Open Access. Powered by Scholars. Published by Universities.®

Physics Commons

Open Access. Powered by Scholars. Published by Universities.®

Articles 1 - 28 of 28

Full-Text Articles in Physics

Modeled And Observed N2 Lyman-Birge-Hopfield Band Emissions Earth's Dayglow: A Comparison, Donald Murray Jan 2007

Modeled And Observed N2 Lyman-Birge-Hopfield Band Emissions Earth's Dayglow: A Comparison, Donald Murray

Electronic Theses and Dissertations

Ultraviolet (UV) spectra obtained from Earth’s dayglow contain important information for understanding the thermosphere, and the N2 Lyman-Birge-Hopfield (LBH) bands are possibly the most useful emission. To be useful, a thorough understanding of how the LBH band emission varies with altitude and latitude is essential to present and future use of this emission by space-based remote sensors. Excited by photoelectron impact on N2 leading to transitions from the a 1Πg state to the ground state, the LBH emissions radiate between 1270 and 2400 Å. In addition to being populated by electron impact excitation, the a 1Πg state is populated ...


Optical And Physical Properties Of Ceramic Crystal Laser Materials, Jed Simmons Jan 2007

Optical And Physical Properties Of Ceramic Crystal Laser Materials, Jed Simmons

Electronic Theses and Dissertations

Historically ceramic crystal laser material has had disadvantages compared to single crystal laser material. However, progress has been made in the last decade and a half to overcome the disadvantages associated with ceramic crystal. Today, because of the promise of ceramic crystal as a high power laser material, investigation into its properties, both physical and optical, is warranted and important. Thermal expansion was measured in this thesis for Nd:YAG (yttrium aluminum garnet) ceramic crystal using an interferometric method. The interferometer employed a spatially filtered HeNe at 633 nm wavelength. Thermal expansion coefficients measured for the ceramic crystal samples were ...


Raman Spectroscopic Study Of Single Red Blood Cells Infected By The Malaria Parasite Plasmodium Falciparum, William Carter Jan 2007

Raman Spectroscopic Study Of Single Red Blood Cells Infected By The Malaria Parasite Plasmodium Falciparum, William Carter

Electronic Theses and Dissertations

Raman micro-spectroscopy provides a non-destructive probe with potential applications as a diagnostic tool for cellular disorders. This study presents micro-Raman spectra of live erythrocytes infected with a malaria parasite and investigates the potential of this probe to monitor molecular changes which occur during differentiation of the parasite inside the cell. At an excitation wavelength of 633 nm the spectral bands are dominated by hemoglobin vibrations yielding information the on structure and spin state of the heme moiety. It also demonstrates the novel use of silica capillaries as a viable method for studying the erythrocytes in an environment that is much ...


Electrical Capacitance Volume Tomography Of High Contrast Dielectrics Using A Cuboid Geometry, Mark Nurge Jan 2007

Electrical Capacitance Volume Tomography Of High Contrast Dielectrics Using A Cuboid Geometry, Mark Nurge

Electronic Theses and Dissertations

An Electrical Capacitance Volume Tomography system has been created for use with a new image reconstruction algorithm capable of imaging high contrast dielectric distributions. The electrode geometry consists of two 4 x 4 parallel planes of copper conductors connected through custom built switch electronics to a commercially available capacitance to digital converter. Typical electrical capacitance tomography (ECT) systems rely solely on mutual capacitance readings to reconstruct images of dielectric distributions. This dissertation presents a method of reconstructing images of high contrast dielectric materials using only the self capacitance measurements. By constraining the unknown dielectric material to one of two values ...


Infrared Antenna-Coupled Phased-Array, Christopher Middlebrook Jan 2007

Infrared Antenna-Coupled Phased-Array, Christopher Middlebrook

Electronic Theses and Dissertations

Phased-array antennas are commonplace in the radiofrequency portion of the electromagnetic spectrum. Exploitation of phasing effects between multiple antennas facilitates a wide range of applications, including synthetic-aperture radar, beam forming, and beam scanning. For the first time, the phased addition of multiple dipole antennas is demonstrated in the infrared, at a wavelength of 10.6 micrometers. Coplanar strip lines are used to interconnect the antennas, preserving the phase of the individual contributions. Several different proof-of-concept experiments are performed, using planar antennas fabricated with direct-write electron-beam lithography. Infrared-frequency currents from two dipole antennas are summed together at a common feedpoint and ...


Rigorous Analysis Of Wave Guiding And Diffractive Integrated Optical Structures, Andrew Greenwell Jan 2007

Rigorous Analysis Of Wave Guiding And Diffractive Integrated Optical Structures, Andrew Greenwell

Electronic Theses and Dissertations

The realization of wavelength scale and sub-wavelength scale fabrication of integrated optical devices has led to a concurrent need for computational design tools that can accurately model electromagnetic phenomena on these length scales. This dissertation describes the physical, analytical, numerical, and software developments utilized for practical implementation of two particular frequency domain design tools: the modal method for multilayer waveguides and one-dimensional lamellar gratings and the Rigorous Coupled Wave Analysis (RCWA) for 1D, 2D, and 3D periodic optical structures and integrated optical devices. These design tools, including some novel numerical and programming extensions developed during the course of this work ...


High-Speed Modelocked Semiconductor Lasers And Applications In Coherent Photonic Systems, Wangkuen Lee Jan 2007

High-Speed Modelocked Semiconductor Lasers And Applications In Coherent Photonic Systems, Wangkuen Lee

Electronic Theses and Dissertations

1.55-µm high-speed modelocked semiconductor lasers are theoretically and experimentally studied for various coherent photonic system applications. The modelocked semiconductor lasers (MSLs) are designed with high-speed (>5 GHz) external cavity configurations utilizing monolithic two-section curved semiconductor optical amplifiers. By exploiting the saturable absorber section of the monolithic device, passive or hybrid mode-locking techniques are used to generate short optical pulses with broadband optical frequency combs. Laser frequency stability is improved by applying the Pound-Drever-Hall (PDH) frequency stabilization technique to the MSLs. The improved laser performance after the frequency stabilization (a frequency drifting of less than 350 MHz), is extensively studied ...


Micro-Optic-Spectral-Spatial-Elements (Mosse), Alok Ajay Mehta Jan 2007

Micro-Optic-Spectral-Spatial-Elements (Mosse), Alok Ajay Mehta

Electronic Theses and Dissertations

Over a wide range of applications, optical systems have utilized conventional optics in order to provide the ability to engineer the properties of incident infra-red fields in terms of the transmitted field spectral, spatial, amplitude, phase, and polarization characteristics. These micro/nano-optical elements that provide specific optical functionality can be categorized into subcategories of refractive, diffractive, multi-layer thin film dichroics, 3-D photonic crystals, and polarization gratings. The feasibility of fabrication, functionality, and level of integration which these elements can be used in an optical system differentiate which elements are more compatible with certain systems than others. With enabling technologies emerging ...


A Novel Setup For High-Pressure Raman Spectroscopy Under A Microscope, Thomas Andrew Oakeson Jan 2007

A Novel Setup For High-Pressure Raman Spectroscopy Under A Microscope, Thomas Andrew Oakeson

Electronic Theses and Dissertations

Functional properties of biological molecules and cells are affected by environmental parameters such as temperature and pressure. While Raman spectroscopy provides an intrinsic probe of molecular structural changes, the incorporation of a microscope enables studies of minuscule amounts of biological compounds with spatial resolution on a micron scale. We have developed a novel setup which combines a Raman microscope and a high pressure cell. A micro-capillary made out of fused silica simultaneously serves as the supporting body and the optical window of the pressure cell. The cell has been tested over the pressure range from 0.1 to 4 kbar ...


High Birefringence Liquid Crystals For Optical Communications, Amanda Jane Parish Jan 2007

High Birefringence Liquid Crystals For Optical Communications, Amanda Jane Parish

Electronic Theses and Dissertations

High birefringence (Δn>0.4) nematic liquid crystals are particularly attractive for infrared applications because they enable a thinner cell gap to be used for achieving fast response time and improved diffraction efficiency. In this thesis, the mesomorphic and electro‐optic properties of several new fluorinated isothiocyanate (NCS) terphenyl and phenyl tolane single compounds and mixtures are reported. The single compounds demonstrated Δn~0.35‐0.52 in the visible spectral region at room temperature and exhibit relatively low viscosity. It was found that lateral fluorine substitutions and short alkyl chains eliminate smectic phase and lower the melting temperature of ...


Far-Infrared/Millimeter Wave Source And Component Development For Imaging And Spectroscopy, Todd Du Bosq Jan 2007

Far-Infrared/Millimeter Wave Source And Component Development For Imaging And Spectroscopy, Todd Du Bosq

Electronic Theses and Dissertations

The far-infrared and millimeter wave (FIR/mmW) (wavelength 75 micrometer to 10 mm) portion of the electromagnetic spectrum is fairly underdeveloped technologically, owing to the large amount of atmospheric attenuation in that range. At present, the FIR/mmW region is lacking in compact, high-brightness radiation sources and practical imaging systems. This dissertation focuses on development of two complementary technologies in this area - an active mmW imaging system and high-reflectivity Bragg mirrors for the FIR p-Ge laser. The imaging system uses a vector network analyzer in the frequency range of 90-140 GHz as the radiation source and receiver. Raster scanning is ...


Spectroscopic Studies Of Laser Plasmas For Euv Sources, Simi A. George Jan 2007

Spectroscopic Studies Of Laser Plasmas For Euv Sources, Simi A. George

Electronic Theses and Dissertations

With the availability of high reflectivity multilayer mirrors and zone plate lenses, the EUV region (5nm - 40nm) of the electromagnetic spectrum is currently being explored for applications of nanoscale printing and imaging. Advances made in this area have consequences for many areas of science. Research for producing a compact, bright EUV source for laboratory use has gained momentum in recent years. For this study, EUV radiation is produced by irradiating target materials using a focused laser beam. Focused laser beam ionizes the target to create a hot, dense, pulsed plasma source, where emission is a result of the relaxation of ...


Hybrid Photonic Signal Processing, Farzan Naseer Ghauri Jan 2007

Hybrid Photonic Signal Processing, Farzan Naseer Ghauri

Electronic Theses and Dissertations

This thesis proposes research of novel hybrid photonic signal processing systems in the areas of optical communications, test and measurement, RF signal processing and extreme environment optical sensors. It will be shown that use of innovative hybrid techniques allows design of photonic signal processing systems with superior performance parameters and enhanced capabilities. These applications can be divided into domains of analog-digital hybrid signal processing applications and free-space--fiber-coupled hybrid optical sensors. The analog-digital hybrid signal processing applications include a high-performance analog-digital hybrid MEMS variable optical attenuator that can simultaneously provide high dynamic range as well as high resolution attenuation controls; an ...


Two-Dimensional Guided Mode Resonant Structures For Spectral Filtering Applications, Sakoolkan Boonruang Jan 2007

Two-Dimensional Guided Mode Resonant Structures For Spectral Filtering Applications, Sakoolkan Boonruang

Electronic Theses and Dissertations

Guided mode resonant (GMR) structures are optical devices that consist of a planar waveguide with a periodic structure either imbedded in or on the surface of the structure. The resonance anomaly in GMR structures has many applications as dielectric mirrors, tunable devices, sensors,and narrow spectral band reflection filters. A desirable response from a resonant grating filter normally includes a nearly 100% narrowband resonant spectral reflection (transmission), and a broad angular acceptance at either normal incidence or an oblique angle of incidence. This dissertation is a detailed study of the unique nature of the resonance anomaly in GMR structures with ...


Scanning Fabry-Perot Spectrometer For Terahertz And Gigahertz Spectroscopy Using Dielectric Bragg Mirrors, Justin Cleary Jan 2007

Scanning Fabry-Perot Spectrometer For Terahertz And Gigahertz Spectroscopy Using Dielectric Bragg Mirrors, Justin Cleary

Electronic Theses and Dissertations

A scanning Fabry-Perot transmission filter composed of a pair of dielectric mirrors has been demonstrated at millimeter and sub-millimeter wavelengths. The mirrors are formed by alternating quarter-wave optical thicknesses of silicon and air in the usual Bragg configuration. Detailed theoretical considerations are presented for determining the optimum design including factors that affect achievable finesse. Fundamental loss by lattice and free carrier absorption are considered. High resistivity in the silicon layers was found important for achieving high transmittance and finesse, especially at the longer wavelengths. Also considered are technological factors such as surface roughness, bowing, and misalignment for various proposed manufacturing ...


Scalable Volumetric Three-Dimensional Up-Conversion Display Medium, Jung-Hyun Cho Jan 2007

Scalable Volumetric Three-Dimensional Up-Conversion Display Medium, Jung-Hyun Cho

Electronic Theses and Dissertations

There are many different techniques to display 3D information. However, not many of them are able to provide sufficient depth cues to the observers to sense or feel the images as real three-dimensional objects. Volumetric three-dimensional displays generate images within a real 3D space, so they provide most of the depth cues automatically. This thesis discusses the basic notions required to understand three-dimensional displays. Also discussed are different techniques used to display 3D information and their advantages and disadvantages as well as their current limitations. Several rare-earth doped fluoride crystals that are excited to emit visible light by sequential two ...


All-Optical Regeneration For Phase-Shift Keyed Optical Communication Systems, Kevin Croussore Jan 2007

All-Optical Regeneration For Phase-Shift Keyed Optical Communication Systems, Kevin Croussore

Electronic Theses and Dissertations

All-optical signal processing techniques for phase-shift keyed (PSK) systems were developed theoretically and demonstrated experimentally. Nonlinear optical effects in fibers, in particular four-wave mixing (FWM) that occurs via the ultra-fast Kerr nonlinearity, offer a flexible framework within which numerous signal processing functions can be accomplished. This research has focused on the regenerative capabilities of various FWM configurations in the context of processing PSK signals. Phase-preserving amplitude regeneration, phase regeneration, and phase-regenerative wavelength conversion are analyzed and demonstrated experimentally. The single-pump phase-conjugation process was used to regenerate RZ-DPSK pulse amplitudes with different input noise distributions, and the impact on output phase ...


Frequency Distribution Of Pyroxene Types And A Method To Separate The Composition Of Multiple Pyroxenes In A Sample, Jimmy Allen Davis Jan 2007

Frequency Distribution Of Pyroxene Types And A Method To Separate The Composition Of Multiple Pyroxenes In A Sample, Jimmy Allen Davis

Electronic Theses and Dissertations

Determining mafic mineral composition of asteroid bodies is a topic reviewed by M.J. Gaffey et al. (2002). The iterative procedure discussed can be implemented as an algorithm, and such efforts revealed weaknesses that are examined in this work. We seek to illustrate the limits of this method and graphically determine its predictions. There are boundaries in the formulae given where the equations break down. In ranges where mafic mixtures are predicted, a method is illustrated that allows a decoupling of these mixtures into the constituents.


Design And Demonstration Of Meanderline Retarders At Infrared Frequencies, Jeffrey Scott Tharp Jan 2007

Design And Demonstration Of Meanderline Retarders At Infrared Frequencies, Jeffrey Scott Tharp

Electronic Theses and Dissertations

Meanderline structures are widely used as engineered birefringent materials for waveplates and retarders at radiofrequencies, and have been previously demonstrated at frequencies up to 90 GHz in the millimeter-wave band. In this dissertation, we present results related to the modeling, fabrication, and experimental characterization of meanderlines across the range from 30 to 100 THz, in the long-wave and mid-wave infrared bands. Specific issues addressed in these new designs include spectral dispersion and angular dependence of the retardance, as well as axial ratio and throughput. The impact resulting from the infrared properties of the metals and dielectrics is explicitly included throughout ...


Influence Of Electron Trapping On Minority Carrier Transport Properties Of Wide Band Gap Semiconductors, Olena Tirpak Jan 2007

Influence Of Electron Trapping On Minority Carrier Transport Properties Of Wide Band Gap Semiconductors, Olena Tirpak

Electronic Theses and Dissertations

Minority carrier transport properties and the effects of electron irradiation/injection were studied in GaN and ZnO containing dopants known to form acceptor states deep within the materials' bandgap. Minority carrier diffusion length and lifetime changes were investigated using Electron Beam Induced Current (EBIC) method, cathodoluminescence spectroscopy, spectral photoresponse and persistent photoconductivity measurements. It is shown that electron irradiation by the beam of a scanning electron microscope results in a significant increase of minority carrier diffusion length. These findings are supported by the cathodoluminescence measurements that demonstrate the decay of near-band-edge intensity as a consequence of increasing carrier lifetime under ...


Model Studies Of Time-Dependent Ducting For High-Frequency Gravity Waves And Associated Airglow Responses In The Upper Atmospher, Yonghui Yu Jan 2007

Model Studies Of Time-Dependent Ducting For High-Frequency Gravity Waves And Associated Airglow Responses In The Upper Atmospher, Yonghui Yu

Electronic Theses and Dissertations

This doctoral dissertation has mainly concentrated on modeling studies of shorter period acoustic-gravity waves propagating in the upper atmosphere. Several cases have been investigated in the literature, which are focusing on the propagation characteristics of high-frequency gravity wave packets. The dissertation consists of five main divisions of which each has its own significance to be addressed, and these five chapters are also bridged in order with each other to present a theme about gravity wave ducting dynamics, energetics, and airglows. The first chapter is served as an introduction of the general topic about atmospheric acoustic-gravity waves. Some of the historical ...


Optimization Of Zonal Wavefront Estimation And Curvature Measurements, Weiyao Zou Jan 2007

Optimization Of Zonal Wavefront Estimation And Curvature Measurements, Weiyao Zou

Electronic Theses and Dissertations

Optical testing in adverse environments, ophthalmology and applications where characterization by curvature is leveraged all have a common goal: accurately estimate wavefront shape. This dissertation investigates wavefront sensing techniques as applied to optical testing based on gradient and curvature measurements. Wavefront sensing involves the ability to accurately estimate shape over any aperture geometry, which requires establishing a sampling grid and estimation scheme, quantifying estimation errors caused by measurement noise propagation, and designing an instrument with sufficient accuracy and sensitivity for the application. Starting with gradient-based wavefront sensing, a zonal least-squares wavefront estimation algorithm for any irregular pupil shape and size ...


Surface Characterization Of Thin Film Zno Capacitors By Capacitance-Voltage Measurements, Linda Smith Jan 2007

Surface Characterization Of Thin Film Zno Capacitors By Capacitance-Voltage Measurements, Linda Smith

Electronic Theses and Dissertations

The main objective of the research was the fabrication and characterization of MOS/MIS capacitors with ZnO as the insulating layer. Comparison with the already well known behavior of MOS/MIS capacitors with SiO2 as insulator was used to facilitate determination of the ZnO characteristics. Moreover, thermal annealing of the samples led to increased understanding of the role of defects on the dielectric properties of the ZnO layers in the MOS/MIS devices. Hall-effect transport measurements and x-ray diffraction (XRD) spectroscopy are used to analyze the structure and electronic surface characteristics of the ZnO insulator. Capacitance-voltage (C-V) measurements are used ...


Discrete Surface Solitons, Sergiy Suntsov Jan 2007

Discrete Surface Solitons, Sergiy Suntsov

Electronic Theses and Dissertations

Surface waves exist along the interfaces between two different media and are known to display properties that have no analogue in continuous systems. In years past, they have been the subject of many studies in a diverse collection of scientific disciplines. In optics, one of the mechanisms through which optical surface waves can exist is material nonlinearity. Until recently, most of the activity in this area was focused on interfaces between continuous media but no successful experiments have been reported. However, the growing interest that nonlinear discrete optics has attracted in the last two decades has raised the question of ...


Nonlinear Optical Properties Of Organic Chromophores Calculated Within Time Dependent Density Functional Theory, Sergio Tafur Jan 2007

Nonlinear Optical Properties Of Organic Chromophores Calculated Within Time Dependent Density Functional Theory, Sergio Tafur

Electronic Theses and Dissertations

Time Dependent Density Functional Theory offers a good accuracy/computational cost ratio among different methods used to predict the electronic structure for molecules of practical interest. The Coupled Electronic Oscillator (CEO) formalism was recently shown to accurately predict Nonlinear Optical (NLO) properties of organic chromophores when combined with Time Dependent Density Functional Theory. Unfortunately, CEO does not lend itself easily to interpretation of the structure activity relationships of chromophores. On the other hand, the Sum Over States formalism in combination with semiempirical wavefunction methods has been used in the past for the design of simplified essential states models. These models ...


Three-Dimensional Micron-Scale Metal Photonic Crystals Via Multi-Photon Direct Laser Writing And Electroless Metal Deposition, Amir Tal Jan 2007

Three-Dimensional Micron-Scale Metal Photonic Crystals Via Multi-Photon Direct Laser Writing And Electroless Metal Deposition, Amir Tal

Electronic Theses and Dissertations

Three-dimensional (3D) metal photonic crystals (MPCs) can exhibit interesting electromagnetic properties such as ultra-wide photonic or "plasmonic" band gaps, selectively tailored thermal emission, extrinsically modified absorption, and negative refractive index. Yet, optical-wavelength 3D MPCs remain relatively unexplored due to the challenges posed by their fabrication. This work explores the use of multi-photon direct laser writing (DLW) coupled with electroless metallization as a means for preparing MPCs. Multi-photon DLW was used to prepare polymeric photonic crystal (PC) templates having a targeted micron-scale structure and form. MPCs were then created by metallizing the polymeric PCs via wet-chemical electroless deposition. The electromagnetic properties ...


Effects Of Polarization And Coherence On The Propagation And The Detection Of Stochastic Electromagnetic Beams, Mohamed Fouad Salem Jan 2007

Effects Of Polarization And Coherence On The Propagation And The Detection Of Stochastic Electromagnetic Beams, Mohamed Fouad Salem

Electronic Theses and Dissertations

Most of the physically realizable optical sources are radiating in a random manner given the random nature of the radiation of a large number of atoms that constitute the source. Besides, a lot of natural and synthetic materials are fluctuating randomly. Hence, the optical fields that one encounters, in most of the applications are fluctuating and must be treated using random or stochastic functions. Within the framework of the scalar-coherence theory, one can describe changes of the properties of any stochastic field such as the spectral density and the spectral degree of coherence on propagation in any linear medium, deterministic ...


Experimental Study Of Profiles Of Implanted Species Into Semiconductor Materials Using Secondary Ion Mass Spectrometry, Fatma Salman Jan 2007

Experimental Study Of Profiles Of Implanted Species Into Semiconductor Materials Using Secondary Ion Mass Spectrometry, Fatma Salman

Electronic Theses and Dissertations

The study of impurity diffusion in semiconductor hosts is an important field that has both fundamental appeal and practical applications. Ion implantation is a good technique to introduce impurities deep into the semiconductor substrates at relatively low temperature and is not limited by the solubility of the dopants in the host. However ion implantation creates defects and damages to the substrate. Annealing process was used to heal these damages and to activate the dopants. In this study, we introduced several species such as alkali metals (Li, Na, K), alkali earth metals (Be, Ca,), transition metals (Ti, V, Cr, Mn) and ...