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Articles 181 - 210 of 349
Full-Text Articles in Optics
Implementation Of Branch-Point-Tolerant Wavefront Reconstructor For Strong Turbulence Compensation, Michael J. Steinbock
Implementation Of Branch-Point-Tolerant Wavefront Reconstructor For Strong Turbulence Compensation, Michael J. Steinbock
Theses and Dissertations
Branch points arise in optical transmissions due to strong atmospheric turbulence, long propagation paths, or a combination of both. Unfortunately, these conditions are very often present in desired operational scenarios for laser weapon systems, optical communication, and covert imaging, which suffer greatly when traditional adaptive optics systems either cannot sense branch points or implement non-optimal methods for sensing and correcting branch points. Previous research by Pellizzari presented a thorough analysis of various novel branch point tolerant reconstructors in the absence of noise. In this research a realistic model of the Air Force Institute of Technology's adaptive optics system is developed …
Application Of An Imaging Fourier-Transform Spectrometer For The Means Of Combustion Diagnostics, Michael R. Rhoby
Application Of An Imaging Fourier-Transform Spectrometer For The Means Of Combustion Diagnostics, Michael R. Rhoby
Theses and Dissertations
A passive remote sensing technique for accurately monitoring the combustion efficiency of petrochemical flares is greatly desired. A Phase II DOE-funded SBIR lead by Spectral Sciences, Inc. is underway to develop such a method. This paper presents an overview of the progress of AFIT's contribution. A Telops Hyper-Cam Mid-wave infrared imaging Fourier-transform spectrometer is used to examine a flame produced by a Hencken burner. Ethylene fuel was burned at four different equivalency ratios φ = 0:80; 0:91; 1:0 and 1:25. Presented is qualitative spectrally-resolved visualization of a Hencken burner flame and the spatial distribution of combustion by-products. The flame spectra …
Remote Sensing Phase Fluorimetry Using Mercury Vapor Lamp, Matthew J. Bohn, Michael A. Lundin
Remote Sensing Phase Fluorimetry Using Mercury Vapor Lamp, Matthew J. Bohn, Michael A. Lundin
AFIT Patents
An efficient and portable method for remote detection of a target mineral material through frequency domain fluorimetry, a detection technique that measures the time lag between absorption and emission of photons, thereby determining the lifetime of said target mineral material. As claimed and disclosed in the present invention, mercury vapor lamps, a common source of industrial facility lighting, emit radiation that overlaps the UV/blue absorption spectrum of many fluorophores and may be used as an efficient and portable excitation source for remote frequency domain fluorimetry.
The Focusing Of Light Scattered From Diffuse Reflectors Using Phase Modulation, Jessica M. Schafer
The Focusing Of Light Scattered From Diffuse Reflectors Using Phase Modulation, Jessica M. Schafer
Theses and Dissertations
“Indirect photography" was recently demonstrated for imaging hidden scene information through the collection and radiometric modeling of light reflecting off of visible reflecting surfaces. The ability to focus the beam that reflects off the visible surface to a tight spot on the hidden object is theorized to simulate a direct line of sight from the light source to the object, reducing the radiometric model to that of the previously demonstrated dual photography. Experiments involving the focusing of light transmitted through highly scattering media have been adapted to the case of reflection. The focusing of a HeNe laser reflected off diffusely …
Matrix Determination Of Reflectivity Of Hidden Object Via Indirect Photography, Simon S. Ferrel
Matrix Determination Of Reflectivity Of Hidden Object Via Indirect Photography, Simon S. Ferrel
Theses and Dissertations
Indirect photography is a recently demonstrated technique which expands on the principles of dual photography and allows for the imaging of hidden objects. A camera and light source are collocated with neither having line-of-sight access to the hidden object. Light from the source, a laser, is reflected off a visible non-specular surface onto the hidden object, where it is reflected back to the initial non-specular surface and collected by the camera. This process may be repeated numerous times for various laser spot positions to yield slightly different camera images due to a variation in the illumination of the object. These …
Electrical And Optical Characterization Of Si-Ge-Sn, Merle D. Hamilton
Electrical And Optical Characterization Of Si-Ge-Sn, Merle D. Hamilton
Theses and Dissertations
The electrical characterization of boron-doped p-Si0.08Ge0.90Sn0.02/p-Ge(100) and p-Si0.112Ge0.86Sn0.028/n-Si(100) with various epilayer thicknesses was measured using the Hall effect. The room temperature sheet carrier concentration ranged from 1.21 x 1013 – 1.32 x 1016 cm-2. The room temperature mobilities were measured to be between 166 and 717 cm2/V·s, depending on sample composition. In the low temperature regime, the mobility was mainly affected by ionized impurity scattering. In the high temperature regime, the mobility was mainly affected by …
Characterization Of A Hyperspectral Chromotomographic Imaging Ground System, Chad B. Su'e
Characterization Of A Hyperspectral Chromotomographic Imaging Ground System, Chad B. Su'e
Theses and Dissertations
A field-deployable hyperspectral chromotomographic imager has been developed and tested as a risk-reduction prototype to assist design of a space-based system. The instrument uses a high-speed video camera looking through a rotating direct-vision prism to simultaneously observe the full field of view in all visible wavelength channels. The chromotomographic process multiplexes the spectral and spatial so an advanced reconstruction algorithm is required to separate the spectral channels. A physics-based model of the instrument was developed to assist in future trade-space choices for design of the spaced-based system. Additionally, the model is used for the development and assessment of the filtered …
Fdtd Simulation Of Novel Polarimetric And Directional Refelectance And Transmittance Measurements From Optical Nano- And Micro-Structured Materials, Spencer R. Sellers
Fdtd Simulation Of Novel Polarimetric And Directional Refelectance And Transmittance Measurements From Optical Nano- And Micro-Structured Materials, Spencer R. Sellers
Theses and Dissertations
The basic physics of nano-/micro-structured materials must be categorized through measurements and simulation to fully understand their scatter dependence on polarization and angle on incidence before they can be considered for war fighter applications. The off-normal incidence and polarization dependant scatter for a guided-mode resonance filter (GMRF) and a surface plasmonic polariton (SPP) extraordinary transmission filter is measured. The measurements are compared to finite-difference time domain (FDTD) simulations. The GMRF is found to exhibit extraordinary angular scatter at the resonant coupled modes. An approximation is developed to predict the dependence of these modes on wavelength, incident angle and polarization. For …
3-D Scene Reconstruction From Aerial Imagery, Jared M. Ekholm
3-D Scene Reconstruction From Aerial Imagery, Jared M. Ekholm
Theses and Dissertations
3-D scene reconstructions derived from Structure from Motion (SfM) and Multi-View Stereo (MVS) techniques were analyzed to determine the optimal reconnaissance flight characteristics suitable for target reconstruction. In support of this goal, a preliminary study of a simple 3-D geometric object facilitated the analysis of convergence angles and number of camera frames within a controlled environment. Reconstruction accuracy measurements revealed at least 3 camera frames and a 6 convergence angle were required to achieve results reminiscent of the original structure. The central investigative effort sought the applicability of certain airborne reconnaissance flight profiles to reconstructing ground targets. The data sets …
Internal Electric Fields Due To Piezoelectric And Spontaneous Polarizations In Cdzno/Mgzno Quantum Well, H. C. Jeon, S. J. Lee, Tae Won Kang, S. H. Park, Yung Kee Yeo, T. F. George
Internal Electric Fields Due To Piezoelectric And Spontaneous Polarizations In Cdzno/Mgzno Quantum Well, H. C. Jeon, S. J. Lee, Tae Won Kang, S. H. Park, Yung Kee Yeo, T. F. George
Faculty Publications
We have investigated optical properties as a function of internal and external fields in the quantum well (QW). Optical properties of CdZnO/MgZnO QW structures are investigated by using many‐body effects. The CdZnO/MgZnO QW structure with high Cd composition is found to have smaller optical gain because the strain‐induced piezoelectric polarization and the spontaneous polarization in the well increase with the inclusion of Cd. These results demonstrate that high performance laser diode operation can be realized in CdZnO/MgZnO QW structures by reducing those polarizations adopting dipole reverse method.
Background-Oriented Schlieren Pattern Optimization, Jeffery E. Hartberger
Background-Oriented Schlieren Pattern Optimization, Jeffery E. Hartberger
Theses and Dissertations
This paper describes a test series to investigate background patterns used for the Background-Oriented Schlieren field density measurement technique. Several varying background patterns were substituted under similar fluid density conditions to visualize and isolate the effects of patterns in the background images. A qualitative comparison was completed of the flow visualization results of each background pattern to categorize background conditions that improved the flow visualization image. Changes in background patterns revealed significant changes in flow visualization. Pattern contrast, spacing and sizing all played large parts in the quality of the visual density gradient imaging during the test series.
Integrated Approach To Free Space Optical Communications In Strong Turbulence, Jason A. Tellez
Integrated Approach To Free Space Optical Communications In Strong Turbulence, Jason A. Tellez
Theses and Dissertations
The propagation of a free space optical communication signal through atmospheric turbulence experiences random fluctuations in intensity, including signal fades which negatively impact the communications link performance. This research develops an analytical probability density function (PDF) to model the best case scenario of using multiple independent beams to reduce the intensity fluctuations. The PDF was further developed to account for partially correlated beams, such as would be experienced by beams having finite separation. The PDF was validated with results obtained from digital simulations as well as lab experiments. The research showed that as the number of transmitted beams increases the …
Modeling Self-Referencing Interferometers With Extended Beacons And Strong Turbulence, Daniel J. Wheeler
Modeling Self-Referencing Interferometers With Extended Beacons And Strong Turbulence, Daniel J. Wheeler
Theses and Dissertations
The overall purpose of this research was to better understand the performance of a self-referencing interferometer (SRI) when used with extended beacons in strong atmospheric turbulence. It was performed by assuming the extended beacon could be modeled as a Gaussian Schell-model beam, then analyzing the effect of propagating this beam through strong atmospheric turbulence. Since the operation of an SRI requires coupling this light into a single-mode optical fiber, analytic expressions of the mean and normalized variance of the coupling efficiency were derived. An improved noise model for the SRI was then developed that included all potential noise sources such …
Optical Flow-Based Odometry For Underground Tunnel Exploration, Terra Kier
Optical Flow-Based Odometry For Underground Tunnel Exploration, Terra Kier
Theses and Dissertations
As military operations in degraded or GPS-denied environments continue to increase in frequency and importance, there is an increased necessity to be able to determine precision location within these environments. Furthermore, authorities are finding a record number of tunnels along the U.S.-Mexico border; therefore, underground tunnel characterization is becoming a high priority for U.S. Homeland Security as well. This thesis investigates the performance of a new image registration technique based on a two camera optical- flow configuration using phase correlation techniques. These techniques differ from other image based navigation methods but present a viable alternative increasing autonomy and answering the …
Estimating Anthropometric Marker Locations From 3-D Ladar Point Clouds, Matthew J. Maier
Estimating Anthropometric Marker Locations From 3-D Ladar Point Clouds, Matthew J. Maier
Theses and Dissertations
An area of interest for improving the identification portion of the system is in extracting anthropometric markers from a Laser Detection and Ranging (LADAR) point cloud. Analyzing anthropometrics markers is a common means of studying how a human moves and has been shown to provide good results in determining certain demographic information about the subject. This research examines a marker extraction method utilizing principal component analysis (PCA), self-organizing maps (SOM), alpha hulls, and basic anthropometric knowledge. The performance of the extraction algorithm is tested by performing gender classification with the calculated markers.
Development Of An Interference Lithography Capability Using A Helium Cadmium Ultraviolet Multimode Laser For The Fabrication Of Sub-Micron-Structured Optical Materials, Stanley D. Crozier
Development Of An Interference Lithography Capability Using A Helium Cadmium Ultraviolet Multimode Laser For The Fabrication Of Sub-Micron-Structured Optical Materials, Stanley D. Crozier
Theses and Dissertations
The goal of this work is to develop unique holograms on a semiconductor-metal thin films to characterize as potential metamaterials. This is achievable by developing a fabrication recipe to include exposure methods, exposure dosages, and material development. This study developed an interference lithography capability at AFIT for the first time with period resolution below 230nm. It also identified initial acceptable photoresist materials and exposure dosages, and a path to follow to optimize this process. The potential impact of this is to make IL a standard in optical meta-material fabrication, which decreases manufacturing time and allows for less error in production. …
Simulating The Effects Of An Extended Source On The Shack-Hartmann Wavefront Sensor Through Turbulence, Jeffery S. Dennison
Simulating The Effects Of An Extended Source On The Shack-Hartmann Wavefront Sensor Through Turbulence, Jeffery S. Dennison
Theses and Dissertations
Perspective elongation in Shack-Hartmann wavefront sensor (SHWFS) spots is a phenomenon caused by an extended three-dimensional scattering beacon in the mesosphere (80-100km). Elongated spots cause errors in wavefront sensor measurements, which leads to poor turbulence compensation and decreased image resolution of the optical system. In order to compensate for elongated spots, a proper beacon model must be developed to simulate the error. In this paper, a documented theory for modeling an elongated sodium beacon and elongated SHWFS spots using sodium layer slices was tested. It was found that nine evenly-spaced slices were adequate to model the elongated beacon in the …
Shack-Hartmann And Interferometric Hybrid Wavefront Sensor, Troy R. Ellis
Shack-Hartmann And Interferometric Hybrid Wavefront Sensor, Troy R. Ellis
Theses and Dissertations
This document reports results of wave-optics simulations used to test the performance of a hybrid wavefront sensor designed to combine the self-referencing interferometer and Shack-Hartmann wavefront sensors in an optimal way. Optimal hybrid-wavefront sensor design required a thorough analysis of the noise characteristics of each wavefront sensor to produce noise models that assist in the design of an optimal phase-estimation algorithm. Feasible architectures and algorithms for combining wavefront sensors were chosen, and the noise models of the individual wavefront sensors were combined to form a model for the noise-induced error of the resulting hybrid sensor. The hybrid wavefront sensor and …
A Statistical Approach To Fusing 2-D And 3-D Ladar Systems, Paul F. Dolce
A Statistical Approach To Fusing 2-D And 3-D Ladar Systems, Paul F. Dolce
Theses and Dissertations
LADAR (LAser Detection and Ranging) systems can be used to provide 2-D and 3-D images of scenes. Generally, 2-D images possess superior spatial resolution but without range data due to the density of their focal plane arrays. A 3-D LADAR system can produce range to target data at each pixel, but lacks the 2-D system's superior spatial resolution. The 3-D system is limited by its hardware, specifically its imaging array. Currently developers are investigating ways to change the pixel size in the 3-D LADAR imaging array, but the costs of this research is quite expensive and technically robust. It is …
Polarimetric Enhancements To Electro-Optical Aided Navigation Techniques, Jeremiah D. Johnson
Polarimetric Enhancements To Electro-Optical Aided Navigation Techniques, Jeremiah D. Johnson
Theses and Dissertations
Navigation in indoor and urban environments by small unmanned systems is a topic of interest for the Air Force. The Advanced Navigation Technology Center at the Air Force Institute of Technology is continually looking for novel approaches to navigation in GPS deprived environments. Inertial sensors have been coupled with image aided concepts, such as feature tracking, with good results. However, feature density in areas with large, flat, smooth surfaces tends to be low. Polarimetric sensors have been used for surface reconstruction, surface characterization and outdoor navigation. This thesis combines aspects of some of these algorithms along with a realistic, micro-facet …
A Multispectral Bidirectional Reflectance Distribution Function Study Of Human Skin For Improved Dismount Detection, Bradley M. Koch
A Multispectral Bidirectional Reflectance Distribution Function Study Of Human Skin For Improved Dismount Detection, Bradley M. Koch
Theses and Dissertations
In 2008, the Sensors Exploitation Research Group at the Air Force Institute of Technology began using spectral properties of skin for the detection and classification of humans. Since then a multispectral skin detection system was developed to exploit the optical properties of human skin at wavelengths in the visible and near infrared region of the electromagnetic spectrum. A rules-based detector, analyzing an image spectrally, currently bases its skin pixel selection criteria on a diffuse skin reflectance model. However, when observing skin in direct view of the sun, a glint of light off skin is common and indicates specularity. The areas …
Optical Metamaterial Design, Fabrication And Test, Jack P. Lombardi
Optical Metamaterial Design, Fabrication And Test, Jack P. Lombardi
Theses and Dissertations
Metamaterials, materials that make use of naturally occurring materials and designed structures to create materials with special properties not found in nature, are a fascinating new area of research, combining the fields of physics, microfabrication, and material science. This work will focus on the development of metamaterials operating in the visible and infrared which will be constructed and tested for basic optical properties. Possible applications for these materials will not be investigated. The this work will go into the fabrication and test of layered metal-dielectric structures, called layered metamaterials, as these structures hold potential for applications in advanced optical systems. …
Effect Of Coudé Pupil Rotation On Sodium Laser Beacon Perspective Elongation, Russell J. Mcguigan
Effect Of Coudé Pupil Rotation On Sodium Laser Beacon Perspective Elongation, Russell J. Mcguigan
Theses and Dissertations
This research models a sodium laser guide star and its measurement by a Shack-Hartmann wavefront sensor. By predicting the extent of beacon elongation and Coude rotation, reference images are produced for each subaperture throughout an engagement scenario. These reference sources are then used to continuously recalibrate the system as it changes orientation. This model measures the effect of perspective elongation and Coude on SHWFS measurements to quantitatively determine the extent of degradation that occurs.
Diffusion Of Rubidium Vapor Through Hollow-Core Fibers For Gas-Phase Fiber Lasers, Eric M. Guild
Diffusion Of Rubidium Vapor Through Hollow-Core Fibers For Gas-Phase Fiber Lasers, Eric M. Guild
Theses and Dissertations
This work examines the diffusion of rubidium through a small diameter tube alone and in the presence of noble gases. A fluid dynamics analysis is investigated to aid in choosing a method for transferring atomic rubidium vapor that is reliable and efficient. Solutions to the time dependant ordinary differential equation describing the experimental flow properties of the system reveal more precise outcomes than previously practiced routines. Resolved viscosities and Poiseuille flow theory velocity profile distributions are characterized for noble gas carriers of the rubidium vapor. Applying Reynolds Numbers to the flow experiments provides pressure differential boundaries that are employed in …
Branch Point Mitigation Of Thermal Blooming Phase Compensation Instability, Mark F. Spencer
Branch Point Mitigation Of Thermal Blooming Phase Compensation Instability, Mark F. Spencer
Theses and Dissertations
Thermal blooming can have a major impact on high-energy laser (HEL) beam propagation in the atmosphere. In theory, an adaptiveoptics (AO) system can mitigate the nonlinear optical effects induced by thermal blooming; however, when a single deformable mirror is used for phase-only compensation, analysis predicts the possibility of instability. This instability is appropriately termed phase compensation instability (PCI) and arises with the time-dependent development of spatial perturbations found within the HEL beam. These spatial perturbations act as local hot spots that produce negative-lens-like optical effects in the atmosphere. An AO system corrects for the hot spots by applying positive-lens-like phase …
Optical And Electrical Characterization Melt-Grown Bulk Ingaas And Inasp, Jean W. Wei
Optical And Electrical Characterization Melt-Grown Bulk Ingaas And Inasp, Jean W. Wei
Theses and Dissertations
A new method to determine semiconductor bandgap energy directly from the easily measured transmission spectra was developed. The method was verified using many binary semiconductors with known properties and utilized to determine the unknown ternary semiconductors were determined at various wavelengths and temperatures. Photoluminescence and Hall-effect measurement were performed to identify various electronic transitions, as well as sample quality. The determination of electrical and optical properties of the material will provide important addition to the database of material properties for future optoelectronic device applications. In the near future, newer materials and their applications need to be developed, and often binary …
Shock Wave Dynamics Of Novel Aluminized Detonations And Empirical Model For Temperature Evolution From Post-Detonation Combustion Fireballs, Joe Motos Gordon
Shock Wave Dynamics Of Novel Aluminized Detonations And Empirical Model For Temperature Evolution From Post-Detonation Combustion Fireballs, Joe Motos Gordon
Theses and Dissertations
This research characterizes the blast wave and temperature evolution of an explosion fireball in order to improve the classification of aluminized conventional munitions based on a single explosive type such as RDX. A drag model fit to data shows initial shock velocities of 1.6-2.8 km/s and maximum fireball radii ranging from 4.3-5.8 m with most of the radii reached by 50 ms upon detonation. The Sedov-Taylor point blast model is fitted to data where a constant release (s=1) of energy upon detonation suggests shock energies of 0.5-8.9 MJ with blast dimensionalities indicative of the spherical geometry (n3) observed in visible …
Tunable Optical Delay In Doppler-Broadened Cesium Vapor, Monte D. Anderson
Tunable Optical Delay In Doppler-Broadened Cesium Vapor, Monte D. Anderson
Theses and Dissertations
Variable-delay tunable optical delay line or optical buffers are critical for the development of all-optical networks components as well as interferometry and analytic instruments. Recent research on slow light may hold the key for the development of the first practical tunable optical delay device. In this research the linear dispersion delay effects in an alkali vapor. The hyperfine relaxation observations present insight into the complex bleach wave dynamics during a high-intensity pulsed pump in DPAL systems.
Laser Demonstration And Performance Characterization Of An Optically Pumped Alkali Laser System, Clifford V. Sulham
Laser Demonstration And Performance Characterization Of An Optically Pumped Alkali Laser System, Clifford V. Sulham
Theses and Dissertations
Diode Pumped Alkali Lasers (DPALs) offer a promising approach for high power lasers in military applications that will not suffer from the long logistical trails of chemical lasers or the thermal management issues of diode pumped solid state lasers. This research focuses on characterizing a DPAL-type system to gain a better understanding of using this type of laser as a directed energy weapon. A rubidium laser operating at 795 nm is optically pumped by a pulsed titanium sapphire laser to investigate the dynamics of DPALs at pump intensities between 1.3 and 45 kW/cm2. Linear scaling as high as …
Electronic Structure Of Lithium Tetraborate, David J. Wooten
Electronic Structure Of Lithium Tetraborate, David J. Wooten
Theses and Dissertations
Due to interest as neutron detection material, an investigation of Li2B4O7(110) and Li2B4O7(100) was undertaken, utilizing photoemission and inverse photoemission spectroscopic techniques. The measured band gap depended on crystallographic direction with the band gaps ranging from 8.9±0.5 eV to 10.1±0.5 eV. The measurement yielded a density of states that qualitatively agreed with the theoretical results from model bulk band structure calculations for Li2B4O7; albeit with a larger band gap than predicted, but consistent with the known deficiencies of LDA and DFT calculations. …