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The Global ETD Search service is a free service for researchers
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Showing 1 to 10 of 13 (0.008 seconds)| 1 |
Models in nonlinear condensed-matter optics: From theory to experimentVoit, Kay-Michael 12 April 2013 (has links)
Cumulative Dissertation on models in nonlinear condensed-matter
optics. In chapter 2, the coupled-wave theory first introduced by Kogelnik is reviewed
and extended with emphasis on out-of-phase mixed holographic gratings. This class of
gratings becomes increasingly important due to novel methods of hologram recording
and new classes of materials and metamaterials like holographic polymer dispersed
liquid crystals. Additionally, advances in laser technology suggest a stronger spectro-
scopic view on holography. The model presented in this thesis accounts for both of
these demands and provides a closed analytical solution.
Chapter 3 contributes to the field of space-charge waves (SCW), which provides
powerful tools for material analysis, especially in semiconductor technology. Although
the underlying theory is generally understood, recent improvements of the ex-
perimental techniques required extensions of the model and the interpretation of new
effects. In this thesis, the existing formalism is adapted to a new method of excitation,
which not only simplifies the experimental setup, allowing for easier adoption into
industrial environments, but also provides insight into the direction of carrier motion.
Furthermore, the model is extended to describe the influence of an external magnetic
field, adding the possibility to examine the Hall mobility of carriers.
Eventually, chapter 4 studies the dynamics of light induced absorption in pho-
tochromic [Ru(bpy)2 (OSO)]+ . Compared to other photofunctional compounds, this
molecule is nontoxic and exhibits exceptional photochromic reactions. These properties
make it a promising candidate for important industrial and technological applications,
ranging from data storage to non-electronic computation. For a profound analysis,
the models used for the description of photofunctional molecules have been
completely revised to account for the pronounced absortion changes in the material.
Furthermore, a setup with orthogonal pump and probe beams is modeled and exper-
imentally tested. This novel geometry is introduced to resemble common industrial
setups.
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Arrival times in quantum mechanics: Operational and quantum optical approaches / Ankunftszeiten in der Quantenmechanik: Operative und quantenoptische AnsätzeSeidel, Dirk 06 July 2005 (has links)
No description available.
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Raumzeitliche Dynamik optisch angeregter Elektron-Loch-Plasmen in Galliumarsenid / Spatio-temporal kinetics of optically generated electron-hole plasmas in GaAsZiebold, Ralf 25 October 2000 (has links)
No description available.
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Numerische Untersuchungen zum optischen Durchbruch von Femtosekunden-Laserpulsen in Wasser / Numerical investigations of the optical breakdown of femtosecond laser pulses in waterKöhler, Karsten 13 October 2010 (has links)
No description available.
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Effects of Atom-Laser Interaction on Ultra-Cold Atoms / Effekte der Atom-Laser Wechselwirkung auf ultrakalte AtomeHannstein, Volker Martin 03 April 2006 (has links)
No description available.
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Untersuchungen zur laserinduzierten Kavitation mit Nanosekunden- und Femtosekundenlasern / Investigations of laser-induced cavitation using nanosecond and femtosecond lasersGeisler, Reinhard 31 October 2003 (has links)
No description available.
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The significance of coherent flow structures for the turbulent mixing in wall-bounded flows / Die Bedeutung kohärenter Strukturen für die turbulente Vermischung in WandgrenzschichtenKähler, Christian Joachim 01 July 2004 (has links)
No description available.
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Magnetization dynamics in all-optical pump-probe experiments: spin-wave modes and spin-current damping / Magnetisierungsdynamik in Pump-Probe Experimenten: Spinwellen Moden und Spinstrom DämpfungDjordjević Kaufmann, Marija 06 November 2006 (has links)
No description available.
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Recombination dynamics of optically generated small polarons and self-trapped excitons in lithium niobateMesserschmidt, Simon 02 July 2019 (has links)
Quasi-particles formed in lithium niobate after pulse exposure were investigated by transient absorption and photoluminescence spectroscopy as well as numerical simulations. This includes the formation process, the transport through the crystal, interim pinning on defects during the relaxation process, and the final recombination with deep centers. It was shown that the charge-transport through the crystal can be described by a hopping transport including different types of hops between regular or defective lattice sites, i.e., the transport includes a mixture of free and bound small polarons. Furthermore, the different types of hops connected with varying activation energies and their distribution are responsible for an altered temporal decay curve when changing the crystal composition or temperature.
Additionally, it was shown that the hitherto accepted recombination model is insufficient to describe all transient absorption and luminescence effects in lithium niobate under certain experimental conditions, i.e., long-living absorption dynamics in the blue/UV spectral range do not follow the typical polaron dynamics and cannot be described under the assumption of charge compensation. However, similar decay characteristics between self-trapped excitons known from photoluminescence spectroscopy and the unexpected behavior of the transient absorption were found leading to a revised model. This includes, besides the known polaron relaxation and recombination branch, a significant role of self-trapped excitons and their pinning on defects (pinned STEs).
Since the consideration of further absorption centers in the relaxation path after pulse exposure might result in misinterpretations of previously determined polaron absorption cross-sections and shapes, the necessity to perform a review became apparent. Therefore, a supercontinuum pump-probe experiment was designed and all measurements applied under the same experimental conditions (temperature, polarization) so that one can extract the absorption amplitudes of the single quasi-particles in a spectral range of 0.7-3.0eV. The detailed knowledge might be used to deconvolve the absorption spectra and transform them to number densities of the involved centers which enables one to obtain an easier insight into recombination and decay dynamics of small polarons and self-trapped excitons.
As the hopping transport of quasi-particles and the concept of pinned STEs might be fundamental processes, a thorough understanding opens up the possibility of their exploitation in various materials. In particular, results presented herein are not only limited to lithium niobate and its applications; an extension to a wide range of further strongly polar crystals in both their microscopic processes and their use in industry can be considered.
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Mutual interactions of femtosecond pulses and transient gratings in nonlinear optical spectroscopyNolte, Stefan 16 November 2018 (has links)
This work is dedicated to a comprehensive experimental study on the interaction of femtosecond laser pulses with the nonlinear optical medium lithium niobate. The nonlinear optical response in the nanosecond regime was already studied extensively with a variety of techniques, whereas femtosecond pulses were mainly used in transient absorption or transient grating experiments. Naturally, the temporal resolution of these measurements depends on the pulse duration, however, dynamics during the pulse excitation were barely investigated.
The motivation of this work is to widen the limits of femtosecond spectroscopy, not only to temporally resolve faster nonlinear optical processes, but further to show a sensitivity to other coupling mechanisms between the pulses and the material. Especially, the role of transient, dynamic holographic gratings is investigated with a careful determination of the pulse duration, bandwidth and frequency chirp. A basis of this work is established in the first part by studying the material response via light-induced absorption before focusing on the main topic, the pulse interaction with elementary (holographic) gratings, both self-induced and static, in the second part. By this detailed study, several features of femtosecond laser pulses, holographic gratings and the ultrafast material response can be revealed: (i) grating recording is feasible even with pulses of different frequencies, provided that their pulse duration is sufficiently short, (ii) grating based pulse coupling causes a pronounced energy transfer even in a common pump-probe setup for transient absorption measurements with (non-)degenerated frequencies, (iii) beyond expectation, oscillations in the phonon frequency range become apparent in different measurements. The presented results point towards appropriate future experiments to obtain a more consistent, microscopic model for the ultrafast response of the crystal, involving the interplay between photo-generated polarons, self-induced gratings, and phonons.
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