Mikroskopische Analyse optoelektronischer Eigenschaften von Halbleiterverstärkungsmedien für Laseranwendungen

Eine mikroskopische Vielteilchentheorie wird auf verschiedenste Materialsysteme angewendet, die als Verstärkungselement den Grundbaustein von Halbleiterlasersystemen bilden. Das Verständnis der mikroskopischen Prozesse und ihre Modellierung ermöglichen die Analyse und quantitative Prognose optoelektronischer Eigenschaften, die das Laserverhalten maßgeblich bestimmen. Mit dem Modell lassen sich Materialeigenschaften treffend simulieren, wie umfassende Theorie-Experiment-Vergleiche zeigen. Die Untersuchung von Absorption, optischer Verstärkung, Lumineszenz und intrinsischen Ladungsträgerverlusten durch strahlende sowie Auger-Rekombination bildet den Leitfaden zur Charakterisierung verschiedenster Halbleiterverstärkungsmedien. Darauf aufbauend werden nicht nur Lasereigenschaften wie Emissionswellenlängen und Schwellenverhalten berechenbar, sondern es lassen sich auch unbekannte und experimentell schwer zugängliche Strukturparameter bestimmen. So können Konzepte erarbeitet werden, mit denen Laserdesigns mit Blick auf die Anforderungen spezifischer Anwendungen hin optimiert und weiterentwickelt werden können, und mit denen neuartige Lasersysteme auf ihr Anwendungspotential hin eingeschätzt und bewertet werden können

Nambu-Jona-Lasinio Models Beyond the Mean Field Approximation

Inspired by the model of Nambu and Jona-Lasinio, various Lagrangians are considered for a system of interacting quarks. Employing standard techniques of many-body theory, the scalar part of the quark self-energy is calculated including terms up to second-order in the interaction. Results obtained for the single-particle Green's function are compared with those which only account for the mean-field or Hartree-Fock term in the self-energy. Depending on the explicit form of the Lagrangian, the second-order contributions range between 4 and 90 percent of the leading Hartree-Fock term. This leads to a considerable momentum dependence of the self-energy and the effective mass of the quarks.Comment: 17 page

Two-color STED microscopy reveals different degrees of colocalization between hexokinase-I and the three human VDAC isoforms

The voltage-dependent anion channel (VDAC, also known as mitochondrial porin) is the major transport channel mediating the transport of metabolites, including ATP, across the mitochondrial outer membrane. Biochemical data demonstrate the binding of the cytosolic protein hexokinase-I to VDAC, facilitating the direct access of hexokinase-I to the transported ATP. In human cells, three hVDAC isoforms have been identified. However, little is known on the distribution of these isoforms within the outer membrane of mitochondria and to what extent they colocalize with hexokinase-I. In this study we show that whereas hVDAC1 and hVDAC2 are localized predominantly within the same distinct domains in the outer membrane, hVDAC3 is mostly uniformly distributed over the surface of the mitochondrion. We used two-color stimulated emission depletion (STED) microscopy enabling a lateral resolution of ~40 nm to determine the detailed sub-mitochondrial distribution of the three hVDAC isoforms and hexokinase-I. Individual hVDAC and hexokinase-I clusters could thus be resolved which were concealed in the confocal images. Quantitative colocalization analysis of two-color STED images demonstrates that within the attained resolution, hexokinase-I and hVDAC3 exhibit a higher degree of colocalization than hexokinase-I with either hVDAC1 or hVDAC2. Furthermore, a substantial fraction of the mitochondria-bound hexokinase-I pool does not colocalize with any of the three hVDAC isoforms, suggesting a more complex interplay of these proteins than previously anticipated. This study demonstrates that two-color STED microscopy in conjunction with quantitative colocalization analysis is a powerful tool to study the complex distribution of membrane proteins in organelles such as mitochondria

Quantum modeling of semiconductor gain materials and vertical-external-cavity surface-emitting laser systems

This article gives an,overview of the microscopic theory,theory used to quantitatively model a wide range of semiconductor laser gain materials. As a snapshot of the current state of research, applications to a variety of actual quantum-well systems are presented. Detailed theory experiment comparisons are shown and it is analyze how the theory can be used to extract poorly known material parameters. The intrinsic laser loss processes due to radiative and nonradiative Auger recombination are evaluated microscopically. The results are used for realistic simulations of vertical-external-cavity surface-emitting laser systems. To account for nonequilibrium effects, a simplified model is presented using pre-computed microscopic scattering and dephasing rates. Prominent deviations from quasi-equilibrium carrier distributions are obtained under strong in-well pumping conditions

Two-color STED microscopy in living cells

Diffraction-unlimited resolution provided by Stimulated Emission Depletion (STED) microscopy allows for imaging cellular processes in living cells that are not visible by conventional microscopy. However, it has so far not been possible to study dynamic nanoscale interactions because multicolor live cell STED microscopy has yet to be demonstrated and suitable labeling technologies and protocols are lacking. Here we report the first realization of two-color STED imaging in living cells. Using improved SNAPf and CLIPf technologies to label epidermal growth factor (EGF) and EGF receptor (EGFR), we report resolutions of 78 nm and 82 nm for 22 sequential two-color scans in living cells

Formation of a Bazooka–Stardust complex is essential for plasma membrane polarity in epithelia

Recruitment of the Crumbs–Stardust polarity complex depends on interactions between Bazooka and the Stardust PDZ domain and is regulated by aPKC-mediated phosphorylation

Microscopic electroabsorption line shape analysis for Ga(AsSb)∕GaAs heterostructures

A series of Ga(AsSb)/GaAs/(AlGa) As samples with varying GaAs spacer width are studied by electric-field modulated absorption (EA) and reflectance spectroscopy and modeled using a microscopic theory. The analysis of the Franz-Keldysh oscillations of GaAs capping layer and of the quantum-confined Stark shift of the lowest quantum well (QW) transitions shows the strong inhomogeneity of the built-in electric field indicating that the field modulation due to an external bias voltage differs significantly for the various regions of the structures. The calculations demonstrate that the line shape of the EA spectra of these samples is extremely sensitive to the value of the small conduction band offset between GaAs and Ga(AsSb) as well as to the magnitude of the internal electric field changes caused by the external voltage modulation in the QW region. The EA spectra of the entire series of samples are modeled by the microscopic theory. The good agreement between experiment and theory allows us to extract the strength of the modulation of the built-in electric field in the QW region and to show that the band alignment between GaAs and Ga(AsSb) is of type II with a conduction band offset of approximately 40 meV.</p