreichung einer hohen Zuverlässigkeit und Sicherheit bei. Die Unsicherheit in der bestimmten deponierten Dosis betrug entsprechend für den Endpunkt der residualen DNS-Doppelstrangbrüche 24h nach Bestrahlung, für den eine vollständige Dosis-Effekt-Kurve ermittelt wurde, nur ca. 10%. Die Unsicherheit liegt damit schon fast in dem Bereich, der an klinisch angewandten Beschleunigern zulässig ist (3-5%). Dagegen konnte zu Beginn dieser Arbeit die Dosis laserbeschleunigter Protonen nur mit einer Ungenauigkeit von mehr als 50% abgeschätzt werden. Viertens wurden die zur Bestimmung der relativen biologischen Wirksamkeit notwendigen Vergleichsbestrahlungen mit konventionellen Elektronen- und Protonenstrahlenquellen und die zur Vergleichbarkeit der konventionellen und laserbeschleunigten Strahlenqualitäten erforderlichen Referenzbestrahlungen mit 200kVp Röntgenröhren im Rahmen dieser Arbeit ebenfalls dosimetrisch optimiert und genau charakterisiert. Die dosimetrischen Ergebnisse der vorliegenden Arbeit waren eine notwendige Voraussetzung für die im Rahmen anderer Arbeiten vollzogene strahlenbiologische Auswertung der durchgeführten Zellbestrahlungen. Dabei wurde insgesamt kein signifikanter Unterschied in der strahlenbiologischen Wirksamkeit zwischen laserbeschleunigten, ultrakurz gepulsten und konventionellen, kontinuierlichen Strahlenqualitäten weder für Elektronen noch für Protonen festgestellt. Durch die Konsistenz dieser Ergebnisse für beide Teilchenarten und unterschiedliche biologische Endpunkte ist damit die nächste Stufe auf dem translationalen Weg hin zur klinischen Anwendung laserbeschleunigter Teilchen begehbar: Die Durchführung von in vivo Untersuchungen. Dabei muss zwar von einer zweidimensionalen (Zell-Monolayer) auf eine dreidimensionale Zielvolumenbestrahlung (Tumor) übergegangen werden, wobei aber die im Rahmen der vorliegenden Arbeit entwickelten Dosimetrieverfahren und Detektoren auch bei den Tierbestrahlungen angewendet und eingesetzt werden können. / The application of high-intensity lasers for particle acceleration provides an alternative to conventional particle accelerators and also alternative beam qualities. Soon after the recent progress in the field of laser particle acceleration, its application in clinical ion therapy was proposed and discussed widely. Besides the improvement of the beam properties (increasing of beam energy and stability of particle acceleration process, e. g.) a capable physical and dosimetric characterization has to be developed before the technology can be applied in cancer therapy. The same is true for investigation of the biological effectiveness of this new, ultra-short pulsed beam quality with extremely high pulse dose rate. Hence, the whole translational chain, beginning from in vitro cell irradiation over in vivo studies to the point of preclinical investigations and first clinical trials, is necessary. For this reason, in a first step the joint research project onCOOPtics was founded and in vitro cell irradiation experiments were performed to study the biological effectiveness of laser accelerated particles. Therefore, dose-effect-curves for tumor and normal tissue cell lines were determined for different biological endpoints. Starting with extensive experiments with laser accelerated electrons at the JeTi laser system in Jena, the investigations were continued with dosimetric and radiobiological characterization of laser accelerated protons at the DRACO laser system in Dresden shortly after the DRACO laser started its operation. In this process, the development of a precise dosimetry for determination of the applied dose posed a great challenge due to the beam properties of laser accelerated particles. However, this is a crucial and compulsive requirement for both, the future clinical application and also for the realization of quantitative radiobiological experiments. Compiled in the onCOOPtics framework, this paper contributed to this task in multiple key aspects: Firstly, capable detectors for precise dosimetric characterization of laser accelerated electrons and protons were developed, optimized and characterized as well as precisely calibrated. Thus, comprehensive investigations were performed studying different properties of radiochromic films which are also applied in clinical dosimetry. In addition, these films were precisely calibrated for different beam qualities. Thereby, new findings of the energy dependence of radiochromic films were obtained which are of importance for numerous applications of these films. Moreover, different ionization chambers for real-time beam monitoring of laser accelerated electrons and protons were selected and characterized. Furthermore, the application of CR-39 solid state track detectors was established for spectroscopic investigations of laser accelerated protons by characterizing and optimizing the postirradiation processing and the readout of the detectors. Also a retrospective filter procedure of the detected tracks was developed and applied. Moreover, a Faraday Cup adjusted to the special properties of current laser accelerated proton beam qualities was developed, characterized and precisely calibrated by means of three independent calibration methods. Finally, the radiochromic films and the Faraday Cup could be used as reference dosimeters both for conventional accelerators and also for novel laser particle accelerators. Secondly, the performed real-time and reference dosimetry of laser accelerated electrons was the prerequisite of the first systematic cell irradiation experiments with this beam quality worldwide. Despite high pulse dose fluctuations, all requirements were satisfied concerning dose homogeneity, beam stability, precise deposition of a prescribed dose and uncertainty of the applied dose, that are all necessary for a quantitative evaluation of the radiobiological data. Exemplary, a total dose uncertainty below 10% was reached. Thirdly, laser accelerated protons were precisely monitored and characterized allowing quantitative, well-founded radiobiological investigations with this beam quality. This task was very much challenged by the short range of the protons in the sub-millimeter range and the broad energy spectrum of the beam quality. It was succeeded not only due to the comprehensive characterization and precise calibration of the different detectors but also due to the conception and realization of an integrated dosimetry and cell irradiation system (IDOCIS). For the first time, a real-time beam monitoring during cell irradiation with laser accelerated protons was performed. This real-time monitoring was not only used for controlled application of the prescribed dose and beam monitoring and also – together with the performed reference dosimetry – for precise determination of the deposited dose at cell location. In addition, high reliability and safety was considerably ensured by using two independent reference dosimetry systems in parallel. Hence, the determined uncertainty of the deposited dose was only about 10% for the biological endpoint of the residual DNA double strand breaks 24h after irradiation. For this endpoint a complete dose-effect-curve was obtained. Therefore, the achieved uncertainty is almost as small as necessary at clinically applied accelerators (3

All across physics research, incoherent and coherent light sources are extensively utilized. Especially highly brilliant X-ray sources such as third generation synchrotrons or free-electron lasers have become an invaluable tool enabling experimental techniques that are unique to these kinds of light sources. But these sources have developed to large scale facilities and a demand in compact laboratory scale sources providing radiation of similar quality arises nowadays. This thesis focuses on Traveling-Wave Thomson-Scattering (TWTS) which allows for the realization of ultra-compact, inherently synchronized and highly brilliant light sources. The TWTS geometry provides optical undulators, through which electrons pass and thereby emit radiation, with hundreds to thousands of undulator periods by utilizing pulse-front tilted lasers pulses from high peak-power laser systems. TWTS can realize incoherent radiation sources with orders of magnitude higher photon yield than established head-on Thomson sources. Moreover, optical free-electron lasers (OFELs) can be realized with TWTS if state-of-the-art technology in electron accelerators and laser systems is utilized. Tilting the laser pulse front with respect to the wavefront by half of this interaction angle optimizes electron and laser pulse overlap by compensating the spatial offset between electrons and the laser pulse-front at the beginning of the interaction when the electrons are far from the laser pulse axis. The laser pulse-front tilt ensures continuous overlap between electrons and laser pulse while the electrons cross the laser pulse cross-sectional area. Thus the interaction distance can be controlled in TWTS by the laser pulse width rather than laser pulse duration. Utilizing wide, petawatt class laser pulses allows realizing thousands of optical undulator periods. This thesis will show that TWTS OFELs emitting ultraviolet radiation are realizable today with existing technology for electron accelerators and laser systems. The requirements on electron bunch and laser pulse quality of these ultraviolet TWTS OFELs are discussed in detail as well as the corresponding requirements of TWTS OFELs emitting in the soft and hard X-ray range. These requirements are derived from scaling laws which stem from a self-consistent analytic description of the electron bunch and radiation field dynamics in TWTS OFELs presented within this thesis. It is shown that these dynamics in TWTS OFELs are qualitatively equivalent to the electron bunch and radiation field dynamics of standard free-electron lasers which analytically proves the applicability of TWTS for the realization of an optical free-electron laser. Furthermore, experimental setup strategies to generate the pulse-front tilted TWTS laser pulses are presented and designs of experimental setups for the above examples are discussed. The presented setup strategies provide dispersion compensation, required due to angular dispersion of the laser pulse, which is especially relevant when building compact, high-yield hard X-ray TWTS sources in large interaction angle setups. An example of such an enhanced Thomson source by TWTS, which provides orders of magnitude higher spectral photon density than a comparable head-on interaction geometry, is presented, too

In this thesis we study a variety of two- and three-dimensional (2D and 3D, respectively) nodal semimetals, subjected to local electronic interactions or disorder. Such systems constitute a minimal model for various real materials and capture a plethora of interesting physical phenomena therein. Our methodology includes an unbiased renormalization group analysis controlled by epsilon expansions about the appropriate lower critical dimension, mean-field analysis, as well as complementary numerical analyses. First, we focus on emergent symmetries at various infrared unstable quantum critical points, appearing in a renormalization group flow of interaction couplings. We investigate a 3D chiral Dirac semimetal, which in a noninteracting system enjoys a microscopic U(1)⊗SU(2) global symmetry. Though the chiral symmetry is absent in the interacting model, it gets restored (partially or fully) at various fixed points as emergent phenomena. Subsequently, we study a collection of 3D interacting effective spin-3/2 biquadratic Luttinger fermions, and demonstrate the emergence of full rotational symmetry between the distinct nematic sectors (namely Eg and T2g ) of the corresponding octahedral group. We then investigate the effects of electronic interactions at zero and finite temperature and chemical doping in a collection of (i) 2D Dirac and Luttinger fermions, constituting the linearly and quadratically dispersing low-energy excitations in monolayer and bilayer graphene, respectively, and (ii) 3D Luttinger fermions, describing a biquadratic touching of Kramers degenerate conduction and valence bands, relevant in the normal state of 227 pyrochlore iridates, and half-Heusler compounds, for example. These systems exhibit a plethora of competing broken symmetry phases (both magnetic and superconducting) when tuning the strength of interactions, temperature, and chemical doping. In this context we propose the selection rules, identifying the broken symmetry phases promoted by a given interaction channel, and the organizing principle, ordering these preselected phases along the temperature axis based on a generalized energy-entropy argument. Finally, we explore topological aspects of nodal Fermi liquids. We propose an experimentally feasible way to engineer higher-order topological phases via the application of uniaxial strain on a 3D Luttinger semimetal. Favoring a direction, strain explicitly breaks cubic symmetry. We show that the corresponding nematic orderings of Luttinger fermions result in a topological insulator or Dirac semimetal, depending on the sign (compressive or tensile, respectively) of the strain. We show that both of these phases host 1D hinge modes, localized along the edges parallel to the direction of strain, that are therefore second-order topological in nature. We then investigate the effects of disorder on such a second-order Dirac semimetal, and show its stability for weak enough disorder. At a critical disorder strength the system goes through a quantum phase transition into a diffusive metal phase and the toplogical hinge states melt into the bulk. The methodology presented in this thesis can be extended to a large family of correlated multiband systems, such as Weyl and nodal-loop semimetal.