Composite-Cavity Organic Microlasers

This thesis deals with the development and investigation of composite-cavity (CC) organic microresonators comprising a vertical cavity (VC) and a distributed feedback structure (DFB). Prepared as separate devices, these two resonators are extensively investigated and characterized by their far-field radiation patterns, emission spectra, and dispersion characteristics. Although the vertical and lateral systems are based on entirely different concepts leading to distinct symmetries, confinement mechanisms, and processes of optical feedback, devices produced with the same set of materials show comparable lasing thresholds. The different angular dispersions of cavity and waveguide (WG) resonances are employed in a laterally structured vertical-cavity surface-emitting laser (VCSEL), where a periodic grating serves as a diffractive coupler between these two regimes. A coherent interaction of the vertical and horizontal system is observed as pronounced anticrossings of parabolic and linear dispersion curves in the far-field spectra. As a result from this coherent coupling, the hybridized WG-VCSEL modes show stimulated emission in far-field regions, where the individual photonic structures would not reach the lasing threshold in a decoupled scenario. Efficient optical feedback in surface-normal and in-plane direction is achieved by combining a VC and a second-order DFB structure in a continuous tunable CC microresonator. The optical coupling is due to a first-order light diffraction on a second-order Bragg grating and, in the degenerate case, can be as efficient as the coupling observed in more classical cascade coupled cavities. When the system is non-degenerate, the diffraction efficiency is suppressed because of sub-coherence-length dimensions of the composite-cavity and both resonators tend to operate as independent structures, without experiencing substantial losses due to diffraction on the distributed-feedback grating. Dispersion characteristics of multiple resonances are recorded and related to calculated modes, their field profiles, and coupling efficiencies. In combination with the analysis of input-output measurements, the lasing characteristics of vertical and lateral resonances are controlled by adjusting specific design parameters of the system. For identical resonance energies, the distinct resonators show coherent interaction in the cross-coupled configuration, if the quality of the resonances and the cross-coupling efficiency meet the condition of strong photon-photon interaction. This resonant coupling has a fundamental impact on dispersion and lasing characteristics of the system.Die vorliegende Arbeit beschäftigt sich mit der Entwicklung und Untersuchung von organischen Mikroresonatoren, die eine Kompositkavität aus einem Oberflächenemitter und einem Resonator mit verteilter Rückkopplung (DFB) beinhalten. Diese beiden Resonatortypen werden zunächst als separate Strukturen hergestellt, untersucht und über deren Intensitätsverteilungen im Fernfeld, Emissionsspektren und Dispersionseigenschaften charakterisiert. Die vertikalen und lateralen Strukturen basieren auf unterschiedlichen Konzepten, die zu völlig verschiedenartigen Symmetrien, Mechanismen des elektromagnetischen Einschlusses und Arten der optischen Rückkopplung führen. Nichtsdestotrotz weisen diese Resonatoren, die mit dem gleichen Materialsatz hergestellt wurden, ähnliche Laserschwellen auf. Die unterschiedliche winkelabhängige Dispersion von Vertikal- und Wellenleitermoden werden in einem lateral strukturierten Oberflächenemitter (VCSEL) ausgenutzt. In dieser Struktur dient eine periodisches Gitter als Kopplungselement zwischen diesen beiden Bereichen. Eine kohärente Wechselwirkung zwischen vertikalem und horizontalem System zeigt sich durch das Auftreten von ausgeprägten Antikreuzungspunkten parabolischer und gerader Dispersionskurven in den winkelaufgelösten Emissionsspektren. Die Folge dieser kohärenten Kopplung ist das Entstehen von Lasermoden in Bereichen des Fernfelds, wo die einzelnen Resonatoren im entkoppelten Zustand die Laserschwelle nicht erreichen würden. Eine wirksame optische Rückkopplung sowohl in Richtung der Oberflächennormalen als auch in lateraler Richtung wird durch die Kombination einer VCSEL und einer DFB-Struktur zweiter Ordnung in einem kontinuierlich durchstimmbaren Kompositresonator erreicht. Die optische Kopplung wird durch Beugung erster Ordnung am Bragg-Gitter zweiter Ordnung realisiert. Im entarteten Fall werden Kopplungseffizienzen beobachtet, die vergleichbar mit denen klassisch kaskadengekoppelter Mikrokavitäten sind. Für verschiedene Energieeigenwerte der zwei Resonatorkomponenten führt die im Vergleich zur Kohärenzlänge geringe Ausdehnung der Kompositkavität zu einer nahezu unabhängigen Tätigkeit der beiden Resonatoren mit nur geringen Verlusten durch Beugung an der periodischen Struktur. Die Dispersionseigenschaften von mehreren Resonanzen werden gemessen und berechneten Moden, deren Feldverteilungen und Kopplungseffizienzen zugeordnet. In Verbindung mit der Analyse der Intensitäten der Lasermoden in Abhängigkeit der Pumpleistung werden die Laserschwellen durch die Anpassung spezifischer Designparameter kontrolliert. Für identische Resonanzenergien weisen die unterschiedlichen Resonatoren eine kohärente Wechselwirkung auf, falls die Qualität der Moden und die Beugungseffizienz die Bedingung für starke Photon-Photon-Kopplung erfüllen. Diese resonante Kopplung zeigt einen fundamentalen Einfluss auf die Dispersions- und Lasereigenschaften im Kompositsystem

Integer Partitions Under Certain Finiteness Conditions

This dissertation focuses on problems related to integer partitions under various finiteness restrictions. Much of our work involves the collection of partitions fitting inside a fixed partition $\lambda$, and the associated generating function $G_{\lambda}$. In Chapter 2, we discuss the flawlessness of such generating functions, as proved by Pouzet using the Multicolor Theorem. We give novel applications of the Multicolor Theorem to re-prove flawlessness of pure $O$-sequences, and show original flawlessness results for other combinatorial sequences. We also present a linear-algebraic generalization of the Multicolor Theorem that may have far-reaching applications. In Chapter 3, we extend a technique due to Stanton to prove unimodality of $G_\lambda$ for certain infinite families of partitions $\lambda$ in 5 and 6 parts. Our most substantial work is presented in Chapter 4, where we initiate the study of the novel poset \ds{P_n=\{G_\lambda\,|\,\lambda\vdash n\}}. We describe some general structural properties of this poset. Of greatest significance is our result that two ``balancing operations on the principal hooks of a partition $\lambda$ produce generating functions at least as large as $G_{\lambda}$ (in the ordering of $P_n$), hereby imposing a strong necessary condition on the maxima of $P_n$. We conjecture an asymptotic value of $|P_n|$, and show that determining $|P_n|$ exactly appears to be nontrivial. This we demonstrate by providing an infinite family of non-conjugate pairs of partitions that have the same generating function. Finally, we prove asymptotic results on the number of maxima in this poset

The Impact of IT on Competitive Advantage

How can an organization establish an efficient IS resource? Over the years, the resource-based view (RBV) has provided important insights into the value creation by IT. Unfortunately, large parts of the literature suffer from broad and ambiguous constructs that are problematic to validate and difficult to concretely apply. Furthermore, the transmission from IT resources on one side to competitive advantage on the other is not yet sufficiently understood. Goal of this paper is to clarify some of the often used constructs and build a framework for the transmission from the endowment with resources to the achievement of competitive advantage. In this paper, we aim to contribute to this research strand in two ways. First, a model incorporating many isolated findings from the RBV is developed. Reflecting the need for a process view as proposed by large parts of the alignment and strategic management literature, this is integrated into a single process framework of analysis. Second, by augmenting a microeconomic production function incorporating organizational routines the transmission from IT resource to better business process performance is explicated, allowing simultaneous parameter sensitivity analysis and contributing to making the RBV applicable and open for empirical research

The Role of Alignment for Strategic Information Systems: Extending the Resource Based Perspective of IT

The importance of strategic information systems (SIS) in the financial industry is documented in many studies. But still there is a virulent lack of frameworks to explain the profit impact of IT in general and to guide firms in exploiting the IT resource as a source of competitive advantage. By incorporating findings from the resource based view (RBV) and strategic alignment literature we elaborate key concepts potentially leading to a sustained competitive advantage (SCA). Supported by four case studies from the financial services industry, our findings suggest that the exploitation of SIS for achieving SCA requires IT business alignment based on organizational routines of cross-departmental interaction. These concepts are explicitly modeled and integrated into a formal model using microeconomic theory. Especially interactions between the IT and business domain are found to be a key success driver

Warped Fermions and Precision Tests

We analyze the behavior of Standard Model matter propagating in a slice of AdS_5 in the presence of infrared-brane kinetic terms. Brane kinetic terms are naturally generated through radiative corrections and can also be present at tree level. The effect of the brane kinetic terms is to expell the heavy KK modes from the infrared-brane, and hence to reduce their coupling to the localized Higgs field. In a previous work we showed that sizable gauge kinetic terms can allow KK mode masses as low as a few TeV, compatible with present precision measurements. We study here the effect of fermion brane kinetic terms and show that they ameliorate the behavior of the theory for third generation fermions localized away from the infrared brane, reduce the contribution of the third generation quarks to the oblique correction parameters and mantain a good fit to the precision electroweak data for values of the KK masses of the order of the weak scale.Comment: 25 pages, 4 figures, latex2