Inaug. Diss.--Eberhard-Karls-Universität, Tübingen.

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Thesis (D.M.A.)--University of Oklahoma, 1993. / Includes bibliographical references (leaves 296-306).

No description available.

This dissertation is on the development of a laser system for the generation of femtosecond frequency combs in the vacuum-ultraviolet (VUV) via intracavity high-harmonic generation (HHG). The HHG process yields coherent vacuum ultraviolet (VUV) light resulting from the ionization of noble gases driven by intense near-IR femtosecond frequency combs in an optical enhancement cavity. An injection locked amplification cavity (fsAC) was developed in order to generate a high power femtosecond frequency combs based on a Ti:Sapphire oscillator. Detailed amplifier performance was investigated in order to evaluate the coherence of the pulse amplification process. A passive power enhancement cavity for fs pulses (fsEC) was designed for intracavity high harmonic generation. For maximum power enhancement and conversion efficiency, the intracavity dispersion was compensated and various design layouts tested. A careful analysis of the phase matching conditions was performed, taking into account the effect of reabsorption of the generated high harmonic light, to compare different cavity geometries and determine which would produce the most efficient harmonic yield. Numerical simulations were also performed to determine the level of intra-cavity ionization that could be sustained before disrupting the pulse enhancement process. Based on the results of these simulations and calculations, it was determined that for a xenon gas target, a moderate peak intensity of the order of ~ 5×10¹³W/cm² produces harmonics most efficiently.

Atramines sienas (toliau – AS) veikia įvairios apkrovos dėl kurių susidaro neleistinos deformacijos, atsiranda plyšiai, atraminės sienos pasvyra, siekiant jas apsaugoti nuo tolimesnio svyrimo ir griūties AS būtina stiprinti. Remiantis literatūros apžvalga pastebėta, kad nėra detaliai aptarti žemutinio bjefo (toliau – ŽB) atraminių gelžbetoninių (toliau – g/b) sienų stiprinimo būdai, todėl detalesniems tyrimams pasirinkti 4 hidromazgai (toliau – HTS), kurių atraminėms sienoms reikalingas stiprinimas. Darbo tikslas – įvertinti tinkamiausią gelžbetoninių atraminių sienų stiprinimo išramstant būdą. Siekiant parinkti tinkamiausią išramstymo būdą atlikti palyginamieji ekonominiai bei konstrukciniai skaičiavimai. Pagal ekonominių ir konstrukcinių skaičiavimų rezultatus nustatyta, kad ekonomiškiausias išramstymo būdas – įrengiant monolitines sijas ir „šukas“. / Retaining walls are under the influence of a number of loads, which results in unacceptable deformation, cracks appear and load-bearing walls lean on one side. Retaining walls should be strengthened in order to protect them from further collapse and loping. According to literary review, it is noticed that there is no detailed analysis of the lower pool retaining angled reinforced concrete wall-building techniques. This was the reason why 4 hydroschemes were chosen for more detailed researches in order to determine which retaining walls need strengthening. The aim of this work is to assess the most appropriate angled retaining wall building method. In order to select the most appropriate way of strengthening, comparative economic and structural calculations are done. In accordance with economic and structural results of calculations, it is found that the most economical way of building is a monolithic installation of beams and “combs”.

The University of Gotland has between the years 2006-2011 conducted seminar excavations in Västergarn parish, Gotland. During this time 167 comb fragments have been registered. Out of these are 51 of importance for this study, since they are defined as either a single-sided composite comb or a comb case. The purpose of this thesis is to enlighten the earliest period in the history of Västergarn by focusing on the earliest forms of combs and their cases. And as the title expresses do the combs date to the Viking Age or the Middle Ages? The combs from the excavations will be compared to different type schemes, both Viking Age and Middle Age and different places in Scandinavia such as Lund, Oslo, Lödöse and Gotland. The conclusion of the analysis is that the combs from Västergarn are from the late 11th century to the early 13th century, during the Early Middle Age.

Optical frequency combs have resulted in significant advances in optical frequency metrology and found wide application to precise physical measurements and molecular fingerprinting. A direct analogue of frequency combs in the phononic or acoustic domain has not been reported to date. This thesis describes a series of results to provide the first clear evidence for the generation of phononic frequency combs in the domain of micromechanical resonators. These results are supported by a theoretical framework which was originally developed to predict the existence of such features of combs in physical systems described by Fermi-Pasta-Ulam dynamics. The phononic frequency combs is mediated by nonlinear coupling between a primary driven mode and one or more parametrically excited internal modes. We provide experimental evidence for the formation of such phononic frequency combs in systems comprising of 2 or more coupled modes, with results qualitatively consistent with previous numerical studies based on Fermi-Pasta-Ulam dynamics. Additionally, externally pumped comb processes are also reported. Through systematic experiments at different drive frequencies and amplitudes, we portray the well-connected processes of phononic frequency comb formation and define attributes to control their concomitant features. Further, the interplay between these new nonlinear resonances and the well-established Duffing phenomenon is also discussed. While the experimental verification of the existence of phononic frequency combs is of scientific interest, several potential engineering applications exist including the unique capability to track resonant frequency of a micromechanical resonator without the requirement for an external feedback loop to sustain oscillations at the resonant frequency. The initial experimental results also demonstrate that good short-term frequency stability may be obtained for such micromechanical resonators operated under ambient conditions.

<p>Optical beam steering is of significant importance for various emerging applications such as light detection and ranging (LiDAR), free space optical communication, and holographic display. However, the development of schemes for dynamic spatio-temporal beam steering has been limited in the past. A previous study achieved dynamic and continuous angular beam steering of isolated ultrashort pulses from a mode-locked laser by using a passive metasurface emulating a diffraction grating followed by a lens. In this thesis, we experimentally demonstrate dynamic spatio-temporal steering of high repetition rate pulse trains using a spatial array of frequency combs with a uniform gradient in their carrier-envelope offsets. To accomplish this, we leverage the capabilities of a virtually imaged phased array (VIPA), which is a side-entrance Fabry-Perot etalon, and employ successive spatial Fourier transforms facilitated by a 4f optical lens system. Our experimental results successfully demonstrate the periodic scanning of ultrashort pulse trains generated from an electro-optic comb at a repetition rate of ~10 GHz. The scanning occurs in discrete steps of ~115 μm and ~20 ps in the spatial and temporal domains, respectively.</p>

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