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Dissertation
Gold Surface Nanostructuring with Ultrashort Laser Pulses - Study of Non-equilibrium Effects
(2019)
Laser material interaction and structure formation in metals under controlled ultrashort laser pulse conditions are discussed in this work. A novel approach is presented describing the exact amount of energy deposited by a laser pulse in a gold surface, applicable under a variety of structuring conditions. The presented model is validated by a new introduced broad-band pump-probe reflectivity measurement method. A technique also applicable to investigate other phenomenas where 20 fs resolution combined with an octave ...
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
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 ...
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 ...
Aufsatz
Preferential weakening of rotational magnetic anisotropy by keV-He ion bombardment in polycrystalline exchange bias layer systems
(2018-05-04)
The consequences of keV light-ion bombardment of polycrystalline exchange bias layer systems on individual magnetic anisotropies composing the effective unidirectional magnetic anisotropy are investigated by vectorial magneto-optic Kerr effect measurements. Preferential reduction of rotatable magnetic anisotropy as compared to the other magnetic anisotropies is observable, disproving the intuitive assumption of an equable weakening of all magnetic anisotropies due to the bombardment. It is concluded that light-ion ...
Dissertation
Investigation of diamond nanostructures with incorporated color centers
(2018)
Diamond is a material with excellent properties due to its structure and composition. Its crystal lattice is a perfect host of different defect centers, so-called color centers, whose properties, especially the capability of emitting single photons, can serve in quantum information technologies (QIT). As a high refractive index material only a small part of the photons emitted by these color centers in diamond can be collected. To enhance the photon collection efficiency photonic structures are necessary. They can ...
Dissertation
Energy transfer in free-standing van der Waals heterostructures after optical excitation
(2019)
The wide range of layered van der Waals materials is interesting due to its plenty of deviating characteristics. The structure of all these materials is built from covalently joined layers, which are stacked by van der Waals forces. Aside from this structural similarity the specific characteristics spread out in a variety of electronic and optical properties. The electronic properties of layered materials vary from pure insulators to metallic conductors and can even depend on the number of layers. In the work presented ...
Dissertation
Ab-initio analysis of the structural response of solids after femtosecond-laser-pulse excitation
(2019)
After an intense femtosecond-laser excitation extreme non-equilibrium conditions are induced in materials. The high photon density in such an ultrashort-laser pulse interacts directly with the electronic system of the material. By absorbing the photon energy the electrons are excited in high energy states, where they form a non-equilibrium distribution shortly after the excitation. Due to fast electron-electron scattering and cascading processes equilibrates the electronic system within several femtoseconds to a ...
Aufsatz
Exploiting non-Markovianity for quantum control
(Nature Publishing Group, 2015)
Quantum technology, exploiting entanglement and the wave nature of matter, relies on the ability to accurately control quantum systems. Quantum control is often compromised by the interaction of the system with its environment since this causes loss of amplitude and phase. However, when the dynamics of the open quantum system is non-Markovian, amplitude and phase flow not only from the system into the environment but also back. Interaction with the environment is then not necessarily detrimental. We show that the ...