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Articles 1 - 17 of 17
Full-Text Articles in Physics
Closed-Loop Adaptive Optics Control In Strong Atmospheric Turbulence, Todd M. Venema
Closed-Loop Adaptive Optics Control In Strong Atmospheric Turbulence, Todd M. Venema
Theses and Dissertations
A self-referencing interferometer based closed-loop adaptive optics controller is developed which is designed to operate effectively under strong turbulence conditions. The aberrated optical field is modeled stochastically and then estimates of the state of the system are developed using a steady-state, fixed-gain Kalman filter. The phase of the optical field is considered the state of the system which is wrapped in a limited range of (-π, π]. This phase is unwrapped through the use of a least-squares reconstructor which has been modified to work effectively in the presence of branch points associated with strong turbulence. The conjugate of the optical …
Electronic State Distributions Of Y Ba2Cu3O7-X Laser Ablated Plumes, Patrick D. Kee
Electronic State Distributions Of Y Ba2Cu3O7-X Laser Ablated Plumes, Patrick D. Kee
Theses and Dissertations
The application of spectral and imagery diagnostics to YBa2Cu3O7 (YBCO) laser-ablated plumes was systematically studied to determine their effectiveness for process control. Emission signatures were collected for plumes created by ablating bulk YBCO with a pulsed laser source. A KrF (λ=248 nm) laser source operating at 4-10 J/cm2 at a 4-10 Hz pulse repetition frequency was used to ablate a bulk YBCO target at O2 background pressures ranging from 50 to 400 mTorr. Emission spectra were collected over the 500 to 860 nm bandpass at distances from the target ranging from 31.4 to …
A Study Of The Irradiance-And-Temperature-Dependence Of Mid-Wave-Infrared (Mwir)Absorption In Indium Antimonide (Insb), John M. Callahan
A Study Of The Irradiance-And-Temperature-Dependence Of Mid-Wave-Infrared (Mwir)Absorption In Indium Antimonide (Insb), John M. Callahan
Theses and Dissertations
This work entails further investigation of the absorption of photons in indium antimonide (InSb). Previously work at the Air Force Institute of Technology (AFIT) attributed laser blooming effects in InSb focal plane arrays (FPA’s) to the Burstein-Moss effect. The contributing effect is from a decrease in the absorption of the InSb material, such that the transmitted optical energy scatters off the integrated circuitry beneath the InSb thin film back into the optical system. To evaluate this, irradiance-dependent laser-absorption experiments were performed on thinned, InSb wafers prior to their FPA fabrication. The samples were illuminated with a focused CO2 laser at …
Stimulated Brillouin Scattering Phase Conjugation In Fiber Optic Waveguides, Steven M. Massey
Stimulated Brillouin Scattering Phase Conjugation In Fiber Optic Waveguides, Steven M. Massey
Theses and Dissertations
The objective of this research effort was to demonstrate the path to continuous wave, coherent beam combination through stimulated Brillouin scattering phase conjugation in optical fiber. This work experimentally determined the fiber parameters necessary for phase conjugation in step-index optical fiber. Continuous wave phase conjugation using stimulated Brillouin scattering in step-index fibers was achieved for the first time with a fidelity of 0.8 and a threshold power of 16 W in a 15-m fiber with 0.13 NA. A fidelity of 0.8 was also achieved using 40 m of fiber with 0.06-NA and a threshold power of 15 W. The fidelity …
Characterizing Effects And Benefits Of Beam Defocus On High Energy Laser Performance Under Thermal Blooming And Turbulence Conditions For Air-To-Ground Engagements, Scott N. Long
Theses and Dissertations
This dissertation makes contributions towards knowledge of optimizing of laser weapon performance when operating in the air-to-ground (ATG) regime in thermal blooming conditions. Wave optics modeling techniques were used to represent laser weapon performance in a high fidelity sense to allow progress to be made toward improving lower-fidelity scaling laws that can be used in systems level analysis which has need for better representations of thermal blooming. Chemical-oxygen iodine laser (COIL) based weapon systems that operate near the ground will experience thermal blooming due to atmospheric absorption if output power is sufficiently high. The thermal lens in the ATG case …
Tightly Integrating Optical And Inertial Sensors For Navigation Using The Ukf, Sedat Ebcin
Tightly Integrating Optical And Inertial Sensors For Navigation Using The Ukf, Sedat Ebcin
Theses and Dissertations
The motivation of this research is to address the benefits of tightly integrating optical and inertial sensors where GNSS signals are not available. The research begins with describing the navigation problem. Then, error and measurement models are presented. Given a set of features, a feature detection and projection algorithm is developed which utilizes inertial measurements to predict vectors in the feature space between images. The unscented Kalman filter is applied to the navigation system using the inertial measurements and feature matches to estimate the navigation trajectory. Finally, the image-aided navigation algorithm is tested using a simulation and an experiment. As …
Analysis Of Non-Uniform Gain For Control Of A Deformable Mirror In An Adaptive-Optics System, Kevin P. Vitayaudom
Analysis Of Non-Uniform Gain For Control Of A Deformable Mirror In An Adaptive-Optics System, Kevin P. Vitayaudom
Theses and Dissertations
The Air Force Research Laboratory’s Sodium Guidestar Adaptive Optics for Space Situational Awareness program (NGAS) has sponsored research on spatially non-uniform gain for the servo-loop controller of an adaptive optics (AO) system. The edge subapertures of a Shack-Hartmann wavefront sensor have lower signal-to-noise ratios and are more susceptible to measurement errors than fully illuminated center subapertures. These measurement errors produce errant commands over the corresponding edge actuators and can induce instabilities over these regions in strong turbulence conditions. The objective of this research was to develop and experimentally verify the use of spatially varying gain maps on the servo-loop controller …
Demonstration Of A Strategy To Perform Two-Dimensional Diode Laser Tomography, Ryan N. Givens
Demonstration Of A Strategy To Perform Two-Dimensional Diode Laser Tomography, Ryan N. Givens
Theses and Dissertations
Demonstration of a strategy to perform two-dimensional diode laser tomography using a priori knowledge from symmetry arguments and computational fluid dynamic (CFD) calculations is presented for a flat flame burner. The strategy uses an optimization technique to determine flame diameter and location using a vector quantization approach. Next, the variance in a training set, produced from CFD calculations, is captured using principal components analysis. The information in the training set allows interpolation between beam paths resulting in temperature and density maps. Finally, the TDLAS temperature and density maps are shown to agree with traditional thermocouple measurements of the flat flame …
An Image Based Bidirectional Reflectivity Distribution Function Experiment, Michael T. Hagg
An Image Based Bidirectional Reflectivity Distribution Function Experiment, Michael T. Hagg
Theses and Dissertations
The temperature dependence of Bidirectional Reflectivity Distribution Functions (BRDFs) is not well documented. For the sake of time and customer demand, current measurements are taken at room temperature, but the reflectivity of a material changes as a function of temperature. The assumption is that this change is uniform, and as such, the BRDF will retain its relative angular shape but perhaps be scaled in magnitude as a function of temperature. When BRDFs are to be used at elevated temperatures, a scaling factor is then applied. In addition, BRDF as a function of rate of change of temperature has been identified …
Modeling Of Sbs Phase Conjugation In Multimode Step Index Fibers, Justin B. Spring
Modeling Of Sbs Phase Conjugation In Multimode Step Index Fibers, Justin B. Spring
Theses and Dissertations
Stimulated Brillouin scattering in a multimode step-index fiber can be used to generate a counter-propagating, phase-conjugate beam that would prove useful in many applications, such as near diffraction limited, double-pass high-power amplifiers or coherent beam combination. Relatively little modeling of such a fiber-based phase conjugator has been done, making design decisions regarding type and length of fiber largely guesswork. A numerical model was constructed with the aim of providing educated predictions about the phase conjugate fidelity that could be expected from a given pump intensity input coupled into a specific fiber. A numerical perturbation algorithm was constructed to search for …
Modulation Response Of Twin Optically Coupled Diode Lasers, Eric M. Golden
Modulation Response Of Twin Optically Coupled Diode Lasers, Eric M. Golden
Theses and Dissertations
Diode lasers are useful in military and commercial applications that have strict requirements for size, weight and power. This includes the use of diode lasers in optoelectronic and photonic integrated circuits, which can lead to new technologies in optical communications and optical interconnects in high performance computing systems. For these systems to be effective, the diode laser must be modulated at frequencies beyond current limits which are typically a few GHz. This barrier can be broken by optically coupling a diode laser with a similar laser. A set of single mode rate equations models the dynamics of twin optically coupled …
Collision Avoidance For Uavs Using Optic Flow Measurement With Line Of Sight Rate Equalization And Looming, Paul J. Shelnutt
Collision Avoidance For Uavs Using Optic Flow Measurement With Line Of Sight Rate Equalization And Looming, Paul J. Shelnutt
Theses and Dissertations
A series of simplified scenarios is investigated whereby an optical flow balancing guidance law is used to avoid obstacles by steering an air vehicle between fixed objects/obstacles. These obstacles are registered as specific points that can be representative of features in a scene. The obstacles appear in the field of view of a single forward looking camera. First a 2-D analysis is presented where the rate of the line of sight from the vehicle to each of the obstacles to be avoided is measured. The analysis proceeds by initially using no field of view (FOV) limitations, then applying FOV restrictions, …
Ultrafast Spectroscopy Of Mid-Infrared Semiconductors Using The Signal And Idler Beams Of A Synchronous Optical Parametric Oscillator, Richard M. Derbis
Ultrafast Spectroscopy Of Mid-Infrared Semiconductors Using The Signal And Idler Beams Of A Synchronous Optical Parametric Oscillator, Richard M. Derbis
Theses and Dissertations
Mid-Wave Infrared (MWIR) semiconductors are of use to the Air Force for several applications. Ultrafast spectroscopy can be used to better quantify the effectiveness of semiconductor opto-electronic devices. The objective of this thesis was to improve the procedure for taking ultrafast, time-resolved measurements of photoluminescence from MWIR semiconductors. Previous work has used a mode-locked titanium sapphire (Ti:Saph) laser to excite the semiconductor sample and to upconvert the photoluminescence from the semiconductor. Work completed in this thesis improved on the techniques developed during previous work. A synchronous Optical Parameter Oscillator (OPO) will be used to convert the Ti:Saph laser (0.830 µm) …
Limitations Of Segmented Wavefront Control Devices In Emulating Optical Turbulence, Michael D. Plourde
Limitations Of Segmented Wavefront Control Devices In Emulating Optical Turbulence, Michael D. Plourde
Theses and Dissertations
Using a device to act as a surrogate for atmospheric turbulence in a laboratory is necessary to build and test optical systems for imaging, lidar, laser weapons, and laser communications. Liquid-crystal spatial light modulators (LC SLMs) and segmented micro-electro-mechanical-system (MEMS) deformable mirrors (DMs) are commonly used devices for altering wavefronts in order to simulate a portion of atmospheric turbulence. The best location of these devices was theoretically analyzed to obtain the broadest possible range of atmospheric conditions. It was found that two phase screens should be placed at the beginning of the optical path to achieve maximum turbulence strength for …
Measuring Dispersion In Laser Cavity Mirrors Using White-Light Interferometry, Allison S. Goodspeed
Measuring Dispersion In Laser Cavity Mirrors Using White-Light Interferometry, Allison S. Goodspeed
Theses and Dissertations
Terahertz radiation is an emerging field that has far reaching applications. There is a need for portable and affordable terahertz sources that may be used for detection of structural weaknesses in aerospace composites. One possibility for terahertz generation is a femtosecond Cr:LiSAF laser. However, controlling intracavity dispersion is necessary in order to get the ultrashort pulses needed to generate terahertz radiation. This research measures dispersion of the chirped femtosecond intracavity mirrors by employing white-light interferometry and explains the theory behind the curve-fitting process used to calculate dispersion. To compensate for the narrow reflectivity band of the mirrors, a CaF2 …
Nonmechanical Multizoom Telescope Design Using A Liquid Crystal Spatial Light Modulator And Focus-Correction Algorithm, Eric W. Thompson
Nonmechanical Multizoom Telescope Design Using A Liquid Crystal Spatial Light Modulator And Focus-Correction Algorithm, Eric W. Thompson
Theses and Dissertations
Theoretical development and design of a compact nonmechanical multi-zoom telescope system is presented. A liquid crystal spatial light modulator (LC SLM) enables selection of four separate beam paths without the use of moving parts. Each path incurs a different focus aberration in the image plane that can be deconvolved with postprocessing to yield four possible corrected magnification options. To increase flexibility, each region has a 40-wave subrange of focus. Optical zooms of up to 10 times magnification are feasible and are limited only by system noise and signal to noise ratio. Elimination of moving parts for focus could prove beneficial …
Production And Characterization Of Femtosecond-Laser-Induced Air Plasma, David R. Armbruster
Production And Characterization Of Femtosecond-Laser-Induced Air Plasma, David R. Armbruster
Theses and Dissertations
The purpose of this research was to produce, characterize, and optimize laser induced air plasma as a preliminary step in using the plasma as a source of terahertz radiation. An 800 nanometer, 50 femtosecond, 0.75 Watt, pulsed Ti:Sapphire laser system was used as the source infrared beam. A beam expander was used to expand the beam to a diameter of approximately 6.5 mm, and the beam was focused through a 25 mm focal length achromatic lens to produce laser-induced plasma in ambient air. A 40 kHz ultrasonic transducer was used to detect the plasma. A second harmonic generation crystal was …