<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>

<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>

<p> We provide estimates of both cross section and rate for the stimulated attachment of a second positron into the (1<i>s</i>² ¹<i>S^e</i>) state of the <i>H&macr; </i>⁺ ion using Ohmura and Ohmura&rsquo;s (1960 Phys. Rev. 118 154) effective range theory, Reiss&rsquo;s strong field approximation (1980 Phys. Rev. A 22, 1786), and the principle of detailed balancing. Our motivation for producing <i>H&macr;</i>⁺ ion include its potential to be used as an intermediate state in bringing antihydrogen to ultra-cold (sub-mK) temperatures required for a variety of studies, which include both spectroscopy and the probing of the gravitational interaction of the anti-atom. We show that both cross section and rate are increased with the use of a resonant laser field.</p><p>

<p> The Langmuir-Blodgett deposition process is investigated for creating polystyrene nanosphere monolayers on a hydrophilic silicon substrate. The monolayers are fabricated over areas ~1 cm² and sputter coated with 100&Aring; of permalloy. The quality of the monolayers is analyzed with optical microscope image processing, and 2D Fourier transforms of electron microscope images. The magnetic switching behavior of the sputtered samples is measured using an alternating gradient magnetometer, and compared to completely flat permalloy. The magnetic hysteresis measurements are done at different angle between the easy and hard axis of the flat permalloy films. The measurements show different hysteresis shapes for nanosphere patterned permalloy and flat permalloy, with the difference becoming greater nearer the hard axis of the flat permalloy samples. The ambiguity of an easy or hard axis on a curved surface is likely to contribute to the difference in magnetic switching behavior between the two sample types.</p><p>

<p> Thin films of chlorine (Cl) and copper (Cu) doped zinc selenide (Cl:ZnSe and Cu:ZnSe) were fabricated by pulsed laser deposition (PLD) with the goal of enabling a multilayered semiconductor structure for a mid-infrared (mid-IR) electrically excited laser. Doping of ZnSe is achieved by varying the mass ratio of zinc chloride (ZnCl₂) or copper selenide (Cu₂Se) to ZnSe precursors in starting pressed powder targets. Appropriate adjustment of the fraction of dopant precursor in the mixtures allows for the control of the dopant concentration, N<i>_D</i>&ndash;N<i>_A</i> for N<i>_D</i> >> N<i>_A</i> (or N<i>_A</i>-N<i>_D</i> for N<i>_A</i> >> N<i>_D</i>) in the thin films, where N<i>_D</i> is the donor concentration and N<i>_A</i> is the acceptor concentration. PLD is used to ablate the Cl:ZnSe or Cu:ZnSe targets, to produce thin films on gallium arsenide (GaAs) substrates. Impedance spectroscopy allows current-voltage and capacitance-voltage (C-V) characterization. Specifically Mott-Schottky measurements determine N<i>_D</i>-N<i>_A</i> (or N<i>_A</i>-N<i>_D</i>) of the fabricated thin film samples with comparisons to the nominal dopant concentration of the targets. The Mott-Schottky, 1/C² vs. V, measurements for determining N<i>_D</i>-N<i>_A</i> were calibrated against well-characterized silicon wafers with known values of N<i>_D</i>. The goal of this project was to demonstrate a reliable method for controlling the dopant concentration in PLD-deposited Cl:ZnSe and Cu:ZnSe thin films. The results obtained allows for the fabrication of Cl:ZnSe and Cu:ZnSe thin films with known N<i>_D</i>-N<i>_A</i> for use in a mid-IR electrically-excited laser devices under development in our research group.</p><p>

<p> We have investigated the Faraday effect of bismuth-doped rare-earth iron-garnets with varying doping levels of gallium from z = 1.0 to 1.35. We used lutetium to control the film's in-plane magnetic properties and found that gallium doping levels above the compensation point caused a loss of anisotropy control, a canted out-of-plane magnetization in the film, and an extremely weak but linear coercivity above 10 micro-Tesla fields. Using these results we focused on in-plane films to create 8 layer stacks of 500 um thick films to achieve a minimum detectable field of 50 pT at 1 kHz. Unlike previous Magneto-Optic (MO) studies that typically used thin films of approximately 1um thickness, we used approximately 400um thick films to allow experimentation with the final, robust, ideal form the MO sensor would take. We measured what most other MO studies with garnets neglected: the magnetic anisotropy axis or structure within the film. Knowledge of this structure is essential in improving the sensitivity of a stacked MO probe. Studying thick films proved to be key to understanding the magnetic anisotropy and domain properties that can degrade or enhance the sensitivity of the Faraday rotation in bismuth doped rare-earth iron-garnets to an applied magnetic field and to pointing the direction of future research to develop the conditions for rugged magnetometer sensors. </p><p>

In this thesis, an investigation into the modal characteristics of novel beam shapes is presented. Sculpting the phase profile of a Gaussian beam can result in the generation of a beam with unique properties. Described in this thesis are Laguerre-Gaussian (LG), Hermite-Gaussian (HG) and Bessel beams (BBs). The diffraction of LG beam modes from a triangular aperture is explored and this effect can be used for the efficient measurement of the azimuthal mode index l that indicates the number of multiples of 2π of phase changes that the field displays around one circumference of the optical axis. In this study, only LG beams with zero radial mode index p, with p + 1 denoting the number of bright high intensity concentric rings around the optical axis, were considered. Then, a powerful approach to simultaneously determine both mode indices of a pure LG beam using the principal component analysis (PCA) algorithm on the observed far-field diffraction patterns was demonstrated. Owing to PCA algorithm, the shape of the diffracting element used to measure the mode indices is in fact of little importance and the crucial step is ‘training' any diffracting optical system and transforming the observed far-field diffraction patterns into the uncorrelated variables (principal components). Our PCA method is generic and it was extended to other families of light fields such as HG, Bessel and superposed beams. This reinforces the widespread applicability of this method for various applications. Finally, both theoretically and experimentally investigations using interferometry show the definitive linkage between both the radial and azimuthal mode indices of a partially coherent LG beam and the dislocation rings in the far-field cross-correlation function (CCF).