The multi-pass ring cavity was constructed using only a pair of identical spherical mirrors, which is compact and can easily be aligned. The spatial hole burning effect and green problem can be eliminated in these ring cavities that can be applied to generate a single frequency laser. The characteristics of multi-pass non-planar and planar multi-pass ring cavities were analyzed, such as the reentrant conditions and cavity stability. The multi-pass ring lasers were successfully demonstrated by the reentrant condition simulations, the cavity length error between experimental result and simulation value were below 1.2%. Yb3+:YAG was used as the gain medium in this dissertation, it has many advantages compared with that of Nd3+:YAG. Such as high doping concentration, low quantum defect, long upper state lifetime, broad emission bandwidth and its wide absorption band. However, the quasi-three-level nature of Yb3+:YAG makes temperature control crucial for laser performance. A Ti:sapphire laser pumped Yb3+:YAG bulk crystal multi-pass continuous-wave ring laser was demonstrated with a slope efficiency of 50.3%, and a Yb3+:YAG crystal fiber ring laser was demonstrated with a slope efficiency of 54.7%. The thermal load in Yb3+:YAG was observed and compared with that of Nd3+:YAG. The passively Q-switched operation was obtained by a Cr4+:YAG saturable absorber. Due to the ring cavity configuration, the spontaneous noise from gain medium perturbs the population difference of the saturable absorber was reduced so that the timing jitter of the repetition period was restrained to around 11% while 33 ns pulses were obtained. A compact diode-pumped continuous-wave ring cavity with 25.0% slope efficiency was presented. Two main challenges are noticed in the high power laser diode end pumped configuration, mode-matching difficulty and huge heat load. The mode-matching problem can be solved by an appropriate cavity design, the laser-heated pedestal growth (LHPG) method was used to growth Yb3+:YAG crystal fiber with small surface to improve the heat dissipation. The fiber crystal laser was successfully generated and compared with that of bulk crystal. To our knowledge, this is the first demonstration of a Yb3+:YAG ring laser, and also the first demonstration of Yb3+:YAG crystal fiber ring laser.

Zugl.: Darmstadt, Techn. Univ., Diss., 2007

This paper examined a few different types of interacting galaxies and the implications the data has on cosmological theories. An analysis of the Holmberg Effect, Holmberg (1969)’s observation that companion galaxies tend to be near the poles of edge-on galaxies rather than in the planes, was done by reexamining the spirals viewed by Holmberg. Only using radial velocity confirmed companions to test for this effect showed that if anything, the opposite of the Holmberg effect is true. However, due to small number statistics, more edge-on spirals and their companions would have to be viewed in order to determine if this is an actual physical effect of anisotropic companion distribution around primary galaxies. It is important to discover if there is a preferred distribution, because it could point to the distribution of dark matter around the primary galaxies, and have interesting impacts on large-scale universal structure and cosmology theory.

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A number of amino acids containing terminal five- and six-membered heterocyclic substituents have been synthesised using a strategy in which a 6-oxopipecolate system is 'ring switched'. Functionalisation of the protected (2S)-6-oxopipecolate at C-5 with methyl formate, or with allyl bromide followed by ozonolysis, have provided the important 5-formyl-6-oxopipecolate and its' homologue as intermediates. Reaction of these intermediates with hydrazine gave a successful 'ring switching' reaction, yielding a pyrazolone and a pyridazin-6-one, which were deprotected to give the free amino acids. Alkylation of the homodehydro-6-oxopipecolate system at C-4 by Michael addition with allyl cuprate, followed by ozonolysis, provided the important 4-formyl-6- oxopipecolate intermediate. Reaction with hydrazine gave a successful 'ring switching' reaction yielding a pyridazin-6-one, which was deprotected to the free amino acid. Attempts to apply the 'ring switching' reaction to morpholinones, thiazanes, azepanes, thiazepines and were unsuccessful. The amino acids synthesised are currently being examined in a high throughput screen at Glaxo-Wellcome

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