Engineering Commons^™

Dynamic Behavior Of Co₂ Lasers, Li Zhang

Dissertations and Theses

Spontaneous pulsations have been observed in the output of a CO₂ laser. The temporal waveforms, transverse mode patterns, and laser lines are simultaneously measured under various operation conditions. The experimental data show that these pulsations have a direct connection with the transverse modes. We interpret the oscillations as being caused by mode beating, and the frequency shift of the oscillation as resulting from mode pulling. The theoretical explanations for these effects are in good agreement with the experimental results.

Endless State-Of-Polarization Control For Coherent Optical Communication Systems Using Nematic Liquid Crystal, Scott H. Rumbaugh

Dissertations and Theses

One of the obstacles to coherent fiber-optic communications is the unpredictable polarization drift which necessitates the use of an active polarization controlling system to match the polarizations of the signal and local oscillator. The polarization match must be maintained during the reset of any of the finite range components to prevent loss of data. We present a novel and practical system which uses three liquid crystal devices for the polarization matching process. Also, the required reset control algorithm and its derivation are described in detail.

An Approach To Pattern Recognition Of Multifont Printed Alphabet Using Conceptual Graph Theory And Neural Networks, Ihab A. Harb

Dissertations and Theses

This thesis describes an approach for accomplishing a pattern recognition task using conceptual graph theory and neural networks (NNs). The set of patterns to be recognized are the capital letters of six different fonts of the English alphabet, plus two shifted and six rotated versions of each. The letters are represented to the neural network on a 16x16 input grid (256 "sensor lines"). A standard classification encoding for such patterns is to use a 26-bit vector (26 lines at the NN's output), one bit corresponding to each letter. Experiments with such an encoding yielded results with poor generalization capability. A …

Spontaneous Mode Locking In Long-Cavity Xenon Lasers, Manuela Fe Tarroja, Mohammad Sharafi, Lee W. Casperson

Electrical and Computer Engineering Faculty Publications and Presentations

Spontaneous mode locking in Fabry—Perot xenon lasers has been experimentally investigated for cavity lengths up to 66 m. Our results show dependence of the number of pulses per round-trip time on the cavity length and the excitation current. Other dynamical effects such as the ringing and modulation of the mode-locked pulses have been observed. A semiclassical model for the self-locking of an inhomogeneously broadened laser is also presented. Numerical results based on this model describe many dynamical features observed in our experiments.

A Comparative Study Of The Performance Of Various Image Analysis Methods For Dimensional Inspection With Vision Systems, Ralf Heinrich Koeppe

Dissertations and Theses

Dimensional inspection with Vision Systems requires a careful selection of image analysis methods in order to obtain accurate information about the geometry of the parts to be measured.

The purpose of this project is to study, implement and compare different image evaluation methods and to show their strengths and weaknesses with respect to dimensional inspection. Emphasis is made on the inspection of circular features. The criteria of comparison for these methods are discussed. Using synthetically generated images, various analysis methods are compared and conclusions for their use are drawn. Results of the comparison show that the selection of a method …

Theory Of A Synchronously Pumped Mode-Locked Dye Laser In The Short Pump Pulse Limit, Duncan Leo Macfarlane, Lee W. Casperson

Electrical and Computer Engineering Faculty Publications and Presentations

We study the operation of a synchronously pumped mode-locked dye laser when the pump pulse is taken as a Dirac delta function, a limit that is sometimes experimentally reasonable. We find that in this limit the model simplifies considerably and that with further assumptions the physical interpretation of synchronously pumped mode-locked operation becomes apparent. Specifically, our nonlinear dynamical model reduces to the same set of equations that govern a prepumped Q-switched laser, and from this simple picture we are able to derive approximate analytic formulas for the synchronously pumped mode-locked laser pulse width and peak intensity. Additionally, we present a …

The Application Of The Ordered List Method And The Dynamic Programming To The Unit Commitment, Hoang Uong

Dissertations and Theses

The thesis presents a method of committing generating units in a hydro-thermal power system within practical computer resources such as computer time and data storage.

Direct Current-Excited Cw Co² Metal Waveguide Laser, Fahad S. Al-Mashaabi, Lee W. Casperson

Electrical and Computer Engineering Faculty Publications and Presentations

A novel design for a dc-excited cw CO₂ metal waveguide laser has been developed in which a slotted hollow cathode also doubles as a metal waveguide for the cavity modes. This design has been implemented in a compact structure that produces over 1 W of cw 10.6-µm radiation. The discharge characteristics, laser gain, and laser output have been studied as functions of various discharge parameters. The advantages of the transverse discharge of the slotted hollow cathode geometry include low voltage, positive impedance, rugged structure, and high optical gain. Overall efficiency is comparable with that of conventional longitudinal CO² lasers. The …

Pump Pulse Effects In Synchronously Pumped Mode-Locked Dye Lasers, Duncan Leo Macfarlane, Lee W. Casperson

Electrical and Computer Engineering Faculty Publications and Presentations

We consider the role of the pump pulse in the output of a synchronously pumped mode-locked dye laser. Our theoretical formalism is a nonlinear dynamical model that includes semiclassical effects, dipole orientation, and intrband relaxation. In particular, we study the shortenting of the output pulse with decreasing pump pulse length and increasing pump level. Both of these predictions agree with experiments.

Spontaneous Coherent Pulsations In Standing-Wave Laser Oscillators: Frequency Characteristics, Lee W. Casperson

Electrical and Computer Engineering Faculty Publications and Presentations

The output signal from a spontaneously pulsing laser must, by definition, consist of more than one frequency component. The experimental and theoretical study of the frequency components'associated with such a laser can provide valuable insights into the pulsation processes. The results of an investigation into the frequency characteristics of a spontaneously pulsing standing-wave laser are reported.

Application Of Hough Transformation To Detect Ovulatory Patterns In Cervical Mucus Images, Shiliang Wang

Dissertations and Theses

A microcomputer system called ovulocomputer is proposed. The system is used to predict and detect ovulation of women. It will use image processing and analysis, pattern recognition theory, spectrophotometry, ionometry and conductometry to measure various physical and chemical properties of cervical mucus that are related to blood hormone levels.

The functions and characteristics of cervical mucus are introduced in this thesis. Among them, the identification of cervical mucus images, named the ferning test, and related features, are well described.

A new idea, called ferning test automation, which has been neither proposed nor developed before, is presented and explained in detail …

The Effects Of Bandwidth Limiting Tuning Elements On A Synchronously Pumped Mode-Locked Dye Laser, Bahram Zandi

Dissertations and Theses

In this study an improved description of the bandwidth limiting tuning filters has been introduced into a semiclassical model for a synchronously pumped mode-locked dye laser system. This model is an improvement over the traditional rate equation approach since it has detailed representations of the energy levels, rotational distribution, and coherence effects. The new set of equations has been solved numerically using the best available values for the various parameters, and autocorrelations have been computed for a range of different length detuning and bandwidth limiting elements. In the experiments, an acousto-optically mode-locked argon ion laser is used to synchronously pump …

Ultrashort Pulse Production In Synchronously Pumped Mode-Locked Dye Laser Systems, Duncan Leo Macfarlane

Dissertations and Theses

The concern of this dissertation is the understanding and improvement of a class of lasers that is responsible for some of the shortest optical pulses available today. In particular, we seek ways to produce from synchronously pumped mode-locked dye laser systems, shorter pulses of higher intensity with improved pulse-to-pulse consistency. Specific topics.that are discussed herein include the study of the role of the pump pulse in synchronously pumped mode-locked lasers, the study of the pulse shaping and shortening due to an intracavity saturable absorber, and the study of a fundamental pulse train instability associated with these lasers.

A Finite State Machine Synthesizer, Jiuling Liu

Dissertations and Theses

This thesis presents a Finite State Machine (FSM) Synthesizer developed at Portland State University. The synthesizer starts from a high level behavioral description, in which no states are specified, and generates the lower level FSM descriptions for simulation and physical layout generation.

A New Approach To State Minimization Of Finite State Machines, William Yue Zhao

Dissertations and Theses

A complete program to ease the task of large scale Finite State Machine (FSM) minimization presented in this thesis: TDFM (Two Dimensional FSM Minimizer), is a part of the DIADES system. DIADES is an Automatic Design Synthesis System whose development in the Department of Electrical Engineering at Portland State University is supported in part by a research grant from SHARP Microelectronics Technology.

Parallel Architectures For Solving Combinatorial Problems Of Logic Design, Phuong Minh Ho

Dissertations and Theses

This thesis presents a new, practical approach to solve various NP-hard combinatorial problems of logic synthesis, logic programming, graph theory and related areas. A problem to be solved is polynomially time reduced to one of several generic combinatorial problems which can be expressed in the form of the Generalized Propositional Formula (GPF) : a Boolean product of clauses, where each clause is a sum of products of negated or non-negated literals.

Invariant Pattern Recognition Algorithm Using The Hough Transform, Duwang Li

Dissertations and Theses

A new algorithm is proposed which uses the Hough Transform to recognize two dimensional objects independent of their orientations, sizes and locations. The binary image of an object is represented by a set of straight lines. Features of the straight lines, namely the lengths and the angles of their normals, their lengths and the end point positions are extracted using the Hough Transform. A data structure for the extracted lines is constructed so that it is efficient to match the features of the lines of one object to those of another object, and determine if one object is a rotated …