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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
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
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
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 ...
Dissertation
InP - based quantum dots for telecom wavelengths ranges
(2019-12)
Long-distance quantum communication applications require sources of single photons, emitting at telecom wavelengths (around 1550 nm) with minimum attenu-ation losses of silica fiber.
Semiconductor self-assembled InAs/InP-based quantum dots (QDs) are possible candidates to
reach this spectral region. One of the challenges on the way is a QD asymmetry, which limits the fidelity of entangled photons. Therefore, morphological and optical properties of QDs should be improved in order to achieve the necessary quality and ...
Dissertation
Abhängigkeit des Exchange-Bias Feldes und des Koerzitivfeldes von der mittels Röntgendiffraktometrie gemessenen Kornvolumenverteilung des Antiferromagneten in Exchange-Bias Schichtsystemen
(2019-10-02)
Der Exchange-Bias Effekt wird in vielen technischen Anwendungen, wie z.B. in magnetischen Speichermedien oder in Magnetsensorköpfen zum Pinnen der Magnetisierungsrichtung der Referenzelektrode, eingesetzt. Dieser Effekt tritt ausschließlich in dünnen Schichtsystemen, in denen sich ein dünner Ferromagnet mit einem dünnen Antiferromagneten in Kontakt befindet, auf und bewirkt eine Verschiebung der Hysteresekurve entlang der Magnetfeldachse. Solche Exchange-Bias Schichtsysteme können mittels Ionenbeschuss, d.h., leichte ...
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
Molecular-Frame Angular Distributions of Electrons Emitted by Photoionization and Interatomic Coulombic Decay
(2020)
The continuous refinement of the experimental and theoretical methods to study the electron angular emission distributions, and particularly in a molecule frame of reference, have contributed to a keen understanding of the structure of molecules and have provided deeper insight into fundamental physical phenomena.
Revealing many details of the ionization dynamics, the molecular-frame angular distributions (MFADs) of emitted electrons have been an appealing research topic for the last two decades. Owing to the ...