Department: Electro-Optics ![[clear]](close-x.png "Remove this limiter")
33 matches in the database.
These are records: 1 - 30.
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1.
Bailey, Eric Stanton.
Sparse Frequency Laser Radar Signal Modeling and Doppler Processing.
Degree: MS, Electro-Optics, 2010, University of Dayton
► Sparse frequency, linearly frequency modulated laser radar (ladar) signals achieve improved range…
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▼ Sparse frequency, linearly frequency modulated laser radar (ladar) signals achieve improved range resolution comparable to a larger signal bandwidth. From basic radar/ladar principles it is known that the bandwidth of a signal is inversely proportional to range resolution. Hence, the effective bandwidth of a ladar signal using sparse frequency techniques is larger than the bandwidth of each modulated laser frequency. Previous experiments have validated range resolution and peak to sidelobe ratio derived from models utilizing two segmented bandwidths. This thesis discusses the modeling with three segmented bandwidths. The model is verified against an experimental setup using three frequency offset lasers.The two segmented bandwidth, sparse frequency ladar signal is reexamined to include Doppler effects. The new modeling utilizes a coherent on receive setup allowing for phase information to be processed from the signal. The extracted phase information can be used to determine characteristics about a target, namely its speed and direction with respect to the receiver. This modeling was experimentally verified for cases where the target was next to the receiver, at a distance (simulated through a fiber delay line), and for multiple targets. As a final check of the modeling, the velocity determined from the phase information was compared against the velocity readout of a stage with a built in optical encoder.
Advisors/Committee Members: Powers, Peter.
Subjects: Engineering; Optics; Physics
Keywords: laser radar; ladar; sparse frequency; Doppler; coherent on receive; linear frequency modulation; signal processing
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2.
Berry, Patrick A.
Versatile Chromium-Doped Zinc Selenide Infrared Laser Sources.
Degree: PhD, Electro-Optics, 2010, University of Dayton
► The atmospheric transmission windows of 2-5 and 8-12 µm, coupled with organic…
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▼ The atmospheric transmission windows of 2-5 and 8-12 µm, coupled with organic and other chemical absorption lines occurring throughout this middle-infrared (mid-IR) wavelength region give rise to a wide variety of medical, scientific, commercial and military applications. Communications, remote sensing, IR countermeasures, laser surgery and non-invasive imaging are just a few of the drivers of high-power solid-state mid-IR laser development. These laser sources must be versatile enough to operate in a variety of temporal modes from continuous wave (CW) all the way to ultrashort pulse while still being widely tunable for wavelength agility. All of this is required at ever increasing power output levels while conforming to size, weight and power consumption limitations under harsh operating environmental conditions.Chromium-doped zinc selenide (Cr2+:ZnSe) lasers operating in the 2-3 µm region are excellent candidates to help fill these vital roles. As a transition-metal doped II-VI chalcogenide, Cr2+:ZnSe has a number of positive advantages over existing laser sources. Development and power scaling of these lasers however, has been hampered by thermal issues which have so far limited the ability of these lasers to be applied to systems-level development. This work presents research into the nature and mitigation of these critical thermal issues in development of versatile Cr2+:ZnSe laser sources. Advanced models for thermal and laser performance are developed and used to design optimally configured laser systems. Among other advances for this material, >10 W CW output from a Cr2+:ZnSe oscillator and master-oscillator / power amplifier systems producing multi-watt, widely tunable power levels are demonstrated.
Advisors/Committee Members: Powers, Peter.
Subjects: Optics
Keywords: laser; infrared laser; tunable laser; solid-state laser
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3.
Bobb, Ross Lee.
Doppler Shift Analysis for a Holographic Aperture Ladar System.
Degree: MS, Electro-Optics, 2012, University of Dayton
► Since the invention of the laser, laser radars (ladars) have been investigated…
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▼ Since the invention of the laser, laser radars (ladars) have been investigated following the extensive development path of radar systems. Ladar systems have progressed from simple direct detect systems to more complicated synthetic aperture heterodyne systems. Developments in digital processing allowed a new type of synthetic aperture ladar known as holographic aperture ladar where the heterodyne detection of temporal synthetic aperture ladar was combined with the holographic digital recording methods. Using holographic aperture ladar increases cross-range resolution, but by using a low bandwidth spatial receiver array instead of a high bandwidth point receiver increases the system's Doppler effect vulnerability for each sub-aperture image. The Doppler frequency offsets are due to projected line of sight velocities across the target. In a broadside imaging configuration, one side of the target will appear to be approaching the target while the other appears to be receding. The projected line of sight velocity is zero at the center of the target (normal to the LOS), and has maximum values at the edges of the target field. This produces an approximately linear differential Doppler frequency shift across the target in the dimension of travel. This spatially dependent, sinusoidal signal is temporally integrated over the fixed integration time of the imaging array which maps the sinusoidal signal into a spatial sinc pattern across the target’s image. Since the targets edges have the highest projected velocities, the sinc pattern appears as a loss in target information effectively reducing the field of view. Faster platform velocities and longer integration times produce larger compressions in the field of view. This paper describes the velocity and integration time required to limit the field of view reduction to a selected value. The first null in the cross sectional sinc pattern is assumed to be a good measure for the compression of the field of view. Analytic expressions and numerical simulations are developed for the impact of differential Doppler frequencies and then verified with laboratory experiments. Four integration times were analyzed in this experiment. Since the motion is relative, the target’s velocity varied. The integration times were 0.25 ms, 0.5 ms, 0.75 ms, and 1.0 ms and the velocities varied between 0 and 14 cm/s. The results of this experiment were in good agreement with the theory and simulation and confirm that selection of faster effective integration times is required to limit data loss due to platform motion.
Advisors/Committee Members: Dierking, Matthew P.
Subjects: Optics
Keywords: laser sensing; digital holography; Doppler frequency; motion compensation; spatial heterodyne; sampling theory
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4.
Booso, Benjamin David.
The Growth of Columnar Thin Films and Their Characterization Within the Visible and Near Infrared Spectral Bands.
Degree: MS, Electro-Optics, 2010, University of Dayton
► Seven series of thin films encompassing metallic, dielectric, and semiconductor materials were…
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▼ Seven series of thin films encompassing metallic, dielectric, and semiconductor materials were deposited onto a substrate by means of electron-beam evaporation. Tilting the substrate at an oblique angle relative to the evaporant source causes an atomic shadowing effect to occur at adjacent deposition locations and results in the growth of a columnar morphology. Scanning electron micrographs for each series validate a film structure and porosity that varies with substrate tilt angle. Angle resolved spectroscopic ellipsometry reveals the anisotropic nature of the different series and determines the optical properties utilizing a best model fit calculation. In some instances, the optical properties of the columnar thin film and its bulk material differ significantly.
Advisors/Committee Members: Sarangan, Andrew.
Subjects: Aerospace materials; Automotive materials; Engineering; Materials science; Optics; Physics
Keywords: columnar thin films; electron beam evaporation; oblique angle deposition; spectroscopic ellipsometry; Mueller matrix; index of refraction; extinction coefficient; scanning electron microscope
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5.
Brown, Robert L.
Stretch Processing Of Simultaneous, Segmented Bandwidth Linear Frequency Modulation In Coherent Ladar.
Degree: MS, Electro-Optics, 2011, University of Dayton
► In stretch processing (SP) both the local oscillator (LO) and the transmitted…
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▼ In stretch processing (SP) both the local oscillator (LO) and the transmitted signal are linearly frequency modulated (LFM). A heterodyne detection process is performed using the LO and the received echo signal, which create a detected signal at a single difference-frequency. The frequency is proportional to the distance the received echo signal travels relative to the LO signal, and the range resolution is inversely proportional to the bandwidth making large bandwidth LFM chirps favorable. However, it is difficult to maintain linearity over a lager bandwidth LFM chirp. On the other hand small bandwidth LFM chirps can be easily produced, so the idea of segmenting the transmitted pulse into multiple small non-overlapping frequency LFM chirps was conceived. The extended frequency bandwidth is recovered in post processing. This technique is called multi-frequency stretch processing (MFSP). The procedure outlined is a practical method to achieve greater range resolution using less expensive technology. Another advantage of this technique is the similar modulation noise on each LFM chirp. The multiple signals are processed using an algorithm developed for extracting the additional bandwidth information. The range resolution is related to the time span and bandwidth of the LFM pulses. For n transmitted LFM chirped signals the range resolution is nearly n times longer. Moreover the required detection bandwidth of the echo signal is lower than for other LFM processing systems without a chirped LO signal.
Advisors/Committee Members: Haus, Joseph.
Subjects: Electrical Engineering; Optics; Physics
Keywords: Stretch Process; Pulse Compression; Ladar; Lidar; Laser Radar; Segmented Frequency; Sparse Frequency; Linear Frequency modulation; SF LFM
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6.
Carns, Jennifer.
Semiconductor Optical Amplifier as a Phase Modulator for Short-Pulse Synthetic Aperture Ladar and Vibrometry.
Degree: PhD, Electro-Optics, 2012, University of Dayton
► The use of a saturated Semiconductor Optical Amplifier (SOA) as both a…
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▼ The use of a saturated Semiconductor Optical Amplifier (SOA) as both a phase modulator and an amplifier for long range laser radar applications is explored. As will be discussed, this concept could reduce the hardware necessary to transmit high bandwidth pulses and allow for the transmission of shorter pulses that are less sensitive to the detrimental effects of target motion. After reviewing the concepts governing ranging, vibrometry, and synthetic aperture ladar, the nature of the phase and amplitude modulation from saturating an amplifier with a high peak power Gaussian pulse is explored. The key SOA parameters affecting the modulation of the output pulse are addressed and optimized, and their impact on the ideal pulse response of a laser radar system is explored. Proof of concept laboratory demonstrations using phase modulated pulses to interrogate stationary, vibrating, and translating targets are also presented. The concept of using a saturated SOA to enable short-pulse synthetic aperture ladar and vibrometry is also explored. This research will show that the range resolution of a ladar system can be optimized by saturating a SOA with a carrier lifetime that is one half the FWHM Gaussian input pulse duration, yielding a substantial improvement in range resolution that is highly insensitive to variations in the input pulse duration and energy.
Advisors/Committee Members: Duncan, Bradley D.
Subjects: Electrical Engineering; Optics
Keywords: Semiconductor Optical Amplifier; Self-Phase Modulation; SOA; Laser Radar; Gain Saturation; Ladar
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7.
Cheng, Wen.
Propagation of Vortex Beams through a turbulent atmosphere.
Degree: MS, Electro-Optics, 2009, University of Dayton
► This thesis study and compare the propagation properties of both scalar and…
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▼ This thesis study and compare the propagation properties of both scalar and vector vortex beams through turbulent atmosphere. The irradiance pattern, degree ofpolarization, and scintillation index of radially polarized beam are computed for different propagation distance into an atmosphere with weak and strong turbulence. Corresponding properties of a fundamental Gaussian beam, a scalar vortex beam with topological charge of +1 propagating through an atmosphere under the same turbulence condition are calculated for comparison. The results demonstrate that the existence of the vectorial vortex can be identified with longer propagation distance than the scalar vortex even with disappearing characteristic vortex structure in the irradiance images. This indicates the potential advantages of using vector vortex to mitigate atmospheric effects and enable a more robust free space communication channel with longer link distance.
Advisors/Committee Members: Zhan, Qiwen.
Subjects: Optics
Keywords: Vortex Beam Propagation; Turbulence; Scintillation Index
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8.
CHEN, WEIBIN.
Focus Engineering with Spatially Variant Polarization for Nanometer Scale Applications.
Degree: PhD, Electro-Optics, 2009, University of Dayton
► Spatially variant polarization has stimulated continuous research interests due to its peculiar…
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▼ Spatially variant polarization has stimulated continuous research interests due to its peculiar properties in focusing and surface plasmon excitation, providing broad applications in optical data storage, nano-fabrication, particle trapping, high resolution microscopy and metrology. In this dissertation, focus shaping, three dimensional (3D) state of polarization control, and plasmonic focusing with spatially variant polarization are investigated and demonstrated both theoretically and experimentally. This research shows that 3D flattop focusing with extended depth of focus and optical bubble can be obtained using the combination of generalized cylindrical vector beams and diffractive optical element. Through combining the electric dipole radiation and the Richards-Wolf vectorial diffraction method, the input field at the pupil plane of a high numerical aperture objective lens for generating arbitrary three dimensionally polarization at the focal point with an optimal spot size can be found analytically by solving an inverse problem. In additional to focusing with high numerical aperture lens, spatially variant polarization has great advantage in surface plasmon focusing. Optimal plasmonic focusing can be achieved through matching the polarization symmetry of a radially polarized illumination to axially symmetric dielectric/metal plasmonic lens structures. Three types of plasmonic lens have been studied in this research. Experimental realization of the nondiffracting evanescent Bessel beam generation via surface plamson resonance excitation on homogeneous metallic thin film with radially polarized beam illumination is first demonstrated. Then, plasmonic lens with annular rings under radial polarization illumination is studied. It is found that higher field enhancement factor can be achieved with increasing number of rings in the plasmonic lens. Finally, an apertureless near-field scanning optical microscope probe under radial polarization illumination is numerically studied with 3D finite element method model. The field distribution with a full-width-half-maximum as small as 10 nm and intensity enhancement of five orders of magnitude can be achieved with 632.8 nm optical excitation. Preliminary experimental results using Raman spectroscopy with the designed apertureless tip confirmed the field enhancement through comparing the near field and far field signals.
Advisors/Committee Members: Zhan, Qiwen.
Subjects: Electrical engineering; Electromagnetism; Optics
Keywords: Spatially variant polarization; Cylindrical vector beams; Scanning microscopy, Surface plasmons, Laser beam shaping, Optical confinement and manipulation
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9.
Conrad III, Dallis G.
Speckle Statistics of Articulating Objects.
Degree: MS, Electro-Optics, 2011, University of Dayton
► This thesis documents research to determine if an articulating objects speckle can…
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▼ This thesis documents research to determine if an articulating objects speckle can be used to identify properties of said object. Speckle is an interference phenomenon that is created by coherent light scattering off a rough surface, which creates various path lengths to the observation plane. It was thought that as an object articulates, the average speckle size would vary as time evolved. The average speckle size can be estimated though the speckle field correlation, which is documented to be dependent on two factors: the irradiance distribution of the object, and the correlation properties of the materials composing the target. The irradiance distribution describes the shape and motion of the illuminated object. Its contribution to an object’s speckle pattern was first examined through MATLAB modeling, where those results were tested within laboratory experiments. The understanding of the contribution of the materials composing the object was investigated through recording the speckle pattern of various materials within the lab. The collected speckle irradiance distributions could then be used to determine the correlation properties of that material, which could then be compared to the other materials analyzed.
Advisors/Committee Members: Watson, Edward.
Subjects: Engineering; Optics
Keywords: speckle; speckle field correlation; human modeling; correlation width; correlation coefficient
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10.
Cordray, Jared M.
Investigation of Liquid Crystal Spatial Light Modulators to Simulate Speckle Fields.
Degree: MS, Electro-Optics, 2010, University of Dayton
► We investigate liquid crystal spatial light modulators as a means to simulate…
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▼ We investigate liquid crystal spatial light modulators as a means to simulate the speckle fields produced by laser light scattering off of rough surfaces. Of primary interest was the ability of these devices to accurately simulated the statistical properties of speckle fields. Characterization of the liquid crystal spatial light modulators was performed and a look-up table was created that specified the required voltage for a desired phased on a pixel-by-pixel basis. A model was created to simulate the field leaving the device and the resulting irradiance distribution in the far field. The 2nd and 4th moments of the field at the observation plane were calculated to determine the mean irradiance and contrast of the speckle pattern. Two random phase distributions that create the speckle patterns were investigated. These distributions were uniform phase distribution and "wrapped" Gaussian phase distribution. It was found that the devices are unable to simulate spatially stationary irradiance and contrast. Experimental investigations showed good agreement with the theoretical data except where σ < 0.1π.
Advisors/Committee Members: Watson, Edward.
Subjects: Atmosphere; Optics; Physics
Keywords: liquid crystal; LC; spatial light modulator; SLM; speckle; statistical optics
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11.
Crotty, Maureen.
Signal to Noise Ratio Effects on Aperture Synthesis for Digital Holographic Ladar.
Degree: MS, Electro-Optics, 2012, University of Dayton
► The cross-range resolution of a laser radar (ladar) system can be improved…
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▼ The cross-range resolution of a laser radar (ladar) system can be improved by synthesizing a large aperture from multiple smaller sub-apertures. This aperture synthesis requires a coherent combination of the sub-apertures; that is, the sub-apertures must be properly phased and placed with respect to each other. One method that has been demonstrated in the literature to coherently combine the sub-apertures is to cross-correlate the speckle patterns imaged in overlapping regions. This work investigates the effect of low signal to noise ratio (SNR) on an efficient speckle cross-correlation registration algorithm with sub-pixel accuracy. Specifically, the algorithms ability to estimate relative piston and tilt errors between sub-apertures at low signal levels is modeled and measured. The effects of these errors on image quality are examined using the modulation transfer function (MTF) as a metric. The results demonstrate that in the shot noise limit, with signal levels as low as about 0.02 signal photoelectrons per pixel in a typical CCD, the registration algorithm estimates relative piston and tilt accurately to within 0.1 radians of true piston and 0.1 waves of true tilt. If the sub-apertures are not accurately aligned in the synthetic aperture, then the image quality degrades as the number of sub-apertures increases. The effect on the MTF is similar to the effects due to defocus aberrations.
Advisors/Committee Members: Watson, Edward.
Subjects: Engineering; Optics; Remote Sensing; Scientific Imaging
Keywords: LADAR; Synthetic Aperture Registration; SNR; Speckle Cross-Correlation; MTF; Spatial Heterodyne
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12.
Davis, Antonio A.
Design and Analysis of a Poled-Polymer Electro-Optic Modulator with a Strip-Loaded Waveguide Structure.
Degree: PhD, Electro-Optics, 2010, University of Dayton
► To fully utilize the advances of electro-optic (EO) polymer research, a detail…
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▼ To fully utilize the advances of electro-optic (EO) polymer research, a detail design and model of a triple stacked poled-polymer, electro-optic waveguide modulator was developed to provide guidance in the selection of cladding layers and demonstrate how the mode conditions affect the overall device performance. Waveguide devices depend not only on the EO materials used in the core, but also on the cladding materials. In contrast to most of the research that has focused on molecular engineering of the electro-optically active materials to improve the core properties of the waveguide, this work studied the effects of cladding material properties to improve overall device performance of an electro-optic waveguide modulator. Various, commercially available polymer materials were identified and investigated for potential cladding layers according to their optical, electrical, process ability and film casting properties. A poled-polymer, strip-loaded waveguide, EO modulator is designed and analyzed in terms of single mode conditions, optical loss due to the metal electrodes, modulation efficiency, and mode size. Two designs were compared: Design 1 optimized the half-wave voltage for a single-arm modulator (Vpi = 2.5 V) with a nearly symmetric waveguide by maximizing modulation efficiency and minimizing the overall thickness of the waveguide; Design 2 optimized the insertion loss (6 dB) with a strongly asymmetric waveguide by maximizing the overall mode size to most efficiently overlap with a single mode fiber. High frequency analysis of a microstrip electrode showed a modulator with a push-pull scheme can be fabricated with half-wave voltage (Vpi) of 4.0 V for Design 1 and 5.1 V for Design 2 at 3 GHz. Some general guidelines in the design of a poled-polymer electro-optic modulator incorporating a strip-loaded waveguide structure are suggested. First, the core layer thickness and ridge width supporting single mode propagation should be fabricated as large as possible by increases the asymmetry of the refractive index between the top and bottom cladding layer. Second, the thicknesses of the top and bottom cladding layers must be optimized through an analysis of the waveguide mode amplitude distribution so that the electrode-associated optical loss is minimized to a required level while simultaneously the total thickness of the waveguide is minimized. The ridge structure greatly simplifies fabrication procedures, reduces fabrication steps and eliminates propagation losses due to roughness of etched sidewalls. The results of the analysis were modeled in beam propagation software to confirm the ideal conditions for single mode propagation.
Advisors/Committee Members: Yaney, Perry P.
Subjects: Engineering; Optics; Polymers
Keywords: electro-optic modulator; waveguide design; strip-loaded; poled-polymer; nonlinear chromophore
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13.
Duran, Josh.
Ion Implantation Study of Be in InSb for Photodiode Fabrication.
Degree: MS, Electro-Optics, 2011, University of Dayton
► InSb p-n junction detectors from bulk crystals are commonly utilized for mid-wave…
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▼ InSb p-n junction detectors from bulk crystals are commonly utilized for mid-wave infrared (MWIR) focal-plane arrays (FPAs) because of their high quantum efficiency and well-established fabrication methods. The doping profiles of these detector structures are commonly defined by thermal diffusion techniques because it is an economical and repeatable fabrication process. The resulting impurity profiles have a characteristic shape determined by Fick’s diffusion laws. In order to realize structures that are more complicated than simple PN junctions, like APDs, alternative methods of introducing and controlling impurities need to be developed, especially when high and low doping concentrations at specific depths beneath the surface are needed. Another technique that could maintain similar cost effectiveness and repeatability as thermal diffusion while providing greater control over the doping profile is ion implantation. This is well-developed for silicon, but less developed for InSb. Accurate modeling of the doping profile shapes and depth are important for transitioning detector designs to properly functioning devices. SRIM modeling software is used to predict the doping profiles of implanted Be ions into n-type InSb substrates. To test the accuracy of this software, implantations of varying energy were performed. After implantation, the doping profiles of these samples were measured using secondary ion mass spectrometry (SIMS) before and after a rapid thermal anneal. It was found that Be ions do not diffuse within the repeatability tolerance of the SIMS measurement technique. The SIMS results also revealed a highly oxidized InSb surface. This oxidized surface should be considered during the fabrication process. Spreading resistance profile measurement is made on an annealed Be implanted sample. P on N carrier concentration is verified by this measurement which suggests successful activation during anneal. A process for fabricating InSb photodiodes with ion implantation is developed and reported. The fabrication process has not been optimized for performance, but verification of functioning detectors is established with dark current and spectral response measurements. These measurements verify successful photodiode operation.
Advisors/Committee Members: Sarangan, Andrew.
Subjects: Electrical Engineering; Optics; Physics; Solid State Physics
Keywords: infrared photodetectors; InSb; ion implantation
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14.
Evans, Jonathan W.
Beam Switching of an Nd:YAG Laser Using Domain Engineered Prisms in Magnesium Oxide Doped Congruent Lithium Niobate.
Degree: MS, Electro-Optics, 2010, University of Dayton
► In this work, a novel electro-optic beam switch (EOBS) is designed, fabricated…
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▼ In this work, a novel electro-optic beam switch (EOBS) is designed, fabricated and demonstrated. The EOBS presented in this work is designed for a Nd:YAG laser operating at λ = 1064 nm and is demonstrated to achieve >750 μm of beam translation at switching rates of up to 3 Hz. The EOBS consists of a series of electronically controlled prisms fabricated by ferroelectric domain inversion in an electro-optic crystal wafer. The prisms are arranged such that positive angular deflections are counterbalanced by subsequent negative angular deflections. The result is discrete beam translation with no angular deflection. In this work, an algorithm for designing optimal beam translation geometries is developed. Five of the resulting geometric designs are then fabricated in 5 mol% magnesium oxide doped congruent lithium niobate (5%MgO:CLN). The performance of one particular geometry is modeled in detail and analyzed experimentally. The EOBS is used to demonstrate wavelength tuning of a near-infrared laser system using a selectable optical parametric generation (OPG) grating.
Advisors/Committee Members: Powers, Peter E.
Subjects: Optics
Keywords: Electro-Optic Switching, Beam Steering, Nonlinear Optics, Integrated Optics, Geometric Optics, Electro-Optic Devices
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15.
Feaver, Ryan K.
Longwave-Infrared Optical Parametric Oscillator in Orientation-Patterned Gallium Arsenide.
Degree: MS, Electro-Optics, 2011, University of Dayton
► Coherent tunable laser sources in the longwave infrared (LWIR) spectral region are…
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▼ Coherent tunable laser sources in the longwave infrared (LWIR) spectral region are in high demand for military applications. Most lasers cannot produce outputs far into the infrared region, and therefore a conversion process is needed to achieve desired wavelengths. Quasi-phase matching is a technique that spatially modulates the nonlinear properties of a given material, periodically reversing the induced nonlinear polarization to ensure positive energy flow from the pump source to the converted fields, subject to conservation of energy and momentum. Through the use of optical parametric oscillation (OPO), and nonlinear quasi-phase matched orientation-patterned gallium arsenide (OPGaAs), producing LWIR wavelengths is possible. The OPGaAs OPO was pumped with a Q-switched 2.054μm Tm,Ho:YLF laser. As a precursor to the LWIR OPGaAs OPO, different resonator geometries were explored with a midwave (MWIR) OPGaAs OPO utilizing both SRO and DRO mirror sets. While thresholds increased with cavity length, the slope efficiencies remained relatively similar with the respective mirror set. The LWIR OPGaAs OPO explored the performance using two separate cavity configurations, an SRO and an asymmetric cavity; and five different OPGaAs samples representing three different grating periods. The highest slope efficiency in the SRO LWIR cavity was found to be ~29%, with threshold values of ranging from ~45-90μJ. The slope efficiencies for the asymmetric cavity range from ~4-16% while experiencing higher thresholds of ~150-220μJ, lower overall output power, and increased cavity instability. At higher pump energies, rollover was observed in both cavity configurations. SNLO was used to model the OPO output in the hopes that it might provide some insight into this behavior. The theoretical performance plot fit the acquired data decently but failed to predict the behavior at the higher energies. Spectroscopic data were collected for both OPO signal and idler output, presenting good agreement with theoretical tuning curves.
Advisors/Committee Members: Powers, Peter.
Subjects: Optics
Keywords: Nonlinear optics; Nonlinear optical materials; Parametric processes; Orientation-Patterned Gallium Arsenide
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16.
Finet, Marc A.
Sensor Hardening Through Translation of the Detector from the Focal Plane.
Degree: MS, Electro-Optics, 2012, University of Dayton
► The defense industry has numerous detectors that provide critical imaging capability on…
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▼ The defense industry has numerous detectors that provide critical imaging capability on tactical and reconnaissance platforms and have been shown to be susceptible to permanent damage from high energy pulsed lasers in both laboratory and field testing. Much of the materials research into this involves two different methods of providing pulsed laser damage protection: extrinsic limiter implementation and intrinsic detector hardening. This thesis focused on what gains could be made using another method: system defocus and detector redundancy. The work of this thesis revolved around hardening a camera system through defocusing the focal plane array (FPA) and then using image restoration algorithms to regain the image quality of the degraded images. This system, a three channel image splitting prism with lens mount, provided a unique opportunity to test multiple images of an identical scene with slight spatial misalignments, varying sensor defocus and precisely measured optical degradation as measured by the Point Spread Function. These defocused images were then restored using filters that utilized information from only a single channel (the Wiener Filter, Regularized Least Squares Filter, and Constrained Least Squares Filter) and across multiple channels (Multichannel Constrained Least Squares Filter). Results from the single channel filters were excellent and allowed significant sensor hardening without image degradation when compared to the unfiltered image. Results from the multichannel RLS filter as tested were disappointing when compared to those from the single channel however and could be expanded upon in future work.
Advisors/Committee Members: Hardie, Russell.
Subjects: Acoustics; Electrical Engineering; Optics
Keywords: Image Restoration; multichannel; prism
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17.
Gao, Jian.
Fluorescence Enhancement using One-dimensional Photonic Band Gap Multilayer Structure.
Degree: PhD, Electro-Optics, 2012, University of Dayton
► Fluorescence enhancement using one-dimensional photonic band gap (1DPBG) multilayer structures is demonstrated…
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▼ Fluorescence enhancement using one-dimensional photonic band gap (1DPBG) multilayer structures is demonstrated in this dissertation. Designed with proper refractive indices and thicknesses, the alternating high and low index multilayer thin film structures combine photonic crystal resonance and omni-directional reflection together to enhance the excitation light irradiance and improve the collection efficiency of the fluorescent emission light with different polarizations. Gallium phosphide was chosen as the high index material and its fabrication process was optimized. The field enhancement effect was experimentally confirmed for two designs with achieved enhancement factors of 50~69 folds corresponding to TE and TM waves. The omni-directional reflection effect was measured to be 80% for the incident angles from 5° to 75°. A polarization multiplexed 1DPBG structure was designed with the pixelated terminal layer to enhance both polarizations on the same device. The enhancement factors of 17.9 folds and 15.6 folds were experimentally verified for TE and TM excitations at the same resonant angle. These 1DPBG designs may find wide applications in bio-sensing and imaging.
Advisors/Committee Members: Zhan, Qiwen.
Subjects: Engineering
Keywords: fluorescence enhancement; photonic crystal; photonic band gap; gallium phosphide
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18.
Han, Wei.
Transmissive beam steering through Electrowetting Microprism arrays.
Degree: MS, Electro-Optics, 2009, University of Dayton
► In this study, the electrowetting phenomenon is reviewed and two types of…
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▼ In this study, the electrowetting phenomenon is reviewed and two types of Electrowetting Microprism (EMP) beam steering devices are proposed and theoretically characterized: single-prism and bi-prism EMP arrays. For this thesis, an extended beam propagation method is used and numerical calculations of near-field and far-field intensities are performed for both designs. I investigated both one-dimensional and two-dimensional versions of the EMP arrays and determine the beam steering efficiency for both 1D and 2D cases using an incident Gaussian beam. For the phased arrays the diffraction angles are discrete due to the well known grating effect. The angles between the diffraction peaks can be covered by applying a tilted phase to the input field. The efficiency is measured over continuously changed far-field angles for different situations.
Advisors/Committee Members: Haus, Joseph W.
Subjects: Optics
Keywords: Beam steering; Electrowetting microprism; Far-field diffraction efficiency
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19.
Katte, Nkorni.
Super-resolution and Nonlinear Absorption with Metallodielectric Stacks.
Degree: PhD, Electro-Optics, 2011, University of Dayton
► We investigate sub-wavelength imaging, i.e. super-resolution, in metal-dielectric film systems, which are…
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▼ We investigate sub-wavelength imaging, i.e. super-resolution, in metal-dielectric film systems, which are simply referred to as metallodielectrics. Our simulations incorporate experimentally derived material dielectric dispersion properties across the visible region. For demonstration purposes we designed metallodielectric stacks for super-resolution containing GaP and TiO2, dielectric films, and either Ag or Au as the metallic materials. Using the known optical properties of the constituent materials found designs that could be good candidates for super-resolution. We did not have the resources to fabricate these samples; however, based on our computer simulations we are confident that the designed samples would produce super-resolution approaching one-twentieth of a wavelength in air. We examined for the first time the broad bandwidth of the super-resolution phenomenon in metallodielectrics. We validate the results using the finite element method (FEM) and the transfer matrix method (TMM). We also show that the measurement of super-resolution is highly dependent on the distance of the probe from the exit surface; high resolution at the exit plane can quickly decay with a few tens of nanometers when high resolution is sought. Secondly we numerically studied the nonlinear optical transmission of an optical beam through heterogeneous metallodielectric stacks under the action of nonlinear absorption. One film layer is a metal and the other layer is a dielectric; the heterogeneous material is called a metallodielectric stack (MDS). In these studies we also used applied FEM with two-dimensional transverse effects and TMM simulation techniques. Our samples consisted of Ag/ZnS, Ag/SiO2 and Cu/ZnS. We numerically simulate using two transverse dimensions in our FEM codes, Z-scan experiments for two different MDS designs and draw general observations from these cases. We experimentally examined the nonlinear absorption effect in samples of Ag/SiO2 when irradiated by a femtosecond pulse width beam. There is a significant nonlinear enhancement effect observed in high transmission spectral regimes, which is attributed to field confinement in the metal layers. We showed how the nonlinear absorption varies with wavelength, which changes the field penetration within the stack layers. These results can be applied for of optical limiters and switches.
Advisors/Committee Members: Haus, Joseph.
Subjects: Electromagnetics; Optics
Keywords: Metallodielectric Stacks, Super-resolution, Nonlinear Absorption
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20.
Kraczek, Jeffrey Read.
Piston Phase Measurements to Accelerate Image Reconstruction in Multi-Aperture Systems.
Degree: MS, Electro-Optics, 2011, University of Dayton
► Multi-aperture imaging has been used to receive high resolution images from arrays…
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▼ Multi-aperture imaging has been used to receive high resolution images from arrays of sub-apertures. The use of sub-aperture arrays allows for more compact optical systems and enables conformal aperture imaging. Images collected from these arrays are processed to obtain the high resolution image. A High resolution image is created from an accurate representation of the pupil plane fields in each sub-aperture. Data processing to create an image is time consuming and computationally heavy. Compensating for the unknown piston phase error between the different sub-apertures is one of the more time consuming corrections required to process the image data into a single image. Sub-aperture phasing simulations are used to explore the processing of multi-aperture arrays. The data is processed for several sub-aperture arrays, including 2 and 3 in-line sub-aperture arrays, and hex 7 and 19 sub-aperture arrays. A scheme is proposed for measuring the piston phases in each sub-aperture. It is shown through numerical simulations that a system that measures the piston phase could significantly reduce the processing time required to phase the images from a multi aperture system into a single high resolution image.
Advisors/Committee Members: McManamon, Paaul.
Subjects: Electrical Engineering; Optics
Keywords: coherent laser radar; digital holography; spatial heterodyne; multiple aperture arrays; speckle; image sharpening
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21.
Li, Han.
Transfer Matrix Approach to Propagation of Angular Plane Wave Spectra Through Metamaterial Multilayer Structures.
Degree: MS, Electro-Optics, 2011, University of Dayton
► The development of electromagnetic metamaterials for perfect lensing and optical cloaking has…
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▼ The development of electromagnetic metamaterials for perfect lensing and optical cloaking has given rise to novel multilayer bandgap structures using stacks of positive and negative index materials. Gaussian beam propagation through such structures has been analyzed using transfer matrix method (TMM) with paraxial approximation, and unidirectional and bidirectional beam propagation methods (BPMs). In this thesis, TMM is used to analyze non-paraxial propagation of transverse electric (TE) and transverse magnetic (TM) angular plane wave spectra in 1 transverse dimension through a stack containing layers of positive and negative index materials. The TMM calculations are exact, less computationally demanding than finite element methods, and naturally incorporate bidirectional propagation.
Advisors/Committee Members: Banerjee, Partha.
Subjects: Optics
Keywords: Metamaterials; TMM; Non-paraxial; Bidirectional beam propagation methods
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22.
McDaniel, Sean A.
Seeded, Gain-switched Chromium Doped Zinc Selenide Amplifier.
Degree: MS, Electro-Optics, 2012, University of Dayton
► Many scientific and military applications require pulsed laser sources with high peak…
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▼ Many scientific and military applications require pulsed laser sources with high peak power output which are tunable throughout the midwave infrared (mid-IR) spectral region. In this report we discuss the design, construction, and characterization of a gain-switched chromium-doped zinc selenide (Cr:ZnSe) amplifier pumped by a Q-switched holmium-doped yttrium aluminum garnate (Ho:YAG) laser and seeded by a free running continuous wave (CW) Cr:ZnSe laser. The amplifier pump laser was constructed using a 0.5% Ho-doped, Brewster-cut YAG rod. In CW operation, powers of up to 3.68 W and a slope efficiency of 45% were obtained. In pulsed operation at 1 kHz pulse repetition frequency (PRF), pulse energies of 2.6 mJ per pulse were obtained with temporal pulse widths less than 100 ns. The output wavelength of the pump was 2.1 μm with a spectral width less than 1 nm. The pulsed Ho:YAG laser was then used to gain-switch a Cr:ZnSe single-pass pulsed amplifier seeded with a CW Cr:ZnSe laser with a free-running wavelength of 2.4 μm and a spectral linewidth of 50 nm. The output of the gain-switched amplifier yields a pulsed beam at the seed wavelength demonstrating high gain. By design, this source will follow the lasing wavelength of the seed beam allowing for tunability over the entire emission wavelength of Cr:ZnSe with proper seed design. The end result of this work was a versatile, pulsed mid-IR source.
Advisors/Committee Members: Powers, Peter.
Subjects: Optics
Keywords: Mid-IR laser, Cr:ZnSe, laser
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23.
Phelps, Charles Dustin.
Diode-Pumped, 2-Micron, Q-Switched Tm:YAG Microchip Laser.
Degree: MS, Electro-Optics, 2011, University of Dayton
► In this report we discuss the design, simulation, construction, and characterization of…
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▼ In this report we discuss the design, simulation, construction, and characterization of an actively Q-switched, diode-pumped solid state laser operating at 2 μm. The laser cavity has a “microchip” configuration and uses a 6% thulium-doped YAG crystal as the lasing medium. In continuous wave mode, we achieve output powers of up to 450 mW with a slope efficiency of 9.5%. Using an acousto-optic Q-switch, the laser was run in pulsed mode at an average power of 42 mW and a pulse rate of 1.66 kHz. Pulse duration was approximately 400 ns with a pulse energy of 25 μJ. The center wavelength was 2.019 μm with a linewidth of <0.045 nm. Additionally, a design is presented for replacing the active Q-switch with a chromium-doped zinc selenide crystal acting as a saturable absorber passive Q-switch. Finally, we will propose possible future modifications to the laser system design to improve its performance, ruggedness and compactness, and to broaden its functionality.
Advisors/Committee Members: Powers, Peter.
Subjects: Electrical Engineering; Optics
Keywords: lasers; 2 micron; passive q-switching; tm:yag; microchip lasers
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24.
Reierson, Joseph L.
Analysis of Atmospheric Turbulence Effects on Laser Beam Propagation Using Multi-Wavelength Laser Beacons.
Degree: MS, Electro-Optics, 2011, University of Dayton
► Atmospheric turbulence affects optical systems that operate in various atmospheric conditions. The…
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▼ Atmospheric turbulence affects optical systems that operate in various atmospheric conditions. The characteristics of the optical wave transmitted through atmospheric turbulence can undergo dramatic changes resulting in potential system performance degradation. Knowledge of atmospheric turbulence effects would aid in the development of a wide class of atmospheric-optics systems including laser communication, directed energy, lidar, remote sensing, and active and passive imaging systems. In the classical atmospheric turbulence theory, the refractive index structure parameter is the key parameter known to describe the strength of the atmospheric turbulence and accurate measurement of this parameter represents an important task. The refractive index structure parameter can be difficult to measure, as it is influenced by many factors including path length, time of day, season, and microclimate conditions which cannot be applied universally and may change in a matter of minutes. To further complicate atmospheric turbulence characterization, the key assumptions of classical (Kolmogorov) turbulence theory, such as statistical homogeneity and isotropy of the refractive index random field, are not always satisfied. From this viewpoint, experimental analyses to determine the applicability of the Kolmogorov turbulence theory in different optical wave propagation conditions represent important tasks and can assist in the adequate evaluation of atmospheric turbulence effects on optical system performance and design. In this thesis, the applicability of the classical turbulence theory was verified through simultaneous intensity measurements (pupil- and focal-plane intensity distributions) from multi-wavelength laser beacons over a near-ground, near-horizontal, and seven-kilometer-long propagation path. These measurements allowed independent evaluation of the refractive index structure parameter for two different wavelengths (λ1 = 532 nm, λ2 = 1064 nm), and these results were compared to theoretical predictions. In addition, the turbulence-induced intensity scintillations were investigated across the projected laser beam footprint, and a numerical analysis of the propagation was compared to the experimental data. To obtain the intensity measurements, the optical setup included four sub-systems using fast-framing (~150 frames/second) cameras that were synchronized using previously developed control software; additional software was developed for data acquisition and processing. The conducted experiments in the turbulence conditions investigated here showed that the results of measurements and predictions based on the Kolmogorov turbulence theory are in reasonably good agreement but are particularly sensitive to the footprint position of the transmitted beacon. The atmospheric characterization technique using a multi-wavelength beacon provided a useful tool for examining the applicability of the Kolmogorov turbulence theory along this propagation path.
Advisors/Committee Members: Vorontsov, Mikhail A.
Subjects: Engineering; Optics; Physics
Keywords: atmospheric optical turbulence; scintillations; multi-wavelength sensing; optical sensing; remote sensing; imaging through turbulence; laser beam propagation
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25.
Serushema, Jean Bosco.
WAVE PROPAGATION THROUGH MULTI-LAYER METALLO-DIELECTRICS: APPLICATION TO SUPER-RESOLUTION.
Degree: MS, Electro-Optics, 2010, University of Dayton
► In this study, wave propagation through metallo-dielectric (MD) films is studied using…
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▼ In this study, wave propagation through metallo-dielectric (MD) films is studied using an extension of the transfer matrix method. A beam with transverse structure is simulated using a superposition of plane waves. Gaussian beams are examined as incident waves on MD structures. The first part of this thesis is devoted to plane wave propagation through MD structures. Different optical and physical phenomena are systematically calculated, analyzed and discussed, including the transmission and reflection coefficients, and the group index, for three different MD structures by varying parameters such as the metal and dielectric film thicknesses, and the wavelength. The materials used in the design include silver, gold and copper as metals, and gallium phosphate, titanium oxide and silica as dielectrics. For the second part of the thesis, both 1D and 2D Gaussian beam propagation through MD structures are studied with a subset of the materials from the first part. The Gaussian quadrature method is used for Fourier transforming the Gaussian beam profile. The far-field and near-field output intensity profiles for s and p polarization are also calculated for different designs, and candidates for super-resolution are identified. The model is not an exact solution of the physical beam propagation problem, since the super-resolved Gaussian beam is imposed at the input face. However, the results identify potential candidates for super-resolution, and our inferences are in agreement with published results showing super-resolution.
Advisors/Committee Members: Haus, Joseph W.
Keywords: WAVE PROPAGATION THROUGH MULTI-LAYER: APPLICATION TO SUPER-RESOLUTION
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26.
Venable, Samuel Martin III.
Demonstrated Resolution Enhancement Capability of a Stripmap Holographic Aperture Ladar System.
Degree: MS, Electro-Optics, 2012, University of Dayton
► Holographic aperture ladar (HAL) is a variant of synthetic aperture ladar (SAL).…
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▼ Holographic aperture ladar (HAL) is a variant of synthetic aperture ladar (SAL). The two processes are related in that they both seek to increase cross-range (i.e., the direction of the receiver translation) image resolution through the synthesis of a large effective aperture – which is in turn achieved via the translation of a receiver aperture and the subsequent coherent phasing and correlation of multiple received signals. However, while SAL imaging incorporates a translating point detector, HAL takes advantage of two-dimensional translating sensor arrays. For the research presented in this article, a side looking Stripmap HAL geometry was used to sequentially illuminate a set of Ronchi ruling targets. Prior to this, theoretical calculations were performed to determine the baseline, single sub-aperture resolution of our experimental, laboratory based system. Theoretical calculations were also performed to determine the ideal modulation transfer function (MTF) and expected cross-range HAL image sharpening ratio corresponding to the geometry of our apparatus. To verify our expectations, we first sequentially captured an over-sampled collection of pupil plane field segments for each Ronchi ruling. A HAL processing algorithm was then employed to phase correct and re-position the field segments after which they were properly aligned through a speckle field registration process. Relative piston and tilt phase errors were then removed prior to final synthetic image formation. By then taking the Fourier transform of the synthetic image intensity and examining the fundamental spatial frequency content, we were able to produce experimental modulation transfer function curves which we could then compare to our theoretical expectations. Our results show that we are able to achieve nearly diffraction limited results for image sharpening ratios as high as 6.43
Advisors/Committee Members: Duncan, Brad.
Subjects: Optics
Keywords: Holographic Aperture Ladar; Lidar; Optical Sensing and Sensors; Synthetic Aperture Radar
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27.
Voratovic, Dayen Chad.
Generation and Detection of Coherent Pulse Trains in Periodically Poled Lithium Niobate Through Optical Parametric Amplification.
Degree: MS, Electro-Optics, 2011, University of Dayton
► This work reports on the generation, modulation, and detection of temporally coherent…
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▼ This work reports on the generation, modulation, and detection of temporally coherent pulses in periodically-poled lithium niobate (PPLN) configured as an optical parametric amplifier (OPA). The OPA was pumped at 1 µm, by a 10 kHz, 1 ns, Nd:YAG laser. The cw seeding sources for the OPA were two separate 1550 nm lasers. One source had a short coherence length of .3 km, the other a long coherence length of 95 km. The generated pulse trains where phase modulated by using a set of mirrors on a single axis motorized stage. A 10 km fiber optic delay line was used to simulate free space propagation. A homodyne, coherent optical detection system, utilizing the in-phase and quadrature components of the circularly polarized local oscillator, was built to detect the amplitude and phase modulated pulse trains. We report the detection of the modulated signal for the long coherence length source and the loss of the modulated signal for the short coherence length source, demonstrating that the OPA process can transfer the temporal coherence (or coherence length) of the input signal to the pulse-amplified signal
Advisors/Committee Members: Powers, Peter.
Subjects: Engineering
Keywords: ppln; coherent detection; coherence length; optical parametric amplifier; pulsed laser
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28.
Wan, Chenchen.
Optical Tweezers Using Cylindrical Vector Beams.
Degree: MS, Electro-Optics, 2012, University of Dayton
► Optical trapping by a highly focused laser beam has been extensively used…
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▼ Optical trapping by a highly focused laser beam has been extensively used for the manipulation of submicron-size particles and biological structures. Usually the gradient force will support a stable trapping while the scattering force will push the particles away and destroy the stable trapping. Metallic particles are generally considered difficult to trap due to strong scattering and absorption forces. As one class of spatially variant polarized beams, cylindrical vector beam (CV beam) is proven to have advantage for metallic particle trapping because the axial scattering force is identical zero. In this work, CV beam is generated and applied to trap metallic nanoparticles while the expected stable trapping is not observed. Several possible reasons are examined and the argument that a curl scattering force is responsible for the trapping difficulty is proposed. The curl scattering force is usually neglected in previous research for linearly polarized beam trapping. Numerical simulation shows the curl scattering force can be significant when vectorial beams such as CV beams are used for trapping. After realizing the significance of the curl force, innovative methods to engineer the forces are proposed and investigated to find the fields distribution which could support three dimensional stable trapping.
Advisors/Committee Members: Zhan, Qiwen.
Subjects: Optics
Keywords: Optical tweezers; trapping; cylindrical vector beams; radial polarization; golden nanoparticle; optical force; curl scattering force; focus shaping
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29.
Wang, Long.
Talbot Imaging in Multi-mode Optical Fibers with Periodic Multiple Sub-apertures.
Degree: MS, Electro-Optics, 2011, University of Dayton
► In this thesis the operation of an all-optical, fiber-based, compact, phase-locked multi-fiber…
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▼ In this thesis the operation of an all-optical, fiber-based, compact, phase-locked multi-fiber laser design is explored using the Talbot self-imaging effect. We use the beam propagation method to simulate diffraction and refraction of light in the Talbot mirror fiber device (TMFD), which is a cylindrically shaped waveguide. The details of the device are described and its optical properties using a close-packed hexagonally-shaped array of apertures placed at regular positions on a triangular lattice are examined in this thesis. We numerically analyze the propagation, diffraction and coupling characteristics of the beam oscillating inside the TMFD. Our simulations identify the optimal length of the large mode area fiber (LMA fiber) to get high fidelity in the self-image. Experiments are performed to validate the simulation results.
Advisors/Committee Members: Haus, Joseph W.
Subjects: Optics
Keywords: Talbot imaging; phase-locked; fiber laser
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30.
Wu, Guimin.
Wavefront Control With Realistic Spatial Light Modulator in a Multi-aperture Imager.
Degree: MS, Electro-Optics, 2012, University of Dayton
► A multi-aperture imaging system with a non-mechanical steering device replacing each lens…
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▼ A multi-aperture imaging system with a non-mechanical steering device replacing each lens sub-aperture was considered. This setup allows for focusing and tracking of a target over a fine angle while preserving high resolution imaging in a compact system. An imaging system has the ability to digitally add focus for receiving. However, in the case of transmitting the focus must be provided by optical components. Even when receiving, at a short enough range it might be necessary to introduce optical corrections to avoid phase aliasing. To this end, the effects of implementing a real device such as the BNS Spatial Light Modulator (SLM), a reflective 512x512 pixels with 83.4% area fill factor steering device, on the multi aperture imaging system were investigated. The pixelated phase of the SLM, and the use of 2π resets to provide stepped blazed phase profiles for steering and stepped quadratic phase focusing, are modeled. Each pixel of the SLM is modeled by an array of 10x10 elements with 9 active and 1 inactive in both the x and y direction. As expected, and shown by the simulation results, the periodic reset of the quadratic phase bowl introduced phase grating modulations, which produces the so call “ghost image” around the center image. By only providing stepped blazed profile to steer, the simulation shows that with increasing phase steps within the blazed profile the diffraction efficiency increase but at the cost of decreased steering angles. The ability of the SLM to correct for aberrations and its limitation in correcting aberration is investigated. Further, the basic concept of conformal aperture, enabled by the multi-aperture, was investigated and simulated.
Advisors/Committee Members: McManamon, Paul F.
Subjects: Optics
Keywords: Wavefront control; SLM; multi-aperture imaging; beam steering; conformal aperture
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