Zugl.: Braunschweig, Techn. Univ., Diss., 2009

Thesis (M.S.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains vi, 101 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 41-45).

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 145-154). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (p. 138-155).

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references (leaves 97-103). Available also in a digital version from Dissertation Abstracts.

Thesis (M. Phil.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 111-114).

A lower limb prosthesis provides assistance to its user in both ambulation and stationary support. The lower limb prosthesis consists of a socket, which interfaces with the residual limb, a pylon, attachment hardware to secure the pylon to the socket, and a prosthetic foot. For the prosthesis to be effective, the socket must be comfortable, functional and aesthetically appealing, usually in that order. Lack of comfort and fit can cause movement problems and health issues. The residual limb of the amputee changes its volume throughout the day and in order to maintain comfort a socket must be able to adapt to these volume changes. Previous research has resulted in the development of concepts for inflatable prosthetic sockets capable of addressing this need. The concepts rely on laser sintering (LS) to manufacture the parts. This research focuses on the development of a finite element analysis (FEA) method to assist in the design of adaptive sockets. The FEA can be used to predict the pressure-deflection curve of a given socket design. The FEA method was verified by experiments using LS manufactured test specimens. Results from FEA simulations indicate that the LS-manufactured sockets will achieve the desired deflection (~0.1 in) for relatively low pressures (< 10 psi), providing evidence for the feasibility of this approach. / text

An intense laser or charged particle pulse propagating through matter excites light-speed refractive index structures in its wake via Kerr effect, ionization, or displacement of electrons from background ions. Examples include plasma wakes used to accelerate charged particles and self-guided filaments used for atmospheric analysis and micromachining. Such applications constrain the shape, size and evolution of the index structure, yet often these are known in detail only through intensive computer simulations based on estimated initial conditions. Here we develop and demonstrate three methods for visualizing evolving light-speed structures directly in the laboratory in a single shot : (1) frequency-domain streak camera, (2) frequency-domain tomography, and (3) multi-object-plane phase-contrast imaging. All three methods are based on analyzing phase perturbations that an evolving object imprints on one or more probe laser pulses that cross its path obliquely. The methods are tailored to different propagation lengths, material densities, and dimensionality of imaging. Using these techniques, evolving laser-driven filaments in glass and air and plasma wakes in helium gas driven by laser pulses up to petawatt peak power are visualized in one shot, revealing underlying nonlinear laser-plasma interaction physics that is compared in detail to computer simulations. / text

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

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