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<p>The nonlinear interaction between light and atoms is an extensive field of study with a broad range of applications in quantum information science and condensed matter physics. Nonlinear optical phenomena occurring in cold atoms are particularly interesting because such slowly moving atoms can spatially organize into density gratings, which allows for studies involving optical interactions with structured materials. In this thesis, I describe a novel nonlinear optical effect that arises when cold atoms spatially bunch in an optical lattice. I show that employing this spatial atomic bunching provides access to a unique physical regime with reduced thresholds for nonlinear optical processes and enhanced material properties. Using this method, I observe the nonlinear optical phenomenon of transverse optical pattern formation at record-low powers. These transverse optical patterns are generated by a wave- mixing process that is mediated by the cold atomic vapor. The optical patterns are highly multimode and induce rich non-equilibrium atomic dynamics. In particular, I find that there exists a synergistic interplay between the generated optical pat- terns and the atoms, wherein the scattered fields help the atoms to self-organize into new, multimode structures that are not externally imposed on the atomic sample. These self-organized structures in turn enhance the power in the optical patterns. I provide the first detailed investigation of the motional dynamics of atoms that have self-organized in a multimode geometry. I also show that the transverse optical patterns induce Sisyphus cooling in all three spatial dimensions, which is the first observation of spontaneous three-dimensional cooling. My experiment represents a unique means by which to study nonlinear optics and non-equilibrium dynamics at ultra-low required powers.</p> / Dissertation

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In the following work we investigate the dynamics of Bose-Einstein condensates(BECs) under the influence of time-dependent potentials. The response of such a sensitive system to external perturbations is a matter of increasing interest. This is because of the enormous growth in understanding the physics and emerging applications of BECs in many areas of physics such as sensing, microscopy and quantum information.

Since its inception, nuclear magnetic resonance has proved to be a fruitful area of research, and one of the most recent advances is in its application to the imaging of structure within objects. The original technique used, known as projection-reconstruction, is rather sensitive to errors in the magnetic fields and on its own is not practicable for full 3-d imaging, so interest has turned to a number of alternative methods. The technique investigated here, selective excitation, achieves imaging by the use of excitation sequences which can restrict the signal response to chosen regions of a spin sample. In order to make use of the Fellgett advantage, the ideal situation in this case would seem to be to confine excitation to a column of spins from which various properties can then be 'read out' by application of a lengthwise gradient.

The main objective of this work was the development of the existing shock tube system so that it could be used for kinetic investigations. As a result of the many modifications and alterations to the shock tube, and thorough and successful characterisation experiments, the shock tube is now considered to be suitable for the study of high temperature gas phase reactions. One of the important features of the characterisation experiments was the dependency of several shock parameters (P2(expt), P5(expt), and Mr) on the initial test gas pressure in the shock tube. Shock parameters have been determined which take into account non-ideal behaviour such as side wall boundary layer formation. The atomic resonance absorption spectroscopy (ARAS) detection technique was only installed during the latter stages of this work, and due to time restrictions is not yet fully operational. When this is achieved the shock tube at Aberdeen will be the only shock tube in the U.K. where time resolved, gas phase reactions, can be kinetically investigated. Results from Brookhaven National Laboratory, New York, are presented where a similar shock tube - ARAS system was calibrated for atomic oxygen. Nitrous oxide (N2O) was used as a clean source of O atoms, and the bimolecular rate expression for the reaction: N2O + M N2 + O + M. over the temperature range 1266 T(K) 2311 was determined to be: k (cm3molecule-1s-1) = (1.220.19)x10-9 exp (-57861600 cal/RT). This rate expression is in good agreement with literature values.

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Calculations have been performed to obtain accurate cross-sections and thermally averaged rate coefficients for the rotational excitation of methanol by helium, using the Coupled States quantum-mechanical approach. Transitions within the ground and first torsionally excited states of A and E- type methanol were considered. The 'propensity rules' governing the collisional transitions were examined and compared with the results of microwave double resonance experiments. Predictions are made of line intensity ratios which are sensitive to the density of the He perturber and which lend themselves to the determination of the perturber densities in astrophysically interesting regions of molecular clouds.

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