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Now showing items 41-50 of 330
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 ...
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
Raumwinkeloptimierte Elektron-Photon Koinzidenzmessungen nach der Anregung mit Synchrotronstrahlung unter Verwendung zeitlich verschieden strukturierter Füllmuster des Speicherrings
(2021-05)
Für die Untersuchung von Relaxationspfaden von angeregten mikroskopischen Systemen nehmen Messmethoden eine zentrale Rolle ein, bei denen emittierte Teilchen so gemessen werden, dass eine physikalische Korrelation zwischen Ihnen nachgewiesen werden kann. Denn nur durch den Nachweis dieser Korrelationen ist es bei stark verzweigten und sich unter Umständen kreuzenden Relaxationspfaden, diese Pfade eindeutig nachzuverfolgen.
Diese sogenannten Koinzidenzmessungen werden seit ihren ersten Anwendungen in den 1920er Jahren ...
Aufsatz
Electronic origin of bond softening and hardening in femtosecond-laser-excited magnesium
(IOP, 2014)
Many ultrafast structural phenomena in solids at high fluences are related to the hardening or softening of particular lattice vibrations at lower fluences. In this paper we relate femtosecond-laser-induced phonon frequency changes to changes in the electronic density of states, which need to be evaluated only in the electronic ground state, following phonon displacement patterns. We illustrate this relationship for a particular lattice vibration of magnesium, for which we—surprisingly—find that there is both softening ...
Aufsatz
Controlling the transport of an ion: classical and quantum mechanical solutions
(IOP, 2014)
The accurate transport of an ion over macroscopic distances represents a challenging control problem due to the different length and time scales that enter and the experimental limitations on the controls that need to be accounted for. Here, we investigate the performance of different control techniques for ion transport in state-of-the-art segmented miniaturized ion traps. We employ numerical optimization of classical trajectories and quantum wavepacket propagation as well as analytical solutions derived from invariant ...