A detailed experimental study has been made of the surface topography of sixty cubic diamonds from the Congo, by means of optical microscopy, electron microscopy, scanning electron microscopy and cathodoluminescence. Ultra violet absorption studies indicate that all sixty cubic crystals are type I.A comprehensive review is given, of the general properties of diamond, its crystal growth, and previous work on the topography of cube faces. A detailed description of the general characteristics of tetragons is given, and a classification of tetragons according to their type, as point bottomed and flat bottomed, is given for the first time. The mechanism of the formation of tetragons is also discussed in chapter VIII. The arrangement of some small tetragons over a considerable area in the form of rows running parallel to the 100 direction has also been studied. It is suggested that such arrangements of pits are produced along grain boundaries on the surface of the crystal by dissolution in nature. The roughness of the cubic surfaces of natural diamond is largely attributed to the frequent appearance of tetragons, which are very deep and sometimes have complex structures, in addition to the existence of different facets of (111) and (110) on the surface. Of the sixty cubic crystals examined, eight showed different crystallographic facets on their surfaces, in addition to the cubic faces, such as octahedral facets, characterized by trigons. These are observed in different areas on the surface, juxtaposed on the cubic faces with tetragons. Some of the octahedral facets are oriented in opposite directions and show adjacent trigons which sometimes appear as parallelogram shaped features. Another striking feature is the appearance of trigons on the octahedral facet of the side wall of some tetragons. This phenomenon supports the theory that the cubic crystal grows by layers on the (111) planes. The occurrence of trigons also at the truncated. octahedral corners of some cubic crystals has been studied. The presence of many octahedral facets, either at the corners of some crystals or at different places on the surface, suggests that this type of cubic crystal grew by layer deposition on the (111) planes. The square shaped pits produced by laboratory etching in KNO on the natural and polished surfaces of cubic diamond have also been studied. It is found that the etch pits are distributed at random or they are crowded together on some areas on the surface, which are the sites of dislocations. Aspects of the internal structure of diamond, as revealed by etching cut surfaces were also studied. The etch patterns showed areas of heavy and light etching which accord with the pattern obtained by X-ray topography and are explained as a combination of the normal facets and the non-faceted hummocky surfaces whose mean orientation was roughly 100.

Thin evaporated films have been used to study the effects on reflection and transmission of visible and near visible light through solids by modulating the temperature of the specimen and the electric field in which it is situated. The principal aims of the studies were;(a) to obtain reliable data for comparison with electronic band structure calculations(b) to investigate a possible device application. Thermally modulated reflectance measurements have been performed on thick absorbing films of gold and copper and on the heavy rare earth metals, gadolinium, terbium, dysprosium and erbium. The modulated reflectance results have been transformed to Deltae2, the change in the imaginary part of the dielectric constant, by the Kramers-Kronig method of analysis. The Ae2 spectra have been correlated with electronic band structure calculations. Shifts in the principal absorption edges of gold and copper with temperature (shifts of - 2.3 x 10 4 eV/k and - 1.2 x 10 4 eV/K respectively), not - previously observed in thermal modulation experiments although theoretically predicted by expanded lattice band structure calculations, have been detected, The technique has been found to be capable of locating weak structure in the Deltae2 dispersion curve. New thermal modulation experiments on the heavy rare earth metals have enabled changes in the DeltaRp/Rp spectra to be observed as the temperature of the sample is decreased. These changes occur at the magnetic ordering temperatures and have not previously been observed using conventional static reflectance. By using electro-modulation, an integrated thin film optical modulator has been produced. The device has been constructed from thermally evaporated thin films of aluminium, silicon monoxide and cadmium sulphide, the latter being the active medium. Modulation degrees of between 10 and 15% have been observed for very low modulating voltages ~ 15 volts. However the device is limited by the very large insertion loss at the centre of the cadmium sulphide absorption edge. Some studies have been made on the electro-modulation of metals using a "dry-package" configuration. No electro-modulation response of the metal was observed. This null result is in contradiction to electrolytic measurements. Computational analysis has been performed to demonstrate that the electroreflectance spectra observed using the electrolytic technique may not be an electro-modulation of the optical constants of the metal but an absorption induced by the modulating electric field in the Gouy region of the electrolyte.

A number of interaction mechanisms of laser light with matter are reviewed; these include laser induced damage, nonlinear optics and various types of scattering. A comprehensive experimental study of laser induced damage is described. This damage is caused to a glass surface bearing a thin gold film while being illuminated by an argon ion laser beam. Small diffraction gratings can be produced by placing thin metallic films inside a ruby laser cavity. In such an arrangement the intense light of the laser is obliquely incident on the thin partially absorbing film simultaneously from two opposite directions, heating occurs, therefore, much more rapidly at the antinodes than at the nodes of the resulting standing wave. This heating can cause evaporation and ionization of the film. Since the film intersects the antinodes of the standing wave in a series of lines, this removal of the film material results in the creation of a diffraction grating. A time resolved investigation has been made of the development of such gratings in a number of metallic films, and the effect of film thickness, incident laser intensity, and angular orientation of the film has been studied. A solution of the time dependent stimulated scattering equations is obtained. Using a new approach it is shown that by suitable convolutions, the time dependent stimulated scattering gain profile for absorbing and nonabsorbing liquids can be directly obtained from the steady state scattering results. Laser mode locking techniques are detailed and a description is given of a ruby ring laser system. This system was able to deliver pulses as short as 25 picoseconds in duration and with peak intensities of 100 MW/cm2.

The proposed ion optics extraction geometry from ARIEL has been optimized based on simulations with Comsol. Geometrical parameters such as the acceleration gap and angle of the face of the vacuum chamber were studied in order to improve the beam 4-emittance and beam spot size. For geometries of interest, additional studies have been performed: voltage dependence, mass dependence, and the effect of the ion source misalignment on the beam parameters and how to compensate them. Simulations and experimental measurements were also performed for the current ISAC surface ion source to corroborate the simulation results. / Graduate / famaldo@uvic.ca

Because of the calculational speed of the fast Fourier transform (FFT) calculational algorithm for computing the discrete Fourier transform (DFT) and the usually small number of discrete components necessary to represent the data and its restoration, discrete Fourier techniques have been found to be the most efficient for data enhancement and restoration operations. / The thrust of this research has been the development of fast and efficient procedures for determining the continued Fourier spectrum, or the continued interferogram for FTS data, with the application of as many of the pertinent physical constraints as possible. The inverse DFT is a Fourier series, and the coefficients of the sinusoids are the discrete spectral components. This Fourier series is added to the function formed from the low frequency band, (or to the interferogram for FTS data) and the sum of the squared error is minimized in the total function to produce a set of linear equations in these high frequency coefficients for the constraint of finite extent, and a set of nonlinear equations for the constraint of minimum negativity. A variation of the method of successive substitutions was adapted that is very efficient in solving the set of nonlinear equations. The procedure to implement the constraint of minimum negativity has been found to easily accommodate the constraints of finite extent and the minimization of values above an upper bound also, so that all these constraints may be simultaneously applied to a given set of data. Further, the procedure to implement the constraint of minimum negativity has proven very insensitive to noise error. / The above procedures for implementing the constraints of finite extent and minimum negativity have proven successful in the restoration of both simulated and experimental infrared spectroscopy data. For infrared grating spectroscopy data the data are first inverse filtered, then the constraints are applied to continue the Fourier spectrum. For FTS data, it is the interferogram that is continued. In certain cases the interferogram is pre-multiplied by a suitable window function before extension in order to reduce the artifacts. / Source: Dissertation Abstracts International, Volume: 43-03, Section: B, page: 0771. / Thesis (Ph.D.)--The Florida State University, 1982.

A spectral broadening of 1.3 $\pm$ 0.2 MHz was observed in laser light forward scattered through a solution of water and particulates. Laser light from a single mode argon-ion laser was collected after scattering through water with the addition of particulate matter. The collected light was analyzed with a diffraction grating, a Fabry-Perot spectrometer and a light mixing technique. The grating spectrometer measures spectra in the gigahertz range, the Fabry-Perot in the megahertz, and the mixing technique measures in the kilohertz range. The only non-null results were found with the Fabry-Perot spectrometer. Broadening was only observed when the added particles were smaller than the wavelength of the illuminating laser. The broadening is attributed to coupling between fluctuations in particle concentration and fluctuations in entropy. Entropy fluctuations exist in a pure fluid, although they are very weak in water. The presence of the particles induces entropy fluctuations (or temperature gradients) in the fluid which, in turn, induce fluctuations in particle concentration. / It was found that the best fit to the scattered spectra was a Voigt with a large Gaussian component. The coherence theory was extended to a multimode source. The fringe visibility versus path difference in a Michelson interferometer was calculated for single and multimode Gaussian and Lorentzian spectra. Data were taken with a multimode argon-ion laser coupled with a Michelson interferometer and compared to the theoretical calculation. The fringe visibility for the scattered, multimode laser matches the Gaussian multimode calculation. This may be a useful result for enhancing the capability of remote sensors. / Source: Dissertation Abstracts International, Volume: 56-08, Section: B, page: 4396. / Major Professor: David VanWinkle. / Thesis (Ph.D.)--The Florida State University, 1995.

<p> With the development of ultra-fast laser technology, several new imaging techniques have pushed optical resolution past the diffraction limit for traditional light-based optics. Advancements in lithography have enabled the straightforward creation of micron- and nanometer-sized optical devices. Exposing metal-dielectric structures to light can result in surface plasmon excitation and propagation along the transition interface, creating a surface plasmon polariton (SPP) response. Varying the materials or geometry of the structures, the plasmonic response can be tailored for a wide range of applications. </p><p> Photoemission electron microscopy (PEEM) has been used to image excitations in micron-sized plasmonic devices. With PEEM, optical responses can be characterized in detail, aiding in the development of new types of plasmonic structures and their applications. We show here that in thin, triangular gold platelets SPPs can be excited and concentrated within specific regions of the material (thickness ~50 nm); resulting in localized photoemission in areas of high electric field intensity. In this regard, the platelets behave as receiver antennas by converting the incident light into localized excitations in specific regions of the gold platelets. The excited areas can be significantly smaller than the wavelength of the incident light (&lambda; &le; 1 &micro;m). By varying the wavelength of the light, the brightness of the excited spots can be changed and by varying the polarization of the light, the brightness and position can be changed, effectively switching the photoemission on or off for a specific region within the triangular gold structure. </p><p> In this work, the spatial distribution of surface plasmons and the imaging results from photoemission electron microscopy are reproduced in simulation using finite element analysis (FEA). In addition, we show that electromagnetic theory and simulation enable a detailed and quantitative analysis of the excited SPP modes, an explanation of the overall optical responses seen in PEEM images, and prediction of new results.</p><p>

<p> Laser absorption spectroscopy is a non-intrusive diagnostic tool particularly well-suited to investigate the dynamic and harsh conditions commonly found within combustion systems. By measuring the amount of light absorbed at specific wavelengths that are resonant with rotational-vibrational transitions in molecules, absorption spectroscopy gives a measure of the molecular population in particular quantum states. Experimental spectra are fit with a simulation generated from spectral line shape models combined with a spectroscopic database to infer species concentrations, temperature, and pressure. Dual frequency comb spectroscopy (DCS) with mode-locked frequency comb lasers is an emerging form of absorption spectroscopy that yields both high resolution (&lt; 1 GHz) and broad bandwidth spectra (> 10 THz) on rapid timescales (&lt; 2 ms). There are two key challenges facing DCS in dynamic combustion environments. First, obtaining high signal-to-noise-ratio (SNR) spectra has traditionally involved coherently averaging hundreds of individual spectra over seconds to minutes before fitting. Second, at the high temperatures and pressures commonly found within combustion systems, the existing line shape models and spectroscopic databases are known to not capture all of the key molecular physics, thereby requiring empirical extension and validation. This work presents techniques to enable rapid DCS measurements of thermodynamic properties in dynamic high-pressure, high-temperature, environments through power optimization and apodization to improve the short-term SNR. A rapid compression machine at Colorado State University is instrumented with a portable DCS spectrometer and temperature is recovered at 704 &micro;s resolution from 1&ndash;21 bar and 294&ndash;566 K. This demonstrates the ability of DCS to be applied to combustion-relevant timescales for both broad bandwidth and high resolution non-intrusive measurements of harsh systems. The design development of an optical testbed that creates a well-known, high-temperature, and high-pressure environment is additionally discussed. This subsequently will enable determination of the accuracy limitations of existing molecular absorption models, as well as allow for model expansion. Together these abilities enable laser measurements to better evaluate and optimize combustion systems, including improved understanding of the underlying molecular processes. Proper understanding of the molecular dynamics will allow for instrumentation and quantification of more extreme environments such as inside rocket engines or the atmospheres of distant planets. </p><p>

Previous work on efficiency of light injection into the core of a fiber from a thin film and a bulk distribution of sources in the cladding, have made use of the fields of a weakly guiding fiber. This approximation simplifies the analysis of the power efficiency by introducing universal values for the eigenvalues of different fibers with same {dollar}V{dollar}-number, but can not predict accurately the behavior of the injected light into a fiber with arbitrary differences in indices of refraction. We have used the exact field solution in the expressions of the power efficiency, {dollar}P\sb{lcub}\rm eff{rcub}{dollar}, and analyzed its behavior as a function of the remaining parameters. Although more complicated and harder to interpret, our formulas allow us to analyze the power injection efficiency of fibers with arbitrary differences in the indices of refraction. The results obtained are relevant for the design of more efficient optical fiber distributed sensors. The conclusions follow.;We have confirmed weakly guiding results obtained previously. However, we have found that the {dollar}P\sb{lcub}\rm eff{rcub}{dollar} does not always increase with the {dollar}V{dollar}-number but with the difference in the indices of refraction, {dollar}n\sb{lcub}\rm core{rcub} -n\sb{lcub}\rm clad{rcub}{dollar}.;For fixed {dollar}a/\lambda{dollar}, indices of refraction, {dollar}n\sb{lcub}\rm core{rcub}{dollar} and {dollar}n\sb{lcub}\rm clad{rcub}{dollar} and normalized inner and outer radius, {dollar}R\sb{lcub}\rm in{rcub}{dollar} and {dollar}R\sb{lcub}\rm out{rcub}{dollar}, the {dollar}P\sb{lcub}\rm eff{rcub}{dollar} is independent of core radius, {dollar}a{dollar}, and the wavelength, {dollar}\lambda{dollar}. This applies for any uniform cylindrical distribution of cladding sources. This result suggests that {dollar}a/\lambda, R\sb{lcub}\rm in{rcub}{dollar} and {dollar}R\sb{lcub}\rm out{rcub}{dollar} are independent variables.;For the bulk distribution we have found that {dollar}P\sb{lcub}\rm eff{rcub}{dollar} increases with the wavelength, {dollar}\lambda{dollar}, and decreases with the fiber core radius, {dollar}a{dollar}, i.e., it decreases with the {dollar}V{dollar}-number. However, for the thin film, the {dollar}P\sb{lcub}\rm eff{rcub}{dollar} remains almost constant with the wavelength, {dollar}\lambda{dollar}, and fiber core radius, {dollar}a{dollar}.

archives@tulane.edu / This dissertation details a measurement of the n-$^{4}$He coherent scattering length to be $b_{4\rm{He}} = [3.0982 \pm\: 0.00214\; (\rm{stat}) \pm\: 0.00077\; (\rm{sys})]$ fm utilizing a perfect silicon crystal neutron interferometer. This measurement provides over a factor of 10 improvement in precision and differs by $0.162$ fm compared to the most commonly used value. Neutron interferometry provides a tool for precision scattering lengths measurements for a variety of isotopes. Examples include coherent scattering length measurements for $^{1}$H, $^{2}$H, $^{3}$He and the incoherent scattering length of $^{3}$He. Neutron scattering lengths of light nuclei provide useful tests of nuclear potential models and serve as inputs for nuclear effective field theories. A monolithic, perfect silicon neutron interferometer splits the wave function of a single neutron via Bragg diffraction into two coherent paths spatially separated to the extent of a few centimeters. A sample of $^{4}$He gas, contained within an aluminum cell, is introduced into one beam path which produces a phase shift directly proportional to $b_{4\rm{He}}$. Significant effort has been spent quantifying important systematic considerations that include thermal transfer from the gas cell to the interferometer crystal and deformation of the gas cell walls due to gas pressure which ranges from 7 bar to 13 bar which were calculated by an FEA simulation. Thermal transfer between the gas cell and interferometer crystal induces a change of the intrinsic interferometer phase which is dependent on sample position. This additional systematic phase has been named the shadow phase. A glycol cooling system was used to mitigate the shadow phase and a special measurement pattern was devised to account for possible shadow phase drift. This work was performed at the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR). / 1 / Robert Haun