Optimization of dichromated gelatin (DCG) film coatings for holographic recording is presented. The Taguchi optimization method is applied to DCG film coatings to obtain high uniformity. Two-level factorial design is used to optimize the emulsion curing conditions for high diffraction efficiency. Film thicknesses ranging from 6.0 to 23.4 mum are obtained with uniformities between 4.0 and 8.0%. Peak diffraction efficiencies between 87.0 and 96.9% are obtained using the optimized curing conditions. A possible holographic formation mechanism is introduced and experimental results for shrinkage and swelling are summarized. Both reflection type substrate mode holograms and polarization selective transmission type holograms are fabricated using optimized films. An improved Brewster angle method is also used to obtain an accurate measurement of the refractive index of DCG films, which are important in the design of holographic optical elements.

Metal contamination levels are a growing concern in integrated circuit manufacturing because they degrade electrical performance. This work uses statistical design of experiments to determine deposition characteristics of transition and heavy metal contaminants onto silicon surfaces from process chemicals that are used in wafer cleaning. Copper, gold, molybdenum, silver, lead, chromium, tin, titanium, manganese, and tungsten were added to buffered oxide etchant (BOE or BHF) and hydrofluoric acid (HF) solutions. Wafers were immersed in these solutions and evaluated by total reflection x-ray fluoresence (TXRF) surface analysis. For those metals that are found to deposit from solution, statistical analysis is utilized to develop empirical models which describe the deposition characteristics.

A newly designed Langmuir probe has been evaluated and was used to map the plasma potential near the powered electrode of a plasma etch chamber in 2 dimensions. Various electrode materials and geometries were used in order to investigate the relationship between electrode design and the presence of localized regions of elevated plasma potential. These regions of elevated plasma potential were known to be responsible for the presence of particle clouds suspended in the plasma during operation. A relationship was established between sharp edges on the powered electrode, insulating materials on the electrode and localized elevation in plasma potential. A thin layer of raised plasma potential has also been discovered at the plasma-sheath boundary. Suggestions for electrode design to reduce the presence of particles suspended in the plasma are made.

With the increasing demand for high storage density, magnetic recording media will soon have as their basic components single-domain ferromagnetic grains. Recently experimentalists working with powerful new microscopic techniques have discovered that the process of magnetization reversal in these grains is much more complicated than had been previously realized. In this dissertation we investigate the applicability of the two-dimensional kinetic Ising model on a square lattice as a model for the switching dynamics. The process of metastable decay is studied by two means: Monte Carlo simulations and analytical arguments based on droplet theory. The simulations are shown to be consistent with the analytical arguments and qualitatively similar to the experimental measurements of single-domain ferromagnets. / For a periodic Ising system with an initial magnetization $m\sb0$ = +1 in a negative magnetic field, the field $H\sb{\rm sw}$ which causes the magnetization to decay to zero in a specified length of time is found as a function of the system size L. The probability that the magnetization remains greater than zero is also found as a function of time for fixed applied field and as a function of applied field for fixed decay time. / The magnetostatic dipole-dipole interaction in real magnetic materials is modeled to lowest order by adding to the Ising Hamiltonian a term proportional to the square of the magnetization. The analytical predictions show excellent agreement with Monte Carlo simulations with no fitted parameters that depend on the $m\sp2$ term. / Finally, $H\sb{\rm sw}$ is found from Monte Carlo simulations of octagonal systems with a variety of boundary conditions. The results are explained in terms of the scaling form of the free-energy barrier which must be overcome for the metastable state to decay, and they demonstrate the importance that surface effects such as adsorption and reconstruction might have on magnetization switching. / Source: Dissertation Abstracts International, Volume: 57-04, Section: B, page: 2634. / Major Professor: Per Arne Rikvold. / Thesis (Ph.D.)--The Florida State University, 1996.

Magnetic Resonance Imaging allows electromagnetic properties of the brain to be measured in vivo, providing new markers of structure at a microscopic level. Evaluation of the local complex signal evolution observed using a multi-echo gradient-echo (MEGE) sequence can allow the electromagnetic and relaxivity properties of individual tissue compartments to be accessed. The phase evolution carries valuable information about the different compartments, but is dominated by non-local, large-length-scale field variations which present the main challenge in processing complex MEGE data. In this work 2-compartment and 3-pool models are used to describe signal evolution from a mixed tissue and venous compartment and from white matter, respectively. A new method for removing the effects of non-local field variations without corrupting local non-mono-exponential phase evolution is proposed. The 2-compartment model of venous blood complex signal has been used to access the vascular dependence on orientation and oxygenation levels, and has been validated against existing methods on large distinguishable veins. A phantom consisting of capillary tubes filled with ferritin solution immersed in a water bath has been used to validate the 2-compartment model and the estimated frequency offsets between the ferritin and water compartments at multiple orientations to B⃗0 shown to agree with predictions of theory. White matter in the corpus callosum has been investigated using a saturation-recovery MEGE sequence with variable flip angles with the aim of revealing differences in the T1-relaxation properties of the myelin, the external and the intra-axonal water compartments. The results show that the relative saturation of the myelin water compartment decreases with increasing flip angle and is consistent with there being a short-T1 component associated with myelin water. However, the observed signal behaviour shows less contrast than expected based on the findings from the previous studies. This could be related to differences in exchange rates between compartments. Finally, diffusion-weighted, asymmetric spin-echo imaging was used to simultaneously investigate the diffusivity and electromagnetic properties of the external and intra-axonal compartments of white matter. This approach could provide additional information about white matter microstructure. Asymmetry of the spin echo sequence was achieved by delaying the acquisition by ∆t. The preliminary results show an increase in the scaled magnitude with echo delay at a constant b-value in some regions of the corpus callosum. The preliminary results are promising, but further investigation and method development are required. This thesis has investigated a number of novel methods of studying white matter structure and cerebral microvasculature.

No description available.

Most existing terahertz imaging systems are generally limited by slow image acquisition due to mechanical raster scanning. Other systems using focal plane detector arrays can acquire images in real time, but are either too costly or limited by low sensitivity in the terahertz frequency range. To design faster and more cost-effective terahertz imaging systems, the first part of this thesis proposes two new terahertz imaging schemes based on compressive sensing (CS). Both schemes can acquire amplitude and phase-contrast images efficiently with a single-pixel detector, thanks to the powerful CS algorithms which enable the reconstruction of N-by- N pixel images with much fewer than N2 measurements. The first CS Fourier imaging approach successfully reconstructs a 64x64 image of an object with pixel size 1.4 mm using a randomly chosen subset of the 4096 pixels which defines the image in the Fourier plane. Only about 12% of the pixels are required for reassembling the image of a selected object, equivalent to a 2/3 reduction in acquisition time. The second approach is single-pixel CS imaging, which uses a series of random masks for acquisition. Besides speeding up acquisition with a reduced number of measurements, the single-pixel system can further cut down acquisition time by electrical or optical spatial modulation of random patterns. In order to switch between random patterns at high speed in the single-pixel imaging system, the second part of this thesis implements a multi-pixel electrical spatial modulator for terahertz beams using active terahertz metamaterials. The first generation of this device consists of a 4x4 pixel array, where each pixel is an array of sub-wavelength-sized split-ring resonator elements fabricated on a semiconductor substrate, and is independently controlled by applying an external voltage. The spatial modulator has a uniform modulation depth of around 40 percent across all pixels, and negligible crosstalk, at the resonant frequency. The second-generation spatial terahertz modulator, also based on metamaterials with a higher resolution (32x32), is under development. A FPGA-based circuit is designed to control the large number of modulator pixels. Once fully implemented, this second-generation device will enable fast terahertz imaging with both pulsed and continuous-wave terahertz sources.

Based on the plasmon hybridization theory, this thesis provides physical understanding of the plasmonic nature of metallic nanostructures. Metallic films and nanoshell particles exhibit bonding and antibonding plasmon resonances formed by hybridization of plasmon resonances associated with the two surfaces confining the metal. For both structures the lower energy bonding plasmon resonance is characterized by symmetric alignment of the charge densities. This thesis presents a physically intuitive explanation for why the repulsive symmetric charge alignment results in a low energy bonding plasmon. It also shows that the plasmon dispersion for a planar thin film can be obtained from the plasmon resonances of a metallic nanoshell in the limit of infinite radius. After clarifying the nature of plasmon modes of thin metal films, the optical properties of an individual nanohole in a thin metallic film are examined theoretically and experimentally. Subwavelength holes, one of the most important structures in nanophotonics, give rise to extraordinary transmission when patterened in arrays. The individual holes provided a site for excitation of the underlying thin film surface plasmons. It is shown that both hole diameter and film thickness determine the energy of the optical resonance. I also show that the hole plasmon resonance (HPR) depends strongly on the polarization of the incident light due to the optical coupling between antibonding film plasmon modes and perpendicularly polarized light to the film surface. The hybridization scheme is extended to the coherent coupling between the localized plasmons of a nanoshell and the excitons of J-aggregate molecules adsorbed on the metallic nanoparticle surface. Timing the nanoshell plasmon resonant energies across the exciton energy of the J-aggregate obtains hybridized energies for plasmon-exciton coupling. The coupling strength depends on the specific plasmon mode of the nanoshell coupled to the exciton mode of the J-aggregate. Experimental data of optical extinction spectra is reproduced by using Mie theory, and the plasmon-exciton coupling of nanoshell/J-aggregate complexes systems can be quantitatively as well as qualitatively understood based on Gans theory. The plasmon hybridization theory can be also applied to various shapes of nanopartides using particular coordinate systems. This thesis investigate the optical properties of metallic toroidal nanoparticles using the plasmon hybridization theory. For incident light polarized in the plane of the torus, a low energy dipolar plasmon resonance and a high energy resonance contributed by several higher order torus modes appear in the optical spectra. The low energy node is highly tunable with the aspect ratio in terms of two characteristic radii of tori. For perpendicular polarization, the plasmon resonance is weakly dependent on the aspect ratio because the excited higher order torus modes are closely spaced. Optical spectra calculated by plasmon hybridization method show excellent agreement with numerical finite difference time domain calculation results.

This thesis looks at three aspects of electron dynamics in single-walled carbon nanotubes (SWNTs): electron spin resonance (ESR), conductivity, and the dynamic Franz-Keldysh effect (DFKE). The temperature dependence of ESR in annealed SWNTs is presented. It is shown that the spin susceptibility is greatly increased due to the absence of oxygen. In addition, the electrons become more localized due to the annealing, leading to a change in the asymmetry of the ESR signal as a function of temperature. I observe motional narrowing of the ESR resonance. Temperature dependent conductivity of SWNT decant films is also presented. These measurements support the ESR data by indicating that electron movement is hindered as temperature is lowered. Last, this thesis describes the first attempt to observe DFKE in SWNTs. Using a free electron laser pump-white light probe and a fiber CCD detection scheme, I attempted to observe the DFKE in an DGU-enriched film.

In this thesis, we theoretically study the plasmonic properties of metallic nanostructures with reduced symmetry using the Plasmon Hybridization (PH) and the Finite Difference Time Domain (FDTD) methods. Both methods provide efficient and accurate results for calculating physical properties of metallic nanostructures, including the optical cross section spectra, the local electromagnetic fields and induced charge densities around the surface of the nanostructures. The PH method is applied to a nanoshell with an offset core (nanoegg). The results show that the reduction in symmetry relaxes the selection rules in the hybridization of primitive plasmon modes, allowing for an admixture of dipolar components in higher multipolar plasmon modes of the particle. The hybridization therefore makes higher multipolar nanoshell plasmon modes dipole active, resulting in a core offset-dependent shift for the plasmon energies and a multipeaked feature in the optical spectrum. The polarization dependence of the optical absorption spectra is found to be relatively weak. The calculations also show significantly larger local-field enhancements on nanoegg's external surface than the equivalent concentric spherical nanostructure. The results agree very well with results from FDTD simulations and experiments, suggesting applications of nanoeggs as substrates for surface enhanced Raman spectroscopy (SERS) Another comprehensive investigation of the plasmonic interactions of individual metallic nanoshells with dielectric substrates is performed using the FDTD method. The results show that the adjacent dielectric breaks the spherical symmetry of individual nanoshell and lifts the degeneracy of the dipole and quadrupole plasmon modes, introducing significant polarization dependent redshifts and hybridization of the nanoparticle plasmon resonances. The results also show that, for small nanoparticle-substrate separations and substrates with large dielectric permittivities, the hybridized quadrupolar nanoparticle plasmon resonances also appear in the scattering spectrum. We discuss different numerical approaches in FDTD simulations for calculating the scattering spectrum in typical dark-field scattering geometries. We also discuss issues of numerical convergence and show that the scattering spectra can be calculated using finite substrate slab models. The results agree very well with experiments, showing that dielectric substrates matter in optical measurements of plasmonic nanoparticles. FDTD method is also applied to a bowtie-shaped nanostructure (nanobowtie). The calculations show significantly large SERS enhancements across a broad bandwidth of exciting wavelengths because of the complicated mode structure possible in the interelectrode gap. Nanometer-scale asperities in the gap area break the inter-electrode symmetry of the structure, resulting in optical excitations of many inter-electrode modes besides the simple dipolar plasmon mode commonly considered. The broken symmetry also leads to much less dependence of the calculated enhancement on polarization direction, as seen experimentally. The calculations confirm that the electromagnetic enhancement is confined in the normal direction to the film thickness and to a region comparable to the radius of curvature of the asperity. The calculated electromagnetic enhancements can exceed 1011, approaching that sufficient for single-molecule sinsitivity. We also compare the calculated extinction spectra for various values of interelectrode conductance connecting the source and drain. The results show that negligible charge transfer occurs between the two electrodes until junction conductance approaches the conductance quantum, G 0 = 2e2/h.