Thesis (Ph.D.(Chemistry))--University of Pretoria, 2009. / Includes abstract in English. Includes bibliographical references. Also available online.

D.Tech. (Biomedical Technology) / Stem cells are defined as undifferentiated cells that can proliferate and have the capacity of both self-renewal and differentiation to one or more types of specialised cells (Bishop et al., 2002). The two types of stem cells are embryonic and adult stem cells. Adult stem cells have been isolated from adipose tissue in abundance and with ease (Mvula et al., 2010) and these cells have been differentiated into smooth muscle cells (SMCs) with the enhancement of low intensity laser irradiation and the growth factors (de Villiers et al., 2011). Smooth muscles play an important role in diseases like cancer, hypertension, asthma and others (Rodriguez et al., 2006). Studies have shown that low intensity laser irradiation (LILI) can increase proliferation of cells, cellular attachment, differentiation and production of transforming growth factor-beta 1 (TGF-β1) in cells indicating that in vitro LILI can modulate the activity of cells and tissues (Khadra et al., 2005). Further studies have also discovered that LILI enhances wound healing (Fiszerman and Markmann, 2000). LILI has been successfully used for pain attenuation and to induce wound healing in non-healing defects (Hawkins and Abrahamse, 2005). LILI has been shown to increase viability and proliferation of adipose derived stem cells (ADSCs) (Mvula et al., 2008 and Mvula et al., 2010). Growth factors such as retinoic acids (RA) have been shown to have major influences on cells. They are involved specifically in apoptosis, cell proliferation, differentiation and maturation (Duong and Rochette, 2011; Gudas and Wagner, 2011). Co-culturing is used to achieve several cellular processes including proliferation, differentiation and migration (Kim et al., 2012). When two types of cells are cultured together, they are exposed to a number of complex environmental factors such as cytokines, extracellular matrix components, cell interactions, mechanical stimuli, signalling transcriptional pathways and transcriptional factors such as growth factors. v These factors are able to affect migration, proliferation and differentiation of one cell type into another (Zhang et al., 2012). The aim of this study was to investigate the differentiation potential of ADSCs when co-cultured with (SMCs) and to determine the role of LILI on the co-cultured cells. Short and long term biological effects were monitored on these cells following exposure to LILI and addition of growth factors. The study used commercial and isolated human ADSCs and SMCs (SKUT-1) cells. After growing cells to semiconfluency for ADSCs and confluency for SMCs, they were co-cultured in a ratio of 1:1 using the established methods supplemented with and without growth factors (TGF-β1and RA) and then exposed to LILI. The cellular morphology, viability and proliferation activities of the irradiated cells were then assessed using direct inverted and differential interference contrast microscopy (DIC), trypan blue test, adenosine triphosphate luminescence, optical density analysis, and carboxyfluorescein diacetate succinimdyl ester (CFSE) methods. In particular the expression of the specific markers of both ADSCs, β1 Integrin (CD29) and Thy-1 (CD90) and SMCs, Myosin Heavy Chain (MHC) were investigated through immunoflourescent microscopy and flow cytometric analysis. Up and down regulation of genes involved in the human mesenchymal stem cell array were analysed through Reverse Transcriptase Polymerase Chain Reaction (RTPCR)...

This dissertation documents the development and demonstration of a new laser crystallization process called spot-beam annealing (SBA). The SBA method is a partial-melting-based laser-annealing method, which converts as-deposited amorphous Si films into high-mobility TFT-enabling polycrystalline films. SBA builds on the thermally additive utilization of multiple short-lived low-energy ultra-high-frequency pulses, achieved via substantially overlapped scanning of a small spot beam to incrementally and gradually heat and partially melt the beam-irradiated region. After a brief review of other laser crystallization technologies, the conceptual framework for the SBA process is introduced, and various possible implementation schemes and development paths are discussed. In the present work, the SBA method is implemented using a new class of ultra-high-frequency (>100 MHz), low-pulse energy (<1 𝜇J), short-pulse-duration (<1 ns) UV fiber lasers. The first half of the thesis (chapters 4 and 5) presents, the simulation- and calculation-based studies of the SBA process. A simple but relevant one-dimensional thermal analysis identifies the "dwell time" (associated with the overall intensity temporal profile defined by the collection of those pulses that irradiate a point in the film) as a key SBA parameter. Provided that a sufficient number of multiple shots are involved in irradiating the point in the film, this parameter dictates the overall thermal and transformation cycle of heating, primary melting, and solidification that enables the ultra-short-pulse-based SBA method to mimic the physical conditions encountered previously only using pulsed lasers with pulse duration in the range of tens to hundreds of nanoseconds; the precise range needed for optimally generating laser-annealed polycrystalline materials on glass and plastic substrates. Additionally, we also identify and examine an important differentiating feature of the SBA method, namely the highly transient temperature spikes that arise from the individual pulses incident onto a point on the film during overlapped scanning. By simultaneously considering the preliminary experimental results that are presented in this thesis (chapters 6 and 7), we suggest that these periodic temperature spikes, the specific degree of which depends on the temporal profile and energy density of individual pulses, can potentially play a key role in dictating certain important details of melting and solidification transitions encountered in SBA. In particular, we identify and elaborate on how the temperature fluctuations can affect how explosive crystallization of a-Si films is manifested in a different manner than has previously been observed. In addition, we point out how the fluctuations can control the degree to which the melting scenarios in SBA can deviate from the grain-boundary-melting-dominated 2-D transition scenario (as for instance encountered in pulsed-laser irradiation of columnar-grained polycrystalline films), where lateral melting is exclusively initiated at grain boundaries and propagates predominantly laterally into the superheated and defect-free interior of the grains. In the second half of the thesis, the experimental results that are obtained from a recently constructed research SBA system are presented, characterized, and evaluated. Specifically, the examination of single-scan and multiple-scan exposed Si films conducted using OM, AFM, and TEM material characterization techniques reveals that the method is capable of not only generating uniform polycrystalline Si films consisting of ordered grains with tight grain-size distribution around the beam wavelength, but it can furthermore be configured to produce polycrystalline films with an enhanced level of ordering as manifested in the films with a highly parallel ridge (HPR) pattern.

The equations tor the propagation of Electromagnetic and Optical waves in tapered fibers and metallic waveguides are derived. Solutions are derived for the displacement of the beam from the waveguide axis as a function of distance along the axis, and also tor the beam width as a function of distance. These equations are solved numerically for a variety of tapered guides. Experiments are conducted which verify the theoretical results.

High power lasers with diffraction limited beam quality are desired for many applications in defense and manufacturing. A lot of applications require laser beams at the 100 kW power level along with divergence close to the diffraction limit. The figure of merit for a beam used in such applications should be radiance which determines the laser power delivered to a remote target. One of the primary limiting factors is thermal distortion of a laser beam caused by excessive heat generated in the laser media. Combination of multiple laser beams is usually considered as a method to mitigate these limitations. Spectral beam combining (SBC) by volume Bragg gratings (VBGs) is a very promising method for the future of high radiance lasers that needs to achieve 100 kW-level power. This work is dedicated to development of methods to increase spectral density of combined beams keeping their divergence at an acceptably low level. A new figure of merit for a beam combining system is proposed, the Beam Combining Factor (BCF), which makes it possible to distinguish the quality of the individual beams from the quality of beam combining. Also presented is a method of including the effect of beam divergence and spectral bandwidth on the performance of VBGs, as well as a method to optimize VBG parameters in terms of thickness and refractive index modulation for an arbitrary number of beams. A novel thermal tuning technique and apparatus is presented with which the SBC system can be tuned for peak efficiency from low to high power without the need for mechanical re- iv alignment. Finally, a thermally tuned SBC system with five beams, with a spectral separation between beams of 0.25 nm at a total power of 685 W is presented. The results show the highest power spectral density and highest spectral radiance of any SBC system to date. Recent demonstrations in SBC by multiplexed VBGs and the use of super Gaussian beams for beam quality improvement are also discussed.

No description available.

One of the negative effects that a laser beam experiences as it propagates through the atmosphere is intensity fluctuations or scintillation. Because scintillation-- as it pertains to laser radar and laser satellite communication systems-- is the main subject of this research, the assumption of an optical element ( such as a Gaussian lens) along the propagation path in front of the detector is valid. The mathematical addition of optical elements to the propagation path is treated using the ABCD ray matrix method. The expression for scintillation is derived, analyzed, and numerically calculated for positions to the left and right of the image plane, which is behind the collecting lens of a receiver system. Simultaneously, the behavior of the scintillation is investigated when the aperture size of the lens is increased. The results are compared to the aperture averaging effect experienced when the beam is in the image plane. This is a per-unit scintillation decrease because the aperture averages it over the surface of the lens.

An experimental and a theoretical analysis for a laser beam propagating through multiple phase screens was performed. The theoretical analysis showed that the statistics for the intensity fluctuations, which can be predicted by the HK and the I-K distributions, could be derived from a multiplicative process using statistical distributions derived from Gaussian statistics. For the single phase screen experiment, the experimental normalized moments were compared with the normalized moments of both the HK and I-K distributions . In addition, the intensity data was lowpass filtered to yield moments that are predicted by the gamma distribution. The single phase screen data was segmented into small time intervals, and all time segments with approximately the same variance were grouped together into bins to yield normalized moments for each bin that are predicted by the Rician distribution. Also, the normalized moments for two and three phase screen experiments were measured. Finally, a computer program was written to simulate K distributed noise from two independent Gaussian noise sources.

Processing and analysis routines giving normalized moments of optical intensity, structure functions of wind velocity and temperature, central moments, and various measures of the turbulence parameter, C2N, are presented. Rapid analog-to-digital data conversion and storage to implement this analysis using MINC 11/23 with RT11 operating system are discussed. Coding for file organization and implementation of processing routines on the VAX 11/750, VMS operating system are also discussed.

No description available.