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Electrical and Computer Engineering Faculty Publications and Presentations

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Articles 661 - 690 of 724

Full-Text Articles in Electrical and Computer Engineering

Ultrashort‐Pulse Propagation In Dye Laser Amplifiers, Shuanghua Jiang, Lee W. Casperson Jan 1993

Ultrashort‐Pulse Propagation In Dye Laser Amplifiers, Shuanghua Jiang, Lee W. Casperson

Electrical and Computer Engineering Faculty Publications and Presentations

A semiclassical model is presented for ultrashort‐pulse dye laser amplifiers. The model permits a discussion of important aspects of short‐pulse amplification such as pulse shape, pulse energy, and gain saturation. Coherence effects are found to be important in characterizing the evolution of amplified pulses in the subpicosecond and femtosecond regimes. The results are compared with those obtained using the corresponding rate equation model.

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New Speckle Technique For Noncontact Measurement Of Small Creep Rates, Donald D. Duncan, F. Fausten Mark, Lawrence W. Hunter Jul 1992

New Speckle Technique For Noncontact Measurement Of Small Creep Rates, Donald D. Duncan, F. Fausten Mark, Lawrence W. Hunter

Electrical and Computer Engineering Faculty Publications and Presentations

A highly sensitive method for measuring thermal expansion, mechanical strain, and creep rates has been developed. This technique is based on Yamaguchi's speckle strain gauge concept, but uses a novel data-processing approach that provides estimates of the time rate of inplane strain. The approach is appropriate for assessing very small strain rates in hostile environments. It provides simultaneous global estimates of the strain at both small and large gauge sizes. This may be of importance in studying materials with different short- and long-range orders. General advantages of the technique are compact design, modest resolution requirements, insensitivity to surface microstructure changes …

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Rotating-Wave Approximation In High-Gain Lasers, Lee W. Casperson Jul 1992

Rotating-Wave Approximation In High-Gain Lasers, Lee W. Casperson

Electrical and Computer Engineering Faculty Publications and Presentations

Semiclassical models for lasers typically incorporate a fundamental simplification called the rotating-wave approximation. In this study the rotating-wave approximation is reexamined, and its implications for the simplest problem of a steady-state laser oscillator are considered in detail. It is found that for practical laser operating conditions the errors resulting from this approximation may not always be negligible.

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Field-Equation Approximations And Amplification In High-Gain Lasers: Numerical Results, Lee W. Casperson Sep 1991

Field-Equation Approximations And Amplification In High-Gain Lasers: Numerical Results, Lee W. Casperson

Electrical and Computer Engineering Faculty Publications and Presentations

It has recently been shown that a field-equation time-derivative approximation that is commonly used in studies of laser-oscillator dynamics is not necessary and can lead to significant errors for some lasers. A related space-derivative approximation is widely used in studies of steady-state laser amplifiers. A more rigorous amplifier formalism is developed here, and the results are exact solutions of Maxwell’s equations. The improved model predicts a spatial instability, single mirror oscillation, and other interesting field behavior.

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Field-Equation Approximations And Amplification In High-Gain Lasers: Analytical Results, Lee W. Casperson Sep 1991

Field-Equation Approximations And Amplification In High-Gain Lasers: Analytical Results, Lee W. Casperson

Electrical and Computer Engineering Faculty Publications and Presentations

In a related study the equations governing a high-gain laser amplifier have been solved numerically without making the usual slowly-varying-amplitude derivative approximation in Maxwell’s equations, and thus the field amplitudes are not restricted to vary negligibly in a distance of one wavelength. The results reveal an instability that involves reflections and oscillatory growth of perturbations away from steady state. In the present study steady-state solutions of the field equations are obtained analytically, and transformations are described for converting the equations to alternative intensity-equation sets. These intensity equations are linearized and solved for the growth rate and oscillation period of the …

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Pump Polarization Effects In Cw Dye Lasers, Lee W. Casperson, W. J. Sandle, A. C. Wilson, D. M. Warrington, R. J. Ballagh Jun 1991

Pump Polarization Effects In Cw Dye Lasers, Lee W. Casperson, W. J. Sandle, A. C. Wilson, D. M. Warrington, R. J. Ballagh

Electrical and Computer Engineering Faculty Publications and Presentations

The effects of pump polarization on the performance of cw dye lasers have been investigated. A recently developed semiclassical model for synchronously pumped mode‐locked dye lasers is adapted to the problem of cw dye‐laser oscillation, and analytic expressions are obtained for the relationship between the pump power, pump polarization, and dye‐laser output power. The theoretical results are compared with experimental data obtained using an argon‐laser‐pumped rhodamine 6G dye laser.

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Field-Equation Approximations And The Dynamics Of High-Gain Lasers, Lee W. Casperson May 1991

Field-Equation Approximations And The Dynamics Of High-Gain Lasers, Lee W. Casperson

Electrical and Computer Engineering Faculty Publications and Presentations

Semiclassical models for laser-dynamics studies typically incorporate a derivative approximation that reduces the second-order wave equation for the electric field to a first-order equation. It is shown here that this approximation and further frequency approximations are not necessary and may lead to significant errors for some high-gain laser systems. A more exact analysis also reveals a partial decoupling of the electric and magnetic fields that occurs with fast transient phenomena. These ideas are illustrated in terms of well-known dynamical effects.

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Oscillation Frequency In High-Gain Lasers, Lee W. Casperson Dec 1990

Oscillation Frequency In High-Gain Lasers, Lee W. Casperson

Electrical and Computer Engineering Faculty Publications and Presentations

The calculation of the oscillation frequency of a single-mode laser oscillator is examined systematically. Mode-pulling formulas are developed for a variety of laser systems, and the limitations of a standard approximation are explored.

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Spontaneous Coherent Pulsations In Standing-Wave Laser Oscillators: Simplified Models, Lee W. Casperson, Manuela Fe Tarroja Apr 1990

Spontaneous Coherent Pulsations In Standing-Wave Laser Oscillators: Simplified Models, Lee W. Casperson, Manuela Fe Tarroja

Electrical and Computer Engineering Faculty Publications and Presentations

A series of simplifications and approximations is introduced into a recently described model for spontaneous pulsations in standing-wave laser oscillators. To the extent that these simplifications are valid they can lead to significant reductions in computation time and sometimes also to a better understanding of the relative importance of various physical effects. Of special interest is the number of spatial harmonics required to represent adequately the effects of longitudinal spatial hole burning. Other approximations investigated include neglect of spectral cross relaxation, neglect of multiple-energy-level equations, neglect of electric-field derivatives, and neglect of polarization derivatives. In addition, a detailed discussion is …

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Pulse-Train Instabilities Of A Synchronously Pumped Mode-Locked Dye Laser: Experimental Phase Plots, Duncan Leo Macfarlane, Lee W. Casperson Mar 1990

Pulse-Train Instabilities Of A Synchronously Pumped Mode-Locked Dye Laser: Experimental Phase Plots, Duncan Leo Macfarlane, Lee W. Casperson

Electrical and Computer Engineering Faculty Publications and Presentations

We present experimental phase plots of the pulse-train instability that occurs in synchronously pumped mode-locked dye lasers. From these plots we infer that the instability is of a quasi-periodic, nonlinear dynamical nature. Further, we note that the information lost in this two-dimensional representation is precisely the periodic-versus-erratic character and therefore is of considerable importance.

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Effects Of Bandwidth‐Limiting Tuning Elements In Synchronously Pumped Mode‐Locked Lasers, Bahram Zandi, Lee W. Casperson, Duncan Leo Macfarlane Mar 1990

Effects Of Bandwidth‐Limiting Tuning Elements In Synchronously Pumped Mode‐Locked Lasers, Bahram Zandi, Lee W. Casperson, Duncan Leo Macfarlane

Electrical and Computer Engineering Faculty Publications and Presentations

A description of bandwidth‐limiting tuning filters is introduced into a semiclassical model for synchronously pumped mode‐locked dye lasers. The finite phase memory of the molecular wave functions is included as are the isotropic molecular distribution and the finite vibrational relaxation times. The new set of equations has been solved numerically using the best available values for the various parameters. The results have been compared with experimental data obtained using a rhodamine 6G dye laser, which is synchronously pumped using an acousto‐optically mode‐locked argon laser. Tuning element effects have been studied using two‐ and three‐plate birefringent filters and a tuning wedge, …

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Spontaneous Mode Locking In Long-Cavity Xenon Lasers, Manuela Fe Tarroja, Mohammad Sharafi, Lee W. Casperson Aug 1989

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.

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Theory Of A Synchronously Pumped Mode-Locked Dye Laser In The Short Pump Pulse Limit, Duncan Leo Macfarlane, Lee W. Casperson Jun 1989

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 …

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Direct Current-Excited Cw Co² Metal Waveguide Laser, Fahad S. Al-Mashaabi, Lee W. Casperson May 1989

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 …

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Pump Pulse Effects In Synchronously Pumped Mode-Locked Dye Lasers, Duncan Leo Macfarlane, Lee W. Casperson Mar 1989

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.

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Spontaneous Coherent Pulsations In Standing-Wave Laser Oscillators: Frequency Characteristics, Lee W. Casperson Mar 1989

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.

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The Lunar Date Of Ramesses Ii, Lee W. Casperson Jul 1988

The Lunar Date Of Ramesses Ii, Lee W. Casperson

Electrical and Computer Engineering Faculty Publications and Presentations

Due largely to the efforts of R. A. Parker, the various calendars used in Egypt are now fairly well understood. Dates which the Egyptians expressed in both their civil and lunar calendars can sometimes be determined exactly, and the study of such dates has been extremely important in efforts to establish an accurate Egyptian chronology. However, the successful use of this method obviously depends on one's ability to reconstruct accurately the astronomical and observational conditions on which the lunar calendar was based. The author re-examined the methods used to calculate lunar dates and have suggested some ways in which those …

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Spectral Behavior And Pulse Train Instabilities Of A Synchronously Pumped Mode-Locked Dye Laser, Duncan Leo Macfarlane, Lee W. Casperson, Anthony A. Tovar May 1988

Spectral Behavior And Pulse Train Instabilities Of A Synchronously Pumped Mode-Locked Dye Laser, Duncan Leo Macfarlane, Lee W. Casperson, Anthony A. Tovar

Electrical and Computer Engineering Faculty Publications and Presentations

The pulse-train envelope of a synchronously pumped mode-locked dye laser has been experimentally studied as a function of cavity length detuning. When a bandwidth-limiting birefringent tuning filter is included and the cavity is adjusted to the length that yields optimally short (˜2-psec) pulse, there is a slow (≤800 kHz), erratic amplitude modulation that provides a 20% variation in pulse energies. As the cavity length is detuned on the order of one part in 10⁴, the modulation vanishes, but the individual pulse lengths increade dramtically. Further detuning results in a clean periodic envelope with a 20% modulation depth and a˜5-μsec period. …

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Spontaneous Coherent Pulsations In Standing-Wave Laser Oscillators, Lee W. Casperson May 1988

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

Electrical and Computer Engineering Faculty Publications and Presentations

Spontaneous pulsation phenomena in xenon lasers are now well known, and related effects have been observed with other laser types. Most theoretical analyses of such pulsations are formulated for unidirectional ring lasers, whereas most experiments involve standing-wave resonator geometries. Described here are rigorous semiclassical models governing the spontaneous pulsation instability in standing-wave laser oscillators. The standing-wave results are more complex and closer to experimental observations than the ring results for operation in the Lambdip region near line center.

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Pulse-Train Instabilities In A Mode-Locked Argon Laser: Experimental Studies, Duncan Leo Macfarlane, Lee W. Casperson Nov 1987

Pulse-Train Instabilities In A Mode-Locked Argon Laser: Experimental Studies, Duncan Leo Macfarlane, Lee W. Casperson

Electrical and Computer Engineering Faculty Publications and Presentations

The output train of pulses from an acousto-optically mode-locked argon-ion laser was studied as a function of the loss modulation frequency for small detunings from the optimum c/2L modulation. A shift away from the optimum frequency by as little as 1 part in 10⁴ was found to produce several strong lower-frequency components that amplitude modulate the mode-locked pulse train. Notably, the strongest subharmonic is a frequency near ƒopt/4. Further detuning results in an irregular, slow (of the order of 10⁵ Hz) amplitude envelope on the pulse train. The homodyne spectrum of this phase of operation represents a progressive filling-in behavior …

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Metal Waveguide Modeling Of Tapered Quadratic Index Media, Lee W. Casperson, Bahram Zandi Dec 1986

Metal Waveguide Modeling Of Tapered Quadratic Index Media, Lee W. Casperson, Bahram Zandi

Electrical and Computer Engineering Faculty Publications and Presentations

The basic electromagnetic properties of tapered graded index fibers are equivalent to the properties of a class of concave metallic waveguides. Although useful in their own right, such metal waveguides also provide a straightforward and inexpensive means for studying the characteristics of more complicated tapered media.

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Beam Propagation In Periodic Quadratic-Index Waveguides, Lee W. Casperson Dec 1985

Beam Propagation In Periodic Quadratic-Index Waveguides, Lee W. Casperson

Electrical and Computer Engineering Faculty Publications and Presentations

Several techniques are described for studying the propagation of off-axis polynomial Gaussian beams in media having straight axes and periodic z variations of the quadratic refraction and loss coefficients. For some periodic variations, exact analytical solutions of the paraxial equations are possible, and for sufficiently slow variations, WKB solutions can always be obtained. All results are expressed in conventional beam matrix form.

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Spontaneous Coherent Pulsations In Ring-Laser Oscillators: Stability Criteria, Lee W. Casperson Jun 1985

Spontaneous Coherent Pulsations In Ring-Laser Oscillators: Stability Criteria, Lee W. Casperson

Electrical and Computer Engineering Faculty Publications and Presentations

The stability criteria implied by a simplified semiclassical laser model are considered in detail. It is found that two types of criteria must be distinguished. The first concerns the smallest pump rate for which infinitesimal perturbations of the steady-state solution will increase with time, and the second concerns the smallest pump rate for which large amplitude modulations will not damp away.

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Spontaneous Coherent Pulsations In Ring-Laser Oscillators, Lee W. Casperson Jan 1985

Spontaneous Coherent Pulsations In Ring-Laser Oscillators, Lee W. Casperson

Electrical and Computer Engineering Faculty Publications and Presentations

Complex spontaneous-pulsation phenomena have been reported in xenon lasers operating at 3.51-μm wavelength, and a theoretical explanation for these effects has been given. However, the published models contain various simplifications and have so far yielded only qualitative agreement with xenon-laser experiments. Reported here is a more rigorous analytical model, which for the first time provides quantitative agreement with experimental observations. This model should also find direct application in interpreting or predicting the behavior of other spontaneously pulsing laser systems.

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Solvable Hill Equation, Lee W. Casperson Nov 1984

Solvable Hill Equation, Lee W. Casperson

Electrical and Computer Engineering Faculty Publications and Presentations

A second-order linear differential equation with continuous periodic coefficients is solved exactly in terms of elementary functions. Equations of this type arise commonly in several areas of physics, and the solutions may find practical applications. As an illustration, the results are applied to the problem of an electron in a one-dimensional periodic potential.

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Power Characteristics Of Single‐Mode Semiconductor Lasers, Jaroslava Z. Wilcox, Lee W. Casperson Jul 1984

Power Characteristics Of Single‐Mode Semiconductor Lasers, Jaroslava Z. Wilcox, Lee W. Casperson

Electrical and Computer Engineering Faculty Publications and Presentations

The basic aspects of power calculations for high‐gain semiconductor lasers are briefly reviewed, and a straightforward one‐dimensional model is described. The relative importance of spontaneous emission, distributed losses, band‐to‐band absorption, and high single‐pass gain are investigated in detail.

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Propagation Of Airy-Hermite-Gaussian Waveguide Modes In Free Space, Lee W. Casperson, O. M. Stafsudd, Leroy V. Sutter, Jonathan Gary Grossman Jan 1984

Propagation Of Airy-Hermite-Gaussian Waveguide Modes In Free Space, Lee W. Casperson, O. M. Stafsudd, Leroy V. Sutter, Jonathan Gary Grossman

Electrical and Computer Engineering Faculty Publications and Presentations

The cavity modes of metal strip waveguide lasers are most simply expressed in terms of Airy-Hermite-Gaussian functions. The free space propagation of the resulting beam modes has been examined, and both near- and far-field patterns have been calculated and measured. Phase plates may be useful for enhancing the far-field intensity.

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Lateral Coherence Of Aerosol-Scattered Laser Radiation, Donald D. Duncan, D. E. Larch Dec 1983

Lateral Coherence Of Aerosol-Scattered Laser Radiation, Donald D. Duncan, D. E. Larch

Electrical and Computer Engineering Faculty Publications and Presentations

To assess the probability of detection (by interferometric techniques) of illumination by a coherent source, we characterize the lateral coherence of the off-axis aerosol scattered radiation by applying the van Cittert-Zernike theorem. We find that, for 1.061-pm radiation at a target range of 1 km, the scattered radiation beyond 3.5 cm off axis does not display appreciable lateral coherence.

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Radio-Frequency-Excited Carbon Dioxide Metal Waveguide Laser, Jonathan Gary Grossman, Lee W. Casperson, O. M. Stafsudd May 1983

Radio-Frequency-Excited Carbon Dioxide Metal Waveguide Laser, Jonathan Gary Grossman, Lee W. Casperson, O. M. Stafsudd

Electrical and Computer Engineering Faculty Publications and Presentations

A new type of waveguide laser is described in which a single-surface concave metal waveguide also doubles as the grounded electrode in a radio-frequency-excited gaseous discharge. The laser’s output modes and spectrum have been studied theoretically and experimentally for cw CO₂ operation of the laser. Overall operating efficiency and mode stability are comparable with those of conventional dielectric waveguide CO₂ lasers, and advantages of the metal waveguide laser include convection cooling, intracavity mode control, and partial self-alignment.

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Coherence Effects In Synchronously Pumped Mode‐Locked Dye Lasers, Lee W. Casperson Oct 1982

Coherence Effects In Synchronously Pumped Mode‐Locked Dye Lasers, Lee W. Casperson

Electrical and Computer Engineering Faculty Publications and Presentations

A formalism is developed for describing the evolution of picosecond mode‐locked pulses in synchronously pumped dye lasers. The finite phase memory of the molecular wave functions is included, and it is found that the resultant coherence effects can be dominant for operation close to exact synchrony. Considerations of the isotropic molecular orientational distribution and the finite vibrational relaxation times are also essential in obtaining quantitative agreement with experimental results.

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