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Luftverkehrsdienste benötigen ergänzende boden- und luftseitige Infrastrukturen. Kapazitätsbeschränkungen des Start- und Landebahnsystems eines Flughafens stellen einen erheblichen Engpass dar. Das Nutzungsrecht hängt von der Verfügbarkeit eines Slots ab. Wenn die Nachfrage nach Slots das Angebot übersteigt, ist ein Zuweisungsverfahren erforderlich. In den meisten Ländern der Welt gibt es dafür keinen Marktmechanismus. Eine Besitzstandsklausel beschränkt den Zutritt für Neueinsteiger auf überlasteten Flughäfen. Aus der Perspektive der Eigentumsrechte lässt sich Abhilfe schaffen. Air transport services require complementary ground and air infrastructure. Capacity constraints of an airport's runway system create a significant bottleneck. The right of use depends on the availability of a slot. When the demand for slots exceeds the supply, an allocation process is required. In most countries of the world, there is no market mechanism for this. A grandfather clause restricts entry for new entrants at congested airports. A remedy can be found in a property rights perspective.

In recent years, much research has been undertaken to investigate the suitability of two-dimensional materials to act as single-photon sources with high optical and quantum optical quality. Amongst them, transition-metal dichalcogenides, especially WSe$_{2}$, have been one of the subjects of intensive studies. Yet, their single-photon purity and photon indistinguishability, remain the most significant challenges to compete with mature semiconducting systems such as self-assembled InGaAs quantum dots. In this work, we explore the emission properties of quantum emitters in a WSe$_{2}$ monolayer which are induced by metallic nanoparticles. Under quasi-resonant pulsed excitation, we verify clean single-photon emission with a $g^{(2)}(0) = 0.036\pm0.004$. Furthermore, we determine its temperature dependent coherence time via Michelson interferometry, where a value of (13.5$\pm$1.0) ps is extracted for the zero-phonon line (ZPL) at 4 K, which reduces to (9$\pm$2) ps at 8 K. Associated time-resolved photoluminescence experiments reveal a decrease of the decay time from (2.4$\pm$0.1) ns to (0.42$\pm$0.05) ns. This change in decay time is explained by a model which considers a F\"orster-type resonant energy transfer process, which yields a strong temperature induced energy loss from the SPE to the nearby Ag nanoparticle.

We present a self-consistent Maxwell-Bloch theory to analytically study the interaction between a nanostructure consisting of a metal nanoparticle and a monolayer of transition metal dichalcogenide. For the combined system, we identify an effective eigenvalue equation that governs the center-of-mass motion of the dressed excitons in a plasmon-induced potential. Examination of the dynamical equation of the exciton-plasmon hybrid reveals the existence of bound states with negative eigenenergies, which we interpret as excitons localized in the plasmon-induced potential. The appearance of these bound states in the potential indicates strong coupling between excitons and plasmons. We quantify this coupling regime by computing the scattered light in the near-field explicitly and identify signatures of strong exciton-plasmon coupling with an avoided crossing behavior and an effective Rabi splitting of tens of meV., Comment: 16 pages, 13 figures

We report on the spatial coherence of interlayer exciton ensembles as formed in MoSe$_2$/WSe$_2$ heterostructures and characterized by point-inversion Michelson-Morley interferometry. Below 10 K, the measured spatial coherence length of the interlayer excitons reaches values equivalent to the lateral expansion of the exciton ensembles. In this regime, the light emission of the excitons turns out to be homogeneously broadened in energy with a high temporal coherence. At higher temperatures, both the spatial coherence length and the temporal coherence time decrease, most likely because of thermal processes. The presented findings point towards a spatially extended, coherent many-body state of interlayer excitons at low temperature.

The interplay of the non-equivalent corners in the Brillouin zone of transition metal dichalcogenides have been investigated extensively. While experimental and theoretical works contributed to a detailed understanding of the relaxation of selective optical excitations and the related relaxation rates, only limited microscopic descriptions of stationary experiments are available so far. In this manuscript we present microscopic calculations for the non-equilibrium steady state properties of excitons during continuous wave pumping. We find sharp features in photoluminescence excitation spectra and degree of polarization which result from phonon assisted excitonic transitions dominating over exciton recombination and intervalley exchange coupling.

Low-temperature photoluminescence (PL) of hBN-encapsulated monolayer tungsten diselenide (WSe$_2$) shows a multitude of sharp emission peaks below the bright exciton. Some of them have been recently identified as phonon sidebands of momentum-dark states. However, the exciton dynamics behind the emergence of these sidebands has not been revealed yet. In this joint theory-experiment study, we theoretically predict and experimentally observe time-resolved PL providing microscopic insights into thermalization of hot excitons formed after optical excitation. In good agreement between theory and experiment, we demonstrate a spectral red-shift of phonon sidebands on a timescale of tens of picoseconds reflecting the phonon-driven thermalization of hot excitons in momentum-dark states. Furthermore, we predict the emergence of a transient phonon sideband that vanishes in the stationary PL. The obtained microscopic insights are applicable to a broad class of 2D materials with multiple exciton valleys., Comment: 10 pages, 5 figures

Understanding the ultrafast coupling and relaxation mechanisms between valleys in transition metal dichalcogenide semiconductors is of crucial interest for future valleytronic devices. Recent ultrafast pump-probe experiments showed an unintuitive significant bleaching at the excitonic $B$ transition after optical excitation of the energetically lower excitonic $A$ transition. Here, we present a possible microscopic explanation for this surprising effect. It is based on the joint action of exchange coupling and phonon-mediated thermalization into dark exciton states and does not involve a population of the B exciton. Our work demonstrates how intra- and intervalley coupling on a femtosecond timescale governs the optical valley response of 2D semiconductors.

We investigate the impact of optically induced F��rster coupling in van der Waals heterostructures consisting of graphene and a monolayer transition metal dichalcogenide (TMD). In particular, we predict the corresponding dephasing rates and a fast energy transfer between the TMD layer and graphene being in the picosecond range. Exemplary we find a transition rate of thermalized excitons of about 4 ps$^{-1}$ in a MoSe$_2$-graphene stack at room temperature. This timescale is in good agreement with the recently measured exciton lifetime in this heterostructure.

We describe an efficient near-field to far-field transformation for optical quasinormal modes, which are the dissipative modes of open cavities and plasmonic resonators with complex eigenfrequencies. As an application of the theory, we show how one can compute the reservoir modes (or regularized quasinormal modes) outside the resonator, which are essential to use in both classical and quantum optics. We subsequently demonstrate how to efficiently compute the quantum optical parameters necessary in the theory of quantized quasinormal modes [Franke et al., Phys. Rev. Lett. 122, 213901 (2019)]. To confirm the accuracy of our technique, we directly compare with a Dyson equation approach currently used in the literature (in regimes where this is possible), and demonstrate several order of magnitude improvement for the calculation run times. We also introduce an efficient pole approximation for computing the quantized quasinormal mode parameters, since they require an integration over a range of frequencies. Using this approach, we show how to compute regularized quasinormal modes and quantum optical parameters for a full 3D metal dimer in under one minute on a standard desktop computer. Our technique is exemplified by studying the quasinormal modes of metal dimers and a hybrid structure consisting of a gold dimer on top of a photonic crystal beam. In the latter example, we show how to compute the quantum optical parameters that describe a pronounced Fano resonance, using structural geometries that cannot practically be solved using a Dyson equation approach. All calculations for the spontaneous emission rates are confirmed with full-dipole calculations in Maxwell's equations and are shown to be in excellent agreement.

Dienstleistungen im Luftverkehr werden entlang einer vertikal disaggregierten Wertschöpfungskette von spezialisierten Anbietern erbracht. Vom Luftverkehr gehen regional- und gesamtwirtschaftliche Impulse aus. Ihre Erfassung erweist sich allerdings als schwierig. Gleiches gilt für die negativen Externalitäten des Luftverkehrs. Neben seinem Beitrag zum Treibhauseffekt steht hierbei die Lärmbelastung im Vordergrund.

We introduce a second quantization scheme based on quasinormal modes, which are the dissipative modes of leaky optical cavities and plasmonic resonators with complex eigenfrequencies. The theory enables the construction of multi-plasmon/photon Fock states for arbitrary three-dimensional dissipative resonators and gives a solid understanding to the limits of phenomenological dissipative Jaynes-Cummings models. In the general case, we show how different quasinormal modes interfere through an off-diagonal mode coupling and demonstrate how these results affect cavity-modified spontaneous emission. To illustrate the practical application of the theory, we show examples using a gold nanorod dimer and a hybrid dielectric-metal cavity structure., Comment: 6 pages, 3 figures

Mollow physics in the two-photon regime shows interesting features such as path-controlled time-reordering of photon pairs without the need to delay them. Here, we calculate analytically the two-photon correlations $ g^{(2)}(\tau)$, essential to discuss and study such phenomena in the resonant-driven dressed-state regime. It is shown that there exists upper and lower bounds of the $ g^{(2)}(\tau)-$ function for certain spectrally-selected photon pairs. Recent reported experiments agree with the presented theory and thereby it is shown that the resonant-driven four-level system is an interesting source for steerable quantum light in quantum cascade setups. We furthermore discuss the unlikeliness to observe antibunching for the delay time $ \tau=0 $ in the exciton-biexciton correlation functions in such experiments, since antibunching stems from a coherent and in-phase superposition of different photon emission events. Due to the occuring laser photon scattering, this coherent superposition state is easily disturbed and leads to correlation functions of $ g^{(2)}(0)=1$., Comment: 5 figures

Excitons dominate the optical properties of monolayer transition metal dichalcogenides (TMDs). Besides optically accessible bright exciton states, TMDs exhibit also a multitude of optically forbidden dark excitons. Here, we show that efficient exciton-phonon scattering couples bright and dark states and gives rise to an asymmetric excitonic line shape. The observed asymmetry can be traced back to phonon-induced sidebands that are accompanied by a polaron redshift. We present a joint theory-experiment study investigating the microscopic origin of these sidebands in different TMD materials taking into account intra- and intervalley scattering channels opened by optical and acoustic phonons. The gained insights contribute to a better understanding of the optical fingerprint of these technologically promising nanomaterials.

The rapidly increasing use of sensors throughout different research disciplines and the demand for more efficient devices with less power consumption depends critically on the emergence of new sensor materials and novel sensor concepts. Atomically thin transition metal dichalcogenides have a huge potential for sensor development within a wide range of applications. Their optimal surface-to-volume ratio combined with strong light-matter interaction results in a high sensitivity to changes in their surrounding. Here, we present a novel, highly efficient sensing mechanism to detect molecules based on dark excitons in these materials. We show that the presence of molecules with a dipole moment transforms dark states into bright excitons resulting in an additional pronounced peak in easy accessible optical spectra. This effect exhibits a huge potential for sensor applications, since it offers an unambiguous optical finger print for the detection of molecules - in contrast to common sensing schemes relying on small peak shifts and intensity changes., Comment: 6 pages, 4 figures

We investigate the polarization dependence of the carrier excitation and relaxation in epitaxial multilayer graphene. Degenerate pump-probe experiments with a temporal resolution of 30 fs are performed for different rotation angles of the pump-pulse polarization with respect to the polarization of the probe pulse. A pronounced dependence of the pump-induced transmission on this angle is found. It reflects a strong anisotropy of the pump-induced occupation of photogenerated carriers in momentum space even though the band structure is isotropic. Within 150 fs after excitation an isotropic carrier distribution is established. Our observations imply the predominant role of collinear scattering preserving the initially optically generated anisotropy in the carrier distribution. The experiments are well described by microscopic time-, momentum, and angle-resolved modelling, which allows us to unambiguously identify non-collinear carrier-phonon scattering to be the main relaxation mechanism giving rise to an isotropic distribution in the first hundred fs after optical excitation., Comment: Submitted to Nano Letters

We investigate a semiconductor quantum dot as a microscopic analog of a basic optomechanical setup. We show, that optomechanical features can be reproduced by the solid-state platform, arising from parallels of the underlying interaction processes, which in the optomechanical case is the radiation pressure coupling and in the semiconductor case the electron-phonon coupling. In optomechanics, phonons are typically induced via confined photons, acting on a movable mirror, while in the semiconductor system the phonons are emitted by the laser-driven electronic system. There are analogous effects present for both systems, featuring bistabilities, optically induced phonon lasing and enhanced phonon loss. Nonetheless, the different statistical nature of the optical cavity and the electronic system also leads to qualitative differences., Comment: 27 pages, 8 figures

We study the carrier dynamics in epitaxially grown graphene in the range of photon energies from 10 - 250 meV. The experiments complemented by microscopic modeling reveal that the carrier relaxation is significantly slowed down as the photon energy is tuned to values below the optical phonon frequency, however, owing to the presence of hot carriers, optical phonon emission is still the predominant relaxation process. For photon energies about twice the value of the Fermi energy, a transition from pump-induced transmission to pump-induced absorption occurs due to the interplay of interband and intraband processes.

We investigate the effect of the Coulomb interaction on the applicability of quantum gates on a system of two Coulomb-coupled quantum dots. We calculate the fidelity for a single- and a two-qubit gate and the creation of Bell states in the system. The influence of radiative damping is also studied. We find that the application of quantum gates based on the Coulomb interaction leads to significant input state-dependent errors which strongly depend on the Coulomb coupling strength. By optimizing the Coulomb matrix elements via the material and the external field parameters, error rates in the range of $10^{-3}$ can be reached. Radiative dephasing is a more serious problem and typically leads to larger errors on the order of $10^{-2}$ for the considered gates. In the specific case of the generation of a maximally entangled Bell state, error rates in the range of $10^{-3}$ can be achieved even in the presence of radiative dephasing., Comment: 8 pages, 10 figures; final version

We present a theory for the intersubband absorption including electronic ground state correlations in a doped GaAs/Al_{35}Ga_{65}As quantum well system. Focusing on the influence of the Coulomb interaction among the carriers at low temperatures, we find that the ground state correlations lead to an increased renormalization and spectral broadening of the absorption spectrum. At T = 1 K, its full width at half maximum is increased by up to a factor 3. The inclusion of electron-phonon scattering strongly reduces the relative impact of the electronic correlations., Comment: 5 pages, 5 figures

During the past two decades, international trade in telecommunication services has significantly intensified. What is more, an increasing number of telecommunications operators have begun to expand their activities beyond national borders through FDIs, joint ventures, and cooperation agreements. In this paper it is argued, however, that in spite of the rather successful efforts of late to liberalize the telecommunications sector (networks and services) at the regional (EU) and the global (WTO) level, much remains to be done to create and preserve a truly open and competitive worldwide telecommunications market.

This thesis studies ultrafast relaxation processes in semiconducting single-walled carbon nanotubes (SWCNTs) related to the fundamental process of photoluminescence excitation (PLE) and pump-probe experiments. Using carbon nanotube Bloch equations within the density matrix formalism we resolve ultrafast relaxation dynamics in momentum and time. This microscopic view elucidates the pathway of optically generated non-equilibrium carriers via intra- and intersubband scattering with optical and acoustic phonons approach to equilibrium within the lowest lying conduction subbands. Our analytical solutions of the Boltzmann-like scattering equations have successfully explained the influence of the tube intrinsic intersubband gap and subband curvature. In addition, the derived tube and phonon-mode specific electron-phonon matrix elements emphasize the influence of the coupling strength. Our model demonstrates that intersubband scattering is only possible with a sufficiently large energy provided by an optical phonon mode. Furthermore, we show that these optical phonons dominate during the intra-subband relaxation within the first hundred femtoseconds, while acoustic phonons with their small continuous energy primarily govern the relaxation towards equilibrium. The derived dynamics enabled us to extract relaxation times that exhibited clearly different timescales: processes driven by optical phonons occur within a few hundred femtoseconds, while those driven by acoustic phonons acting towards the band edge take up to a few picoseconds. Compared to experimental pump-probe studies on semiconducting SWCNTs, we find that the calculated relaxation times in the picosecond range fit very well with the observed initial decay time from the measured multiexponential differential transmission curves. Using our theoretical model we ascribed the observed picosecond relaxation time to intraband scattering about the band edge with acoustic phonons. Our approach allows us to study a large number of nanotubes, predicting a strong diameter and a weak chirality dependence of the relaxation times. A recent pump-probe study tuning the excitation and probe energy resonant around the optical transitions E22 and E11 observed a slowing-down of probing towards E11 in excellent agreement with our model. We also studied the effects of field enhancements of nanostructured hybrid electrode surfaces that has been fruitfully utilized to analyze biological systems in surface-enhanced Raman (SE(R)R) spectroscopy studies. The complete Maxwell equations were solved using finite-element methods with a view toward topology optimization for field enhancement in experimentally investigated hybrid systems. With field distribution calculations we comprehensively describe the observed effects in SE(R)RS experiments for probe-molecules adsorbed to a multilayered (Ag − SiO2 − Pt) electrode. Our results have enabled experimentalists to understand the nature of defects in the Pt film, which generate localized surface plasmons (LSPs) and field hot spots rising the average SE(R)RS enhancement to approx. 80 %. Our model successfully predicted a recent experimental study on a semiconductive nanostructured titanium dioxide (TiO2) electrode. The observed rising enhancement factor dependence on the anodization voltage may be straightforwardly rationalized from our calculations revealing that the this trend originates from the increasing anisotropy in the surface morphology. In summary, this thesis contributes to the understanding of the fundamental PLE process and also unfold the relevant phonon scattering channels of the observed relaxation time behavior in two-color pump-probe studies by affording microscopically resolved relaxation dynamics in semiconducting single-walled carbon nanotubes. Additionally, our field enhancement calculations of nanostructured electrodes reveal the underlying mechanisms that shall enable the optimization of hybrid devices for surface chemistry and biological application., Die vorgelegte Dissertation beschäftigt sich mit ultraschnellen Relaxationsprozessen in halbleitenden einwandigen Kohlenstoffnanoröhrchen (SWCNTs) und trägt bei zum Verständnis des fundamentalen Prozesses der Photolumineszenz-Anregung sowie korrespondierenden Pump-Probe-Experimenten. Durch die Herleitung von Kohlenstoffnanoröhrchen-Bloch-Gleichungen, die auf dem Formalismus der Dichtematrix basieren, wird eine in Impuls und Zeit aufgelöste ultraschnelle Relaxationsdynamik erzeugt. Die mikroskopische Betrachtungsweise erlaubt es den Bewegungsverlauf von optisch angeregten Nichtgleichgewichts Ladungsträgern ins Gleichgewicht nachzuvollziehen. Dieser wird von Intra- und Intersubband-Streuprozessen mit optischen und akustischen Phononen innerhalb der energetisch niedrigsten beiden Leitungsbänder bestimmt. Die analytischen Lösungen der Boltzmann-ähnlichen Streugleichungen erlauben die Interpretation der Relaxationsdynamik, durch die jedem Nanoröhrchen eigene Bandlücke und Krümmung der Subbänder. Darüber hinaus wird mittels durch die spezifischen Nanoröhrchen und der Phononenmoden hergeleiteten Elektron-Phonon-Matrixelemente der Einfluss der Kopplungsstärke hervorgehoben. Unser Modell zeigt auf, dass Intersubband-Streuung nur mit einer ausreichend großen Energie möglich ist, wie sie von einer optischen Phononenmode zur Verfügung gestellt wird. Weiterhin wird gezeigt, dass jene optischen Phononen bei der Intersubband-Relaxation während der ersten hundert Femtosekunden dominieren, während akustische Phononen durch ihre kleine kontinuierliche Energie in erster Linie die Relaxation ins Gleichgewicht führen. Die numerisch simulierte Dynamik ermöglicht es, Relaxationszeiten zu extrahieren, die deutlich unterschiedliche Zeitskalen aufweisen: Durch optische Phononen getriebene Prozesse treten innerhalb weniger hundert Femtosekunden auf, während die durch akustische Phononen in Richtung Bandkante ablaufenden Relaxationszeiten bis zu einigen Pikosekunden reichen. Im Vergleich zu experimentellen Pump-Probe-Studien an halbleitenden SWCNTs stellt sich heraus, dass die berechneten Relaxationszeiten im Bereich von Pikosekunden sehr gut mit der beobachteten anfänglichen Abklingzeit der gemessenen multi-exponentiellen differentiellen Transmissionskurven übereinstimmen. Mit unserem theoretischen Modell können wir die beobachtete Pikosekunden-Relaxationszeit Intraband-Streuprozessen mit akustischen Phononen nahe der Bandkante zuordnen. Unser Ansatz ermöglicht es uns darüber hinaus, eine große Anzahl von Nanoröhrchen zu studieren, woraus sich die Vorhersage einer starken Durchmesser- und einer schwachen Chiralitätsabhängigkeit der Relaxationszeiten ergibt. In einer aktuellen Pump-Probe-Studie, in der die Pump- und Probe-Energie resonant um die optischen Übergänge E22 und E11 variiert wurde, konnte eine Verlangsamung der Relaxationszeiten bei der Ausrichtung der Probe-Energie zu E11 beobachtet werden, was hervorragend mit unserem Modell übereinstimmt. Desweiteren wurden die Auswirkungen von Feldverstärkungen an nanostrukturierten Oberflächen von Hybridelektroden untersucht, die erfolgreich eingesetzt werden können, um biologische Systeme in oberflächenverstärkten Raman-(SE(R)R)-Spektroskopie-Studien zu analysieren. Die vollständigen Maxwell-Gleichungen wurden hierbei unter Verwendung von Finite-Elemente-Methoden im Hinblick auf die Optimierung der Topologie zur Feldverstärkung in den experimentell untersuchten Hybridsystemen gelöst. Mit Berechnungen zur elektrischen Feldverteilung beschreiben wir ausführlich die beobachteten Effekte in SE(R)RS-Experimenten für Probenmoleküle, adsorbiert an einer mehrschichtigen (Ag − SiO2 − Pt) Elektrode. Unsere Ergebnisse ermöglichten es den Experimentatoren, den Einfluß der Fehlstellen in der Pt-Film-Oberfläche zu verstehen, die ihrerseits lokalisierte Oberflächenplasmonen (LSPs) und Field Hotspots erzeugten, wodurch die durchschnittliche SE(R)RS-Verstärkung 80 % erreichte. Das entwickelte Modell wurde daraufhin erfolgreich in einer fortführenden aktuellen experimentellen Studie an halbleitenden nanostrukturierten Titandioxid (TiO2) Elektroden erweitert. Die beobachtete ansteigende Verstärkung in Abhängigkeit von der Anodisierungsspannung kann direkt aus den Berechnungen abgeleitet werden, wobei sich herausstellt, dass dieser Trend der zunehmenden Anisotropie der Oberflächenmorphologie zu Grunde liegt.