Optics Commons^™

Midwave Infrared Imaging Fourier Transform Spectrometry Of Combustion Plumes, Kenneth C. Bradley

Theses and Dissertations

A midwave infrared (MWIR) imaging Fourier transform spectrometer (IFTS) was used to successfully capture and analyze hyperspectral imagery of combustion plumes. Jet engine exhaust data from a small turbojet engine burning diesel fuel at a flow rate of 300 cm³/min was collected at 1 cm⁻¹ resolution from a side-plume vantage point on a 200x64 pixel window at a range of 11.2 meters. Spectral features of water, CO, and CO² were present, and showed spatial variability within the plume structure. An array of thermocouple probes was positioned within the plume to aid in temperature analysis. A single-temperature …

Light Beaming From A Single Subwavelength Metal Slit, Pengyu Chen

All Theses

In this thesis, light transmission through a single sub-wavelength slit in a silver thin film with periodic gratings at the exit side of the slit has been studied in both the visible and mid-infrared wavelength ranges.
In the visible wavelength range, we first investigate the enhancement of plasmonic light beaming efficiency by near field resonance in a subwavelength metallic slit-groove beaming structure. We show that by varying the film thickness and the separation distance of the beaming grating, the intensity of the near field can be greatly enhanced by resonance, which leads to the increase of the beaming efficiency. Moreover, …

Comparison Of Line-Peak And Line-Scanning Excitation In Two-Color Laser-Induced-Fluorescence Thermometry Of Oh, Stanislav Kostka, Sukesh Roy, Patrick J. Lakusta, Terrence Meyer, Michael W. Renfro, James R. Gord, Richard D. Branam

Faculty Publications

Two-line laser-induced-fluorescence (LIF) thermometry is commonly employed to generate instantaneous planar maps of temperature in unsteady flames. The use of line scanning to extract the ratio of integrated intensities is less common because it precludes instantaneous measurements. Recent advances in the energy output of high-speed, ultraviolet, optical parameter oscillators have made possible the rapid scanning of molecular rovibrational transitions and, hence, the potential to extract information on gas-phase temperatures. In the current study, two-line OH LIF thermometry is performed in a well-calibrated reacting flow for the purpose of comparing the relative accuracy of various line-pair selections from the literature and …

Comparing Experts And Novices In Solving Electrical Circuit Problems With The Help Of Eye-Tracking, David Rosengrant, Colin Thomson, Taha Mzoughi

Faculty Articles

In order to help introductory physics students understand and learn to solve problems with circuits, we must first understand how they differ from experts. This preliminary study focuses on problem-solving dealing with electrical circuits. We investigate difficulties novices have with circuits and compare their work with those of experts. We incorporate the use of an eye-tracker to investigate any possible differences or similarities on how experts and novices solve electrical circuit problems. Our results show similarities in gaze patterns among all subjects on the components of the circuit. We further found that experts would look back at the circuit while …

How Much Can Guided Modes Enhance Absorption In Thin Solar Cells?, Peter N. Saeta, Vivian E. Ferry, Domenico Pacifici, Jeremy N. Munday, Harry A. Atwater

All HMC Faculty Publications and Research

Absorption enhancement in thin metal-backed solar cells caused by dipole scatterers embedded in the absorbing layer is studied using a semi-analytical approach. The method accounts for changes in the radiation rate produced by layers above and below the dipole, and treats incoherently the subsequent scattering of light in guided modes from other dipoles. We find large absorption enhancements for strongly coupled dipoles, exceeding the ergodic limit in some configurations involving lossless dipoles. An antireflection-coated 100-nm layer of a-Si:H on Ag absorbs up to 87% of incident above-gap light. Thin layers of both strong and weak absorbers show similar strongly enhanced …

Continuous Phase Amplification With A Sagnac Interferometer, David J. Starling, P. Ben Dixon, Nathan S. Williams, Andrew N. Jordan, John C. Howell

Mathematics, Physics, and Computer Science Faculty Articles and Research

We describe a phase-amplification technique using a Sagnac interferometer. We monitor the relative phase between two paths of a precisely misaligned interferometer by measuring the average position of a split-Gaussian mode in the dark port. Although we monitor only the dark port, we show that the signal varies linearly with phase and that we can obtain similar sensitivity to balanced homodyne detection. We derive the source of the amplification using classical wave optics.

Ultrafast Gain And Refractive Index Dynamics In Gainnassb Semiconductor Optical Amplifiers, Tomasz Piwonski, J. Pulka, Gillian Madden, Guillaume Huyet, John Houlihan

Cappa Publications

The gain and refractive index dynamics of dilute nitride antimonide semiconductor optical amplifiers are studied using heterodyne pump probe spectroscopy, both in forward and reverse bias regimes. In the forward biased absorption regime, both gain and refractive index relax on the same timescale indicating that both quantities are linked to the same relaxation process, interband recombination. Above transparency, in the forward biased gain regime, the gain and phase exhibit differing timescales resulting in a dynamical alpha factor that varies strongly with time. Reversed bias measurements suggest a recombination dominated absorption recovery where the recovery timescale increases with increasing reversed bias, …

Optimizing The Signal-To-Noise Ratio Of A Beam-Deflection Measurement With Interferometric Weak Values, David J. Starling, P. Ben Dixon, Andrew N. Jordan, John C. Howell

Mathematics, Physics, and Computer Science Faculty Articles and Research

The amplification obtained using weak values is quantified through a detailed investigation of the signal-to-noise ratio for an optical beam-deflection measurement. We show that for a given deflection, input power and beam radius, the use of interferometric weak values allows one to obtain the optimum signal-to-noise ratio using a coherent beam. This method has the advantage of reduced technical noise and allows for the use of detectors with a low saturation intensity. We report on an experiment which improves the signal-to-noise ratio for a beam-deflection measurement by a factor of 54 when compared to a measurement using the same beam …

Image Registration Using Conformal Log Polar Mapping, Bala Krishna Vadapally

Electrical & Computer Engineering Theses & Dissertations

Image Registration is the process of aligning, or overlaying two images of the same scene that were taken at different times and/or from different viewing angles and/or by sensors with different modalities or resolutions. The variations in the imaging environment induce the difference between the images of the same scene. In our situation, we have two images of the same scene taken with two sensors, one in the visible and the other in the infrared (IR) domain. The cameras are placed adjacent to each other on a stable platform, and the images are captured almost simultaneously. This means that the …

Photopolymers: Beyond The Standard Approach To Photosensitisation, Izabela Naydenova, Suzanne Martin, Vincent Toal

Articles

A photopolymerizable material for use in the visible normally consists of a dye sensitizer, a free radical generator, monomer/monomers and, optionally, a binder, and is prepared usually as a dry or liquid film. Upon illumination with light of appropriate wavelength, a photopolymerisation reaction is triggered, leading to a change in the film’s refractive index. Because the presence of the dye is essential, the film is usually made sensitive to light during its preparation. Here we separate the film preparation and the sensitisation processes. In this way the photopolymerisation process can be used to detect dye labelled analytes, providing an alternative …

Anomaly Detection In Hyperspectral Imagery: Comparison Of Methods Using Diurnal And Seasonal Data, Patrick C. Hytla, Russell C. Hardie, Michael T. Eismann, Joseph Meola

Electrical and Computer Engineering Faculty Publications

The use of hyperspectral imaging is a fast growing field with many applications in the civilian, commercial and military sectors. Hyperspectral images are typically composed of many spectral bands in the visible and infrared regions of the electromagnetic spectrum and have the potential to deliver a great deal of information about a remotely sensed scene. One area of interest regarding hyperspectral images is anomaly detection, or the ability to find spectral outliers within a complex background in a scene with no a priori information about the scene or its specific contents. Anomaly detectors typically operate by creating a statistical background …

Scene-Based Nonuniformity Correction With Reduced Ghosting Using A Gated Lms Algorithm, Russell C. Hardie, Frank Orion Baxley, Brandon J. Brys, Patrick C. Hytla

Electrical and Computer Engineering Faculty Publications

In this paper, we present a scene-based nouniformity correction (NUC) method using a modified adaptive least mean square (LMS) algorithm with a novel gating operation on the updates. The gating is designed to significantly reduce ghosting artifacts produced by many scene-based NUC algorithms by halting updates when temporal variation is lacking. We define the algorithm and present a number of experimental results to demonstrate the efficacy of the proposed method in comparison to several previously published methods including other LMS and constant statistics based methods. The experimental results include simulated imagery and a real infrared image sequence. We show that …

Design Of Acousto-Optic Chaos Based Secure Free-Space Optical Communication Links, Anjan K. Ghosh, Pramode K. Verma, Samuel Cheng, Robert C. Huck, Monish Ranjan Chatterjee, Mohammed A. Al-Saedi

Electrical and Computer Engineering Faculty Publications

We discuss the design of an acousto-optic cell based free space optical communication link where the data beam is made secure through chaos encryption. Using external signal modulation of the diffracted light from a hybrid acousto-optic cell chaos (or directly via incorporation in the sound-cell driver's bias voltage) encryption of data is possible. We have shown numerically that decryption of the encoded data is possible by using an identical acousto-optic system in the receiver.

Compensation Of Loss And Stimulated Emission Of Surface Plasmon Polaritons, Guohua Zhu

Electrical & Computer Engineering Theses & Dissertations

Surface plasmon polaritons (SPPs) have become in recent years an important research topic because of their interesting, physics and exciting potential applications, ranging from sensing and biomedicine to nanoscopic imaging and information technology. However, many applications of surface plasmon polaritons are hindered by one common cause—absorption loss in metal.

Over the years, numerous proposals have been made on how to conquer the plasmon loss. In this dissertation, (1) the known solutions to the loss problem by adding optical gain have been reviewed; (2) the properties of surface plasmon polaritons are studied theoretically, and the solution of the controversy regarding the …

Characterisation Of The Humidity And Temperature Responses Of A Reflection Hologram Recorded In Acrylamide-Based Photopolymer, Izabela Naydenova, Raghavendra Jallapuram, Vincent Toal, Suzanne Martin

Articles

The humidity and temperature responses of a reflection hologram recorded in a self-processing photopolymer layer have been characterised by measurement of the position of the maximum intensity in the spectral response of the hologram. It has been demonstrated that such a hologram can be used for indication of the relative humidity (RH) in a specific temperature range. The operational range and reversibility of the holograms have been characterised in a controlled humidity and temperature environment. The humidity studies were carried out in the range from 10 to 80% RH and the temperature range under study was 15 – 50 ºC.

Imaging Second-Harmonic Radiation And Scattering Patterns In Zno Micro/Nanostructures, Katrina Marie Geren

Graduate Theses and Dissertations

The optical characteristics of ZnO nanostructures have recently garnered interest due to the inclusion of these structures in many nanoscale optical and optoelectronic devices. This thesis will address several characteristics involving second harmonic generation and scattering in ZnO nano- and microstructures. A method will be presented for determining the nonlinear coefficients of the second order susceptibility in a single ZnO rod. This method uses transmission geometry where previous methods have employed back-reflected irradiation. The nonlinear coefficients found using this new technique were consistent with previous data from similar structures. Models will be presented for predicting the second harmonic scattering patterns …

Ultrasensitive Beam Deflection Measurement Via Interferometric Weak Value Amplification, P. Ben Dixon, David J. Starling, Andrew N. Jordan, John C. Howell

Mathematics, Physics, and Computer Science Faculty Articles and Research

We report on the use of an interferometric weak value technique to amplify very small transverse deflections of an optical beam. By entangling the beam’s transverse degrees of freedom with the which-path states of a Sagnac interferometer, it is possible to realize an optical amplifier for polarization independent deflections. The theory for the interferometric weak value amplification method is presented along with the experimental results, which are in good agreement. Of particular interest, we measured the angular deflection of a mirror down to 400

All Optical Waveguiding In A Coherent Atomic Rubidium Vapor, Praveen K. Vudyasetu, David J. Starling, John C. Howell

Mathematics, Physics, and Computer Science Faculty Articles and Research

We demonstrate an all optical waveguide imprinted by a low power Laguerre Gaussian control laser beam using a coherent Raman process in warm atomic rubidium vapor. We show that the signal beam propagates with a small spot size over several diffraction lengths. We also show that the coupling efficiency of the signal beam into the waveguide varies linearly with the signal power.

Investigation Of Electrical And Optical Properties Of Bulk Iii-V Ternary Semiconductors, Travis C. Gomez

Theses and Dissertations

Bulk grown III-V ternary semiconductors of In_0.08Ga_0.92Sb and In_0.15Ga_0.85As were investigated through Hall-effect and photoluminescence measurements to determine carrier concentration, mobility, sheet resistivity, and luminescence spectrum. In the past, epitaxial layers of ternary compounds have been grown on binary compound substrates, and thus very limited lattice matched ternary alloys were available. Recently, bulk grown ternary substrates have been developed, and it has presented a renewed interest in using these substrates to grow high quality ternary compounds for use in many next generation optoelectronic devices. The results of photoluminescence (PL) study for the …

A Comparative Study Of The Bidirectional Reflectance Distribution Function Of Several Surfaces As A Mid-Wave Infrared Diffuse Reflectance Standard, Bradley Balling

Theses and Dissertations

The Bi-Directional Reflectance Distribution Function (BRDF) has a well defined diffuse measurement standard in the ultraviolet, visible, and near infrared (NIR), Spectralon(trade name). It is predictable, stable, repeatable, and has low surface variation because it is a bulk scatterer. In the mid-wave IR (MWIR) and long-wave IR (LWIR), there is not such a well-defined standard. There are well-defined directional hemispherical reflectance (DHR) standards, but the process of integrating BRDF measurements into DHR for the purpose of calibration is problematic, at best. Direct BRDF measurement standards are needed. This study use current calibration techniques to ensure valid measurements and then systematically …

A Computational Tool For Evaluating Thz Imaging Performance In Brownout Conditions At Land Sites Throughout The World, Seth L. Marek

Theses and Dissertations

This study quantifies terahertz (THz) or sub-millimeter imaging performance during simulated rotary-wing brownout or whiteout environments based on geographic location and recent/current atmospheric weather conditions. The atmospheric conditions are defined through the Air Force Institute of Technology Center for Directed Energy (AFIT/CDE) Laser Environmental Effects Definition and Reference or LEEDR model. This model enables the creation of vertical profiles of temperature, pressure, water vapor content, optical turbulence, and atmospheric particulates and hydrometeors as they relate to line-by-line layer extinction coefficient magnitude at wavelengths from the UV to the RF. Optical properties and realistic particle size distributions for the brownout and …

Theoretical Model Analysis Of Absorption Of A Three Level Diode Pumped Alkali Laser, Charlton D. Lewis Ii

Theses and Dissertations

This paper models the absorption phenomena of light in a three level diode pumped alkali laser system. Specifically this model calculates for a user defined set of system parameters the attenuation of the input pump beam and characteristics of the bleached wave. Using Wolfram's Mathematical 6.0 software all necessary physics for an accurate description of absorption was modeled from first principles: energy levels, cross sections, spin-orbit kinetic processes, saturation frequencies, pump attenuation, and differential transmittance, which is a representation of the bleached wave. A specific DPAL scenario was simulated, 455K system temperature, alkali concentration of 6.1 - 10¹³, …

Analysis And Application Of The Bi-Directional Scatter Distribution Function Of Photonic Crystals, Robert B. Lamott

Theses and Dissertations

Photonic crystals (PCs) are periodic structures built from materials with different refractive indices repeated at sub-wavelength intervals, which results in unusual optical characteristics, including narrowband laser protection, and zero reflectance and high absorption anomalies. Most of the research into the optical properties of PCs has concentrated only on the small range of wavelengths and angles where these effects occur. To better understand where all light leaving a PC is scattered, a Complete Angle Scatter Instrument was used to analyze the scatter from three Guided Mode Resonance Filters designed for laser protection. In the plane of incidence, measurements of the scatter …

Wave Optics Simulation Of Optically Augmented Retroreflections For Monostatic/Bistatic Detection, John J. Tatar Iii

Theses and Dissertations

Optical devices interrogated with a laser in the appropriate band can exhibit strong, deterministic reflections of the incident beam. This characteristic could be exploited for optical target detection and identification. The distribution of reflected power is strongly dependent on the geometry of the interrogation scenario, atmospheric conditions, and the cross section of the target optical device. Previous work on laser interrogation systems in this area has focused on analytic models or testing. To the best of my knowledge, I am presenting for the first time an approach to predict reflected power for a variety of interrogation configurations, targets, and propagation …

Misregistration In Adaptive Optics Systems, Nathan D. Engstrom

Theses and Dissertations

An adaptive optics (AO) system is most effective when there is a known alignment between the wave front sensor (WFS) and the deformable mirror (DM). Misregistration is the term for the unknown alignment between the WFS and DM. Misregistration degrades system performance and can make the system unstable. An AO system uses a reconstruction matrix to transform WFS measurements into DM commands. A standard AO system uses a model reconstruction matrix that assumes perfect registration between the WFS and DM. The object of this research is to mitigate the negative effects of misregistration by using offline WFS measurements to create …

Evaluation Of Performance Of A Maximum Likelihood Estimator For Tracking Purposes In The Presence Of Speckle Noise, Adrian Brett Monz

Theses and Dissertations

In many cases, optical tracking systems do not have cooperative beacons avail- able. This is particularly true for the case involving tracking a laser illuminated target such as a missile seeker head, where the object of interest is an extended source. Furthermore the extended source is often observed in the presence of noise such as shot and speckle noise as well as atmospheric turbulence which further degrades the signal. This research effort presents the evaluation of an existing algorithm based on the maximum-likelihood technique for tilt estimation in the presence of extended sources and speckle noise, with particular application to …

Adaptive Control Of Woofer-Tweeter Adaptive Optics, Jimmie J. Perez

Theses and Dissertations

Adaptive optics applies advanced sensing and control to improve the ability of optical systems to collect images through a turbulent atmosphere. The results of this research effort demonstrate that the combination of two recent approaches improves the performance of adaptive optics in directed energy and laser communication scenarios. The first approach is adaptive control, which offers improved performance over fixed-gain controllers in the presence of rapidly changing turbulence. The second approach incorporated into the study is a dual-mirror system. The two mirrors are a high-bandwidth, low-actuator-stroke (tweeter) mirror and a low-bandwidth, large actuator-stroke (woofer) mirror. The woofer-tweeter combination allows for …

Tilted Parallel Dielectric Slab As A Multilevel Attenuator For Incident P- Or S-Polarized Light, R. M.A. Azzam

Electrical Engineering Faculty Publications

Under the condition of first-order blooming, a parallel dielectric slab, which is inserted in the path of an obliquely incident p- or s-polarized light beam, introduces multiple discrete attenuation levels given by 1/3, 4/27, 4/243,...... in reflection and 4/9, 4/81, 4/729,...... in transmission. These attenuation levels are independent of the slab refractive index, incident p or s linear polarization, or the presence of identical transparent surface coatings at the front and back sides of the slab. Therefore, the tilted slab provides multidecade reflectance and attenuation reference values that can be used in calibrating spectrophotometers and filters, and also …

Realization Of An All-Optical Zero To Cross-Phase Modulation Jump, Ryan M. Camacho, P. Ben Dixon, Ryan T. Glasser, Andrew N. Jordan, John C. Howell

Mathematics, Physics, and Computer Science Faculty Articles and Research

We report on the experimental demonstration of an all-optical π cross-phase modulation jump. By performing a preselection, an optically induced unitary transformation, and then a postselection on the polarization degree of freedom, the phase of the output beam acquires either a zero or π phase shift (with no other possible values). The postselection results in optical loss in the output beam. An input state may be chosen near the resulting phase singularity, yielding a π phase shift even for weak interaction strengths. The scheme is experimentally demonstrated using a coherently prepared dark state in a warm atomic cesium vapor.

Power Scaling Of Large Mode Area Thulium Fiber Lasers In Various Spectral And Temporal Regimes, Timothy Mccomb

Electronic Theses and Dissertations

High power thulium fiber lasers are interesting for a myriad of applications due to their potential for high average output power, excellent beam quality, compactness, portability, high operating efficiency and broad, eye-safe spectral range from 1.8-2.1 microns. Currently, the majority of thulium laser research effort is being invested into scaling average output powers; however, such output powers are being scaled with no degree of control on laser system output spectrum or temporal behavior. Thulium fiber laser technology is not useful for many of its most important applications without implementation of techniques enabling tunable, narrow spectral widths with appropriate pulse durations …