Highly energetic ultrafast pulses are necessary for many applications including, but not limited to, nonlinear microscopy, pump-probe spectroscopy, mid-IR generation, micromachining and even optical data storage. A preferred source for such applications would be a highly energetic, fiber-based, color-tunable source capable of providing multi-color time-synchronized pulses with minimal relative timing jitter, on demand. Conventional free-space sources based on bulk parametric nonlinearities are capable of providing highly energetic ultrafast pulses of tunable wavelengths, however they lack the robustness and remote delivery that fiber-based sources readily provide, and may also suffer from lack of temporal synchronicity and spatial collinearity of multi-color outputs. Notable fiber-based solutions that attempt to alleviate some of these shortcomings include soliton self-frequency shifting (SSFS), parametric oscillation and self-phase modulation (SPM) enabled spectral selection. Such techniques can yield dual-color sources with some success, however they are not capable of providing temporally synchronized dual-color or multi-color pulses on their own; because group velocity dispersion prevents time-synchronization between the pulses of different colors. Even if temporal and spatial overlap is achieved through external means; which defeats the purpose of using fibers, such sources may suffer from relative timing jitters on the order of the pulse durations themselves due to effects such as temperature, stress, pump power fluctuations culminating upon pulse propagation over long transmission lengths in fibers. We study a recently discovered process called soliton self-mode conversion (SSMC), providing a power scalable platform for the generation of ultrafast pulses at userdefined colors. SSMC is an intermodal ultrafast Raman process which relies on the dispersion - and hence group index - diversity of higher order modes in multimode fibers. During the mode conversion process, the two participating modes at their respective wavelengths share the same group index, thus circumventing the temporal walk-off of the two pulses at distinct wavelengths. It has been shown that one can obtain pulses up to 80 nJ pulse energy (74 fs pulse width) with the SSMC process, as well as creating temporally locked dual-color pulses when the process is stopped mid power transfer. In this thesis, we aim to understand the SSMC process by studying its fundamental properties and characteristics, in order to be able to exploit them to obtain ultrafast color-tunable sources with multi-color temporally locked output pulses. We first investigate the pulse-to-pulse coherence properties of SSMC-created pulses through interferometric techniques, which reveal it to be a spontaneous process. Crucially we find that SSMC can be the dominant ultrafast process in a fiber even in the presence of other nonlinear pathways (of which, plenty exist in multimode fibers) despite the fact that it is strictly quantum noise initiated. Hence, SSMC is a robust nonlinearity that may be easily controllable by dispersion engineering of fibers and their modes. Another aspect of SSMC that we probe is its manifestation in the face of chirping of the input pulse. We show that we can use chirp control as a method to tune the output wavelength over a range of ∼250 nm, with ∼30 nJ pulse energies. Although we can access broad wavelength tunability with the SSMC process, it results in an inherent gap in the wavelength tuning range, owing to the fact that during the mode conversion the wavelength separation between the two modes is about one Stokes shift. We show that by taking advantage of the distinct outcomes the two signs of chirp provides, we can decrease this inaccessible region by half, leaving only∼ 30 nm (about half a Stokes shift) of gap over the tuning range. Lastly, we leverage the group index matching condition for SSMC to induce threecolor and four-color SSMC pulses, increasing the largest available frequency separation between pulse pairs to ∼25 THz with the three-color and to ∼35 THz with the four-color SSMC schemes. Nonlinear mixing experiments conducted on each pair (of the multicolor set of pulses) reveal that the multi-color SSMC process yields timelocked pulses as well. The three color pulses were each measured to have ∼6.5 nJ pulse energy and ∼95 fs pulse width, while the four color pulses were ∼5 nJ and ∼100 fs. We demonstrate that through selection of fiber size, length and launch mode, we can generate multi-color, time synchronized pulses through SSMC, directly out of a single aperture on demand. Hence, we show that multimode fiber-based SSMC yields a versatile platform to generate tunable single-color as well as multi-color jitter free ∼ 100 fs pulses at high energies (∼10s of nJ) directly out of optical fibers.

The present work is concerned with methods of finding the energy eigenvalues of the one-particle Schrödinger equation for various model potentials in one, two, three and N-dimensional space. One major theme of this thesis is the study of diverent Rayleigh-Schrödinger perturbation series which are encountered in non-relativistic quantum mechanics and on the behaviour of the series coefficients E(n) in the energy expansion E(λ):E(O)+∑ E(n)λⁿ. Several perturbative techniques are used. Hypervirial and Hellmann-Feynman theorems with renormalised constants are used to obtain perturbation series for large numbers of potentials. Pade approximant methods are applied to various problems and also an inner product method with a renormalised constant is used to calculate energy eigenvalues with very high accuracy. The non-perturbative methods which are used to calculate energy eigenvalues include finite difference and power series methods. Expectation values are determined by an approach based on eigenvalue calculations, without the explicit use of wave functions. The first chapter provides a glance back into history and a preview of the problems and ideas to be investigated. Chapter two deals with one dimensional problems, including the calculation of the energy eigenvalues for quasi-bound states for some types of perturbation (λx²ⁿ⁺¹). Chapter three is concerned with two, three and N-dimensional problems. Chapter four deals with non-polynomial potentials in one and three dimensions. The final chapter is devoted to a variety of eigenvalue problems. Most of the energy eigenvalues are computed by more than one method with double precision accuracy, and the agreement between the results serves to illustrate the accuracy of the methods.

<p> The home built Magneto-Optical Kerr Effect (MOKE) microscope was implemented to probe the magnetic domain patterns of thin film samples. A CCD camera is introduced to the existing MOKE rotation measurement setup. The images captured by the camera are used to analyze the change in the magnetic domain patterns by the Kerr effect. Using 6.5&times; zoom lens and 1.33&times; extension tube attached to the CCD camera, the size of the sample down to a 1.02mm by 0.75 mm area can be viewed in the image capture. Magnetic hysteresis loop is first measured to investigate the magnetic switching behavior and measure the coercivity. Domain images that exhibited the most significant change were mostly captured between magnetic remanence and near coercivity. The images of samarium cobalt thin film at or near magnetic coercivity showed the changes in shape and light intensity of the magnetic domain light patterns due to the Kerr rotation.</p><p>

<p> Magnetic Force Microscopy (MFM) is a viable method of analyzing magnetic characteristics of ferromagnetic nanostructure materials. The nanosphere template produces a variety of magnetic domains for the endeavor of advancing technological applications such as nanomagnetic logic and magnetoplasmonic nanoparticles. These nanomagnetic applications demand very specific magnetic characteristics, so the profiling of different magnetic domains using magnetic force microscopy is essential. During this work, we studied the magnetic domains that came from permalloy material on nanosphere templates. We investigated the most optimal MFM scan parameters that could produce a viable and trustworthy magnetic domain image. After analyzing two types of samples with different nanosphere template arrangements scanned at two scan angles, 0&deg; and 90&deg;, relative to the cantilever, it was concluded that both scan angles produced optimal images. The optimal lift scan height, relative to the sample surface, was determined to be 65 nm away, where the magnetic domain is most accurately observed. When the tip magnetization was reversed, the MFM images show a corresponding flipping of the magnetic domain characteristics, but maintained the domain size and pattern. Further research is needed to determine the cause of magnetic domain ripples that appear in images.</p><p>

In this thesis investigations of short pulse XeCl, KrF and ArF excimer lasers and HF laser transmission in fused silica and fluoride glass fibres respectively are reported, together with studies of polymer and soft tissue ablation in air and saline. Etch rate and photoacoustic measurements have been used to study the ablation process for the tissue and polymer samples with excimer lasers. The main emphasis is on the HF laser where a UV preionized transverse discharge in SF6 - C3H8 mixtures was used to generate ≃400ns (FWHM) pulses of energy up to 380mJ. Transmission measurements made on a 500μm core diameter fluoride glass fibre gave a distributed loss coefficient of −3 1.5x10 cm−1, and a maximum useful input fluence of ≃15Jcm−2 set by non-linear loss at the fibre input surface. For bovine cornea in air the onset of ablation occured at a fluence of ≃0.5Jcm−2, removal rates increased slowly up to ≃3Jcm−2 but above this increased sharply, reaching ≃17μm per pulse at 8Jcm−2. In saline the interaction becomes considerably more complicated because strong-heating of water at the fibre tip leads to the formation of a hot, high pressure vapour cavity (optical cavitation). Under these conditions the damage range may extend well beyond the beam penetration depth as a result of flow effects (eg. jetting) and intense acoustic emission associated with the 'bubble' growth and collapse. The dynamics of cavitation 'bubbles' have been investigated using pulsed dye laser shadowgraphy for various fibre-tissue geometries and results in free liquid modelled using the Rayleigh-Plesset theory. Time resolved photoacoustic measurements have also been made and revealed that very large transient pressures are generated in tissue near the fibre tip when ablation occurs in liquid; for example, at 8Jcm−2, B peak pressures reached about 1.5x108Pa. When the fibre-to- sample spacing was varied physical surface damage was evident out to distances of ≃250μm for cornea and ≃2mm for retina. As these are much greater than the characteristic beam absorption length in water (≃1.6μn), the main damage mechanism is then not through photoablation but jetting or acoustic emission associated with optical cavitation.

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"Major Subject: Applied Physics" Title from author supplied metadata (automated record created 2010-03-12 12:08:51). Includes bibliographical references.

<p> Efficiency of solar cells is degraded by deposition of mineral dust as well as other particles, and experiments reveal that losses can be significant (up to ~85%) depending on various factors. However, little is known about the role of light scattering and absorption in reducing optical transmission to the solar cell semiconductor. This dissertation first develops a fundamental model of optical losses due to particle-on-substrate scattering for light propagating into the forward direction. We use discrete dipole approximation with surface interaction (DDA-SI), which is a numerical solution of light scattering for an arbitrarily shaped particle-on-substrate. Using DDA-SI, we studied transmission losses due to hemispheric backward scattering (HBS) and absorption. A parameter called the fraction of power lost, defined as the ratio of HBS efficiency plus absorption efficiency to extinction efficiency, was found appropriate to describe optical losses into the forward direction. We found that fine particles lead to higher losses (per optical depth or layer optical thickness) than coarser ones. Losses into the forward direction are maximized when the ratio of skin depth to particles diameter approaches unity. </p><p> In addition, we conducted a resuspension-deposition experiment with two types of mineral dust, optically absorbing and non-absorbing dust. The dust samples were suspended and deposited onto glass slides, acting as surrogates for solar cells. Dust-deposited glass slides with increasing amounts of mass per area were spectroscopically characterized using a spectrophotometer with an integrating sphere (SIS) detector system. The SIS device allowed us to measure forward-hemisphere scattering, HBS, and direct beam transmission. Transmission into the forward direction was found to decrease as function of optical depth, depending on the absorptivity of the dust. Multiple-scattering radiative transfer theory, specifically the two-stream model as well as Monte Carlo stochastic calculations, were used to describe transmission as function of optical depth for both absorbing and nonabsorbing dust, yielding good agreement with experimental results within ~5%. Two-stream model and Monte Carlo techniques yield a multiple-scattering transmission calculation that depends on the single-scattering parameters of albedo and asymmetry parameter. </p><p> This study has the potential to help with solar energy forecasting, aiding smart power grids in predicting and adapting to variations in solar cell energy output due to aerosol deposition. In addition, this study can help optimize cleaning procedures and schedules to save water in desert and semi-arid regions by describing transmission losses as function of dust type. </p><p>

<p> The water vapor concentration plays an important role for many atmospheric processes. The mean concentration is key to understand water vapor's effect on the climate as a greenhouse gas. The fluctuations about the mean are important to understand heat fluxes between Earth's surface and the boundary layer. These fluctuations are linked to turbulence that is present in the boundary layer. Turbulent conditions are simulated in Michigan Tech&rsquo;s multiphase, turbulent reaction chamber, the &Pi; chamber. Measurements for temperature and water vapor concentration were recorded under forced Rayleigh- B&eacute;nard convection at several turbulent intensities. These were used to calculate the saturation ratio, often referred to as the relative humidity. The fluctuations in the water vapor concentration were found to be the more important than the temperature for the variability of the saturation ratio. The fluctuations in the saturation ratio result in some cloud droplets experiencing a higher supersaturation than other cloud droplets, causing those "lucky" droplets to grow at a faster rate than other droplets. This difference in growth rates could contribute to a broadening of the size distribution of cloud droplets, resulting in the enhancement of collision-coalescence. These fluctuations become more pronounced with more intense turbulence.</p><p>