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Now showing items 21-30 of 121
Dissertation
High-Speed 1.55 µm Quantum Dot Lasers with Electronically Coupled Quantum Well - Dot Active Regions
(2019-07-31)
The expansion of long-distance data communication at a wavelength of 1.55 µm calls for larger data transfer rates. Consequently, an improvement of emission and modulation properties of lasers emitting in this wavelength region is of high interest. The utilization of so-called tunnel-injection (TI) structures in InP-based quantum dot (QD) lasers is promising to fulfill this task. The aim of this thesis was the realization and analysis of TI structures in the lattice matched InP material system and incorporation into ...
Dissertation
Analysis of near-substrate magnetic particle transport for Lab-on-a-chip applications: stray field modulations, influence of particle properties and three-dimensional trajectories
(2022)
Die Entwicklung schneller und zuverlässiger Diagnostik ist ein wichtiges Ziel für die Früherkennung von Krankheiten. Standardisierte Labormethoden sind heutzutage meist langsam und mit hohen Kosten verbunden. Innerhalb der Lab-on-a-chip (LOC)-Technologie kann der Nachweis eines pathogenen Organismus auf die Größe eines kleinen Chips miniaturisiert werden, indem magnetische Partikel als Fängerobjekte integriert werden. Die Kombination einer statischen Magnetfeldlandschaft (MFL) mit zeitlich variierenden externen ...
Dissertation
Magnetic Textures and Magnetization Reversal Processes in Arrays of Ferromagnetic and Exchange-Biased Hollow Hemispheres
(2022)
The main objective of this thesis is to investigate hemispherical caps prepared by thin film deposition of magnetic material compositions on top of nano- and micrometer sized silica spheres. When compared to flat magnetic discs, these microcaps differ in their magnetic properties due to the curved and therefore three-dimensional shape. However, under certain conditions, both microstructures have previously been proven to express the famous magnetic vortex texture because of the confinement into a circular shape. ...
Dissertation
Electronic Theory of the Magnetic Order, Anisotropy and Reversal Processes in Rolled-Up Stripes and Thin Films
(2022)
A comprehensive multiscale approach consisting of a combination of state of the art, first principles quantum theory and the flexible statistical methodologies of complex systems is applied in order to achieve a detailed microscopic understanding of the magnetic properties of rolled-up transition-metal [TM] ultrathin films and stripes. A quantum electronic investigations of the effective interactions between the local magnetic moments is performed as a function of composition and rolling radius R including the limit ...
Dissertation
Investigations on Diamond Thin Films as Implant Coating and Biosensing Platform
(2021)
Diamond is researched in biological context for decades. Fundamental research has established diamond as a material that combines a pronounced compatibility with biological entities and resilience against even the harshest chemical and physical conditions. The present dissertation strives to improve the abilities of diamond in this matter even further by utilizing methods of nanostructuring and biochemical functionalization. Numerous characterization methods are used to monitor each step in detail and to evaluate the ...
Dissertation
1.55 μm Quantum Dot Lasers for Telecommunication
(2019)
The thesis at hand investigates the suitability of quantum dot (QD) material for use in long-distance coherent communication. The thesis was written in the frame of the SASER project MONOLOP that is aiming for a compact, monolithically integrated light source with a tunable wavelength covering the C+-band and narrow spectral linewidth below 500 kHz.
The thesis reviews the theoretical background of quantum dot material based on the InP material system and distributed feedback (DFB) lasers with lateral gratings as ...
Dissertation
Optimal Control of Quantum Information Tasks in Open Quantum Systems
(2020-07-30)
Every quantum system inevitably interacts with its environment. This is a fundamental requirement that allows us to control, measure and, in general, interact with quantum systems. In that respect, a quantum system's openness can be interpreted as prerequisite that enables quantum technologies in the first place. The latter are built to harness the intrinsic quantum mechanical behavior of quantum devices in order to build new, powerful technologies. However, a quantum system's openness also causes it to interact ...
Dissertation
Development of Carrier-Envelope-Phase-Stabilized, mJ-Class Laser Sources Generating Intense, Few-Cycle Laser Pulses
(2020-05-19)
Over a decade ago the frontiers of ultrashort physics and nonlinear optics have reached the attosecond timescale ($1 as = 10 ^ {-18} s$) . Currently, in order to generate isolated attosecond pulses, an intense femtosecond pulse is focused in a jet of a noble gas. Given the sufficient intensity, this leads to high harmonic generation (HHG), which can be filtered (gated) to create a single isolated attosecond pulse. The laser source for the driver pulses has to fulfill two requirements: the pulses need to be limited ...
Dissertation
Bestimmung der mittleren Clustergröße und ortsspezifischen Zustände homogener Edelgascluster mittels Fluoreszenzspektroskopie
(2021)
Der Übergang von mikroskopischen zu makroskopischen Systemen ist in den Naturwissenschaften von grundlegendem Interesse, da im zugehörigen Übergangsbereich größenabhängige Entwicklungen physikalischer Eigenschaften sowie auch gänzlich neue Prozesse auftreten. Edelgascluster ermöglichen einen experimentellen Zugang zur Untersuchung dieses Zwischenbereichs.
Die durch Van-der-Waals-Kräfte gebundenen inerten Edelgasatome fungieren als Prototypsysteme zur Untersuchung derartiger fundamentaler Prozesse. Sie werden mittels ...
Dissertation
Quantum optimal control theory of photoelectron spectroscopy
(2018)
The object of this doctoral thesis is two-fold and can be classified into two, but intrinsically related categories: (i) development of theoretical models for the simulation of electron dynamics and in parallel to this, (ii) method development of efficient numerical algorithms for ad hoc control of photoelectron and photoion-related observables. The first category primarily focuses on the development of a variety of theoretical models describing the interaction of light and matter for the extraction and control of ...