Thesis (Ph. D.)--Physics, Georgia Institute of Technology, 2005. / Rick Trebino, Committee Member ; Philip First, Committee Member ; Chandra Raman, Committee Member ; Ali Adibi, Committee Member ; John Buck, Committee Member. Vita. Includes bibliographical referenced.

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Characterisation of the ultra-short optical pulses produced by infrared ffee-electron lasers (FELs) is an important task, not only for the further development of free electron lasers and their theory, but also for their operation as a research tool. The setting up and optimisation of the FEL requires effective and reliable diagnostics tools. This thesis presents techniques for the measurement of sub-picosecond optical and electron pulses. A range of techniques is developed that allows measurements of the electric field of both optical pulses and electron bunches to be made with an accuracy of better than 100 fs. These techniques have been used to obtain the first complete electricfield characterisation of ultra-short pulses from a far-infrared FEL; to study the formation of singlesided exponential optical pulses in two FELs; and to obtain the longitudinal profile of electron bunches, both by probing the near-field transition radiation and by directly sensing the Coulomb field of the electron bunches. Although the techniques described are not truly single-shot - requiring measurements averaged over a period of a few microseconds - ways in which they could be extended to provide single-shot capability are discussed.

This study determined the key characteristics of temporal patterns of root growth during the crop development period, as well as the vertical patterns of root distribution in the soil profile for important oilseed and pulse crops grown on the semiarid Canadian Prairie. Rooting characteristics greatly influence the nutrient acquisition and water-use patterns for any plants. However, crop root systems have not been studied intensively due to time, labor and costs constraints. In the literature, root studies mostly focus on cereal crops and very limited information is available for oilseeds and pulses even though these broadleaf crops are critical in the diversification of cropping systems. Thus the objectives of this study were to 1) examine the root morphological characteristics, root distribution patterns in the soil profile, and the fine root distributions of oilseeds and pulses in comparison with wheat; 2) to determine the rhizospheric properties of pulse crops. In 2006 and 2007, canola (<i>Brassica napus</i> L.), flax (<i>Linum usitatissimum</i> L.), mustard (<i>Brassica juncea</i> L.), chickpea (<i>Cicer arietinum </i> L.), field pea (<i>Pisum sativum</i>L., lentil (<i>Lens culinaris</i>), and spring wheat (<i>Triticum aestivum</i> L.) were grown under low- (natural rainfall) and high-water (rainfall+irrigation) conditions in southwest Saskatchewan. Roots were sampled at the seedling, early-flower, late-flower, late-pod, and physiological maturity growth stages, and root parameters determined using image analysis. The growth of roots progressed markedly from seedling to late-flowering and then declined to maturity. Root growth of pulse crops was not significantly affected by water conditions, but canola had 70% greater root length, 67% more root surface area, and 79% more root tips under high-water than under low-water conditions. At the late-flower stage, over 70% of the roots in oilseeds and pulses were distributed within the 0-60 cm soil profile and the largest proportion (around 50%) were found in the top 20-cm of the soil depth. About 85% of the roots in oilseeds and pulses were classified as extra fine (diameter <0.4mm). The rhizosphere fungi were significantly different among tested pulses and also pulse rhizosphere fungi were significantly affected by soil depth but not by water conditions. Inoculation of <i>Penicillium bilaiae</i> (product -JumpStart®) to the pulse crops increased the amount of the fungi in their rhizospheres by as much as 42% compared to the pulses not inoculated. Results from this study are novel and provide the baseline for model-related studies on water use and nutrient uptake by root systems of oilseed and pulse crops in semiarid environments.

This study determined the key characteristics of temporal patterns of root growth during the crop development period, as well as the vertical patterns of root distribution in the soil profile for important oilseed and pulse crops grown on the semiarid Canadian Prairie. Rooting characteristics greatly influence the nutrient acquisition and water-use patterns for any plants. However, crop root systems have not been studied intensively due to time, labor and costs constraints. In the literature, root studies mostly focus on cereal crops and very limited information is available for oilseeds and pulses even though these broadleaf crops are critical in the diversification of cropping systems. Thus the objectives of this study were to 1) examine the root morphological characteristics, root distribution patterns in the soil profile, and the fine root distributions of oilseeds and pulses in comparison with wheat; 2) to determine the rhizospheric properties of pulse crops. In 2006 and 2007, canola (<i>Brassica napus</i> L.), flax (<i>Linum usitatissimum</i> L.), mustard (<i>Brassica juncea</i> L.), chickpea (<i>Cicer arietinum </i> L.), field pea (<i>Pisum sativum</i>L., lentil (<i>Lens culinaris</i>), and spring wheat (<i>Triticum aestivum</i> L.) were grown under low- (natural rainfall) and high-water (rainfall+irrigation) conditions in southwest Saskatchewan. Roots were sampled at the seedling, early-flower, late-flower, late-pod, and physiological maturity growth stages, and root parameters determined using image analysis. The growth of roots progressed markedly from seedling to late-flowering and then declined to maturity. Root growth of pulse crops was not significantly affected by water conditions, but canola had 70% greater root length, 67% more root surface area, and 79% more root tips under high-water than under low-water conditions. At the late-flower stage, over 70% of the roots in oilseeds and pulses were distributed within the 0-60 cm soil profile and the largest proportion (around 50%) were found in the top 20-cm of the soil depth. About 85% of the roots in oilseeds and pulses were classified as extra fine (diameter <0.4mm). The rhizosphere fungi were significantly different among tested pulses and also pulse rhizosphere fungi were significantly affected by soil depth but not by water conditions. Inoculation of <i>Penicillium bilaiae</i> (product -JumpStart®) to the pulse crops increased the amount of the fungi in their rhizospheres by as much as 42% compared to the pulses not inoculated. Results from this study are novel and provide the baseline for model-related studies on water use and nutrient uptake by root systems of oilseed and pulse crops in semiarid environments.

Due to the large penetration depth in tissues, ultra-broadband supercontinuum (SC) in the 1m wavelength range, which is regarded as a diagnostic window in bio-photonics, represents a versatile light source for a wide range of bio-imaging and spectroscopy applications. In particular, dispersive Fourier transform (DFT) has recently emerged as anultrafast optical technique forimaging and spectroscopy. Thus, In order to employ the SC source for DFT, it has to exhibit ultra-broad bandwidth as well as good temporal stability– the two important metrics for practical high-speed bio-imaging and spectroscopy applications. In this thesis, we first demonstrate stabilized and enhanced SC generation (in the anomalous dispersion regime) at 1m by a minute continuous-wave (CW) seeding scheme. By introducing a weak CW which is around 200,000 times weaker than the pump, a significant broadening in the SC bandwidth and an improvement in the temporal stability is obtained. This seeding scheme allows, for the first time,1m DFT at a spectral acquisition rate of 20MHz with good temporal stability-paving the way toward realizing practical real-time, ultrafast biomedical spectroscopy and imaging. For the DFT part, instead of using the regular specialty 1m single mode fiber (SMF) as the dispersive elements, we here explore and demonstrate the feasibility of using the standard telecommunication single-mode fibers (e.g. SMF28 and dispersion compensating fiber (DCF)) as few-mode fibers (FMFs) for optical time-stretch confocal microscopy in the 1m region. By evaluating group velocity dispersion (GVD) of different FMF modes and thus the corresponding time-stretch performances, we show that the fundamental modes (LP01) of SMF28 and DCF, having sufficiently high dispersion-to-loss ratios, are particularly useful for practical time-stretch spectroscopy and microscopy in the 1m region, without the need for the specialty 1m(single mode fiber) SMF. More intriguingly, the ability of selective modal excitation in FMFs also enables us to utilize the higher-order FMF modes (e.g. LP11) for time-stretch imaging. Such additional degrees of freedom create a new avenue for optimizing and designing the time-stretch operations, such as by tailored engineering of the modal-dispersion as well as the GVD of the individual FMF modes. In the search for stable and efficient SC generation for practical bio-imaging and spectroscopy, we also numerically investigate the active enhancement of the seeded-SC generation pumped in the normal dispersion regime. Similarly, we introduced a minute CW seeding scheme, more specifically seeding spectrally coincides with the Raman gain peak of the pump. With this design, the SC bandwidth can be enhanced to more than one octave, even when the pump is far away from zero dispersion wavelengths (ZDW) (~100nm) in the normal dispersion regime. This new seeding mechanism opens opportunities to expand the scope of active seeding mechanism for enhancing SC generation to the normal dispersion regime. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Thesis (MSc)--University of Stellenbosch, 2008. / Bibliography. Also available via the Intenet.