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Articles 691 - 720 of 724
Full-Text Articles in Electrical and Computer Engineering
Thermal Hysteresis In Acoustic Resonators, Lee W. Casperson, Lloyd M. Davis, John D. Harvey
Thermal Hysteresis In Acoustic Resonators, Lee W. Casperson, Lloyd M. Davis, John D. Harvey
Electrical and Computer Engineering Faculty Publications and Presentations
In some applications of piezoelectrically driven acoustic resonators, the power dissipated in the resonating material may be sufficient to significantly change the temperature and hence the resonance frequency. A straightforward analysis shows that this effect can lead to severe hysteresis and thermal bistability. This model is in agreement with experiments that have been performed using a fused silica acousto‐optic modulator.
Modes Of A Laser Resonator With A Retroreflecting Corner Cube Mirror, Guosheng Zhou, Anthony J. Alfrey, Lee W. Casperson
Modes Of A Laser Resonator With A Retroreflecting Corner Cube Mirror, Guosheng Zhou, Anthony J. Alfrey, Lee W. Casperson
Electrical and Computer Engineering Faculty Publications and Presentations
The self-consistent integral equation for the field distribution of the resonant modes in a resonator with a tilted retroreflecting corner cube mirror is solved. The corner cube acts like a convex lens with radius of curvature -L cot²Ө in the rotation direction (L is the cavity length and Ө the rotation angle) and like a flat plane in the direction of the rotation axis. The field distribution can be described in terms of Hermite-Gaussian functions, and these results have been confirmed experimentally using an Ar-ion laser. The equivalent beam matrix for a reflecting corner cube is also found.
Modes Of A Laser Resonator With A Retroreflecting Roof Mirror, Guosheng Zhou, Lee W. Casperson
Modes Of A Laser Resonator With A Retroreflecting Roof Mirror, Guosheng Zhou, Lee W. Casperson
Electrical and Computer Engineering Faculty Publications and Presentations
The self-consistent integral equation for the field distribution of the resonant modes in a resonator with a tilted retroreflecting roof mirror is solved. The field distribution in the direction of the roof can be described in terms of Hermite-Gaussian functions. The beam matrix for a retroreflecting roof is found, and a new type of resonator which does not need precise alignment is proposed.
Electromagnetic Modes Of An Inhomogeneous Sphere, Lee W. Casperson
Electromagnetic Modes Of An Inhomogeneous Sphere, Lee W. Casperson
Electrical and Computer Engineering Faculty Publications and Presentations
In many cases the electromagnetic modes of a sphere can be obtained exactly. Special simplifications occur when the conductivity, complex permittivity, and complex permeability vary only in the radial direction, and static and time dependent examples are discussed. With quadratic or Coulomblike permittivity variations, the wave functions resemble the quantum mechanical harmonic oscillator or hydrogen atom wave functions, and similar angular momentum operators are obtained.
Synthesis Of Gaussian Beam Optical Systems, Lee W. Casperson
Synthesis Of Gaussian Beam Optical Systems, Lee W. Casperson
Electrical and Computer Engineering Faculty Publications and Presentations
Systematic procedures are presented for determining the the optical components needed to obtain an arbitrary transformation of a propagating light ray or Gaussian beam.
Modes Of A Laser Resonator With A Retroreflective Mirror, Guosheng Zhou, Lee W. Casperson
Modes Of A Laser Resonator With A Retroreflective Mirror, Guosheng Zhou, Lee W. Casperson
Electrical and Computer Engineering Faculty Publications and Presentations
The self-consistent integral equation for the field distribution of the resonant modes in an inclined retroreflective grating resonator is solved in the limit of large Fresnel numbers. The transverse field distribution in the direction perpendicular to the grating grooves can be described in terms of Hermite-Gaussian functions provided that λ « d « w, where λ is the wavelength, d is the grating spacing, and w is the beam spot size.
Laser Broadening Ratio From The Multimode Oscillation Threshold, Lee W. Casperson
Laser Broadening Ratio From The Multimode Oscillation Threshold, Lee W. Casperson
Electrical and Computer Engineering Faculty Publications and Presentations
Lasers with mixed line broadening typically oscillate in a single longitudinal mode for excitation levels only slightly above threshold. At high pump levels, less desirable multimode oscillation may sometimes occur. A procedure is described for using the multimode threshold as a sensitive measure of the broadening ratio, and GaAs is mentioned as an example.
Polarization Characteristics Of Dye‐Laser Amplifiers Ii. Isotropic Molecular Distributions, Lee W. Casperson, Kendall C. Reyzer
Polarization Characteristics Of Dye‐Laser Amplifiers Ii. Isotropic Molecular Distributions, Lee W. Casperson, Kendall C. Reyzer
Electrical and Computer Engineering Faculty Publications and Presentations
In a previous study a general semiclassical formalism has been developed for lasers with arbitrary orientational distributions of the active molecules. Here that formalism is applied to the important case of an isotropic distribution of molecules, and this limit is especially relevant to liquid dye lasers. Extensive analytical and numerical results are presented for the polarization properties of such dye lasers. It is found that in general the polarization states of the pump and signal fields are coupled together and both change with distance in a laser amplifier.
Polarization Characteristics Of Dye‐Laser Amplifiers I. Unidirectional Molecular Distributions, Lee W. Casperson, Kendall C. Reyzer
Polarization Characteristics Of Dye‐Laser Amplifiers I. Unidirectional Molecular Distributions, Lee W. Casperson, Kendall C. Reyzer
Electrical and Computer Engineering Faculty Publications and Presentations
Many practical laser amplifiers exhibit anisotropic gain due to polarization of the pumping fields or to a fixed preferential alignment of the active dipoles. Several specific causes and consequences of gain anisotropy are discussed in detail. In the analysis, the emphasis is placed on dye‐laser systems including arbitrary amplitudes, phases, and polarizations of the pump and signal fields. Analytical results are presented for a unidrectional molecular distribution, and it is found that the polarization states of the pump and signal fields change with distance in the amplifier.
Laser Power Calculations: Sources Of Error, Lee W. Casperson
Laser Power Calculations: Sources Of Error, Lee W. Casperson
Electrical and Computer Engineering Faculty Publications and Presentations
The physical phenomena that dominate the power characteristics of a laser depend on the detailed nature of the amplifying medium and the resonator structure. In predicting the power characteristics, numerous approximations are always required. The most important approximations are considered here in detail, and error estimates are presented so that a designer can select the appropriate model for a particular application. Emphasis is placed on analytic solutions and specific phenomena considered include longitudinal and transverse spatial hole burning, large single-pass gain, and mixed line broadening.
Properties Of A Coaxial Cw Co₂ Laser, T.-K. Cheng Ken, Lee W. Casperson
Properties Of A Coaxial Cw Co₂ Laser, T.-K. Cheng Ken, Lee W. Casperson
Electrical and Computer Engineering Faculty Publications and Presentations
A cw CO₂ laser has been developed in which the active medium is formed by a discharge between coaxial electrodes. The laser gain and saturation properties have been studied as functions of the various device parameters. Over-all efficiency is about the same as for a conventional longitudinal discharge laser, and advantages of the coaxial geometry include low voltage operation, rapid cooling, and rugged construction.
Scalar‐Wave Approach For Single‐Mode Inhomogeneous Fiber Problems, Lee W. Casperson, Cavour W. Yeh, W. P. Brown
Scalar‐Wave Approach For Single‐Mode Inhomogeneous Fiber Problems, Lee W. Casperson, Cavour W. Yeh, W. P. Brown
Electrical and Computer Engineering Faculty Publications and Presentations
It has generally been accepted that accurate results may be obtained using the scalar‐wave approach to solve problems dealing with inhomogeneous multimode guided‐wave structures. The problem of the applicability of the scalar‐wave approach to obtain wave propagation characteristics in single‐mode fiber or integrated optical circuit guides with inhomogeneous index profiles is examined in this paper. It is shown that if certain limiting conditions are satisfied, the scalar‐wave approach will yield valid results for single‐mode structures. These limiting conditions are usually satisfied by many practical single‐mode inhomogeneous fibers or IOC structures.
Beam Deflection In A Pulsed Chemical Laser Amplifier, J. Munch, Lee W. Casperson, E. C. Rea
Beam Deflection In A Pulsed Chemical Laser Amplifier, J. Munch, Lee W. Casperson, E. C. Rea
Electrical and Computer Engineering Faculty Publications and Presentations
Analyses and experiments have been performed to investigate deflection of a Gaussian beam propagating through an amplifying medium possessing a strong transverse gain gradient. The analysis includes effects due to dispersion and gain steering. The experiments were performed in a high power pulsed chemical laser amplifier using a cw frequency stabilized laser as a source. Time dependent beam deflection due to the interaction of the gain gradient with the finite radius of curvature of the propagating beam was observed.
Scattering Of Focused Beams By Tenuous Particles, S. Colak, Cavour W. Yeh, Lee W. Casperson
Scattering Of Focused Beams By Tenuous Particles, S. Colak, Cavour W. Yeh, Lee W. Casperson
Electrical and Computer Engineering Faculty Publications and Presentations
This paper deals with the problem of the scattering of focused laser beams by tenuous particles using an iterative technique. The results are shown to be accurate provided that (a) the polarizability of the particle medium is small and (b) the phase shift of the central ray is less than 2. It was found that when the size of the incident beam waist is close to that of the scatterer, the scattered field deviates significantly from that for the incident plane wave case. Specific examples are given.
Rayleigh-Debye Scattering With Focused Laser Beams, Lee W. Casperson, Cavour W. Yeh
Rayleigh-Debye Scattering With Focused Laser Beams, Lee W. Casperson, Cavour W. Yeh
Electrical and Computer Engineering Faculty Publications and Presentations
A focused beam technique has been developed for diagnosing the characteristics of individual particles within a polydisperse ensemble. In the Rayleigh-Debye approximation the scattered fields are related to the orientation and properties of a scatterer by means of explicit analytic formulas. The results simplify when the particle size is small compared to the minimum beam diameter.
Light Extinction In Polydisperse Particulate Systems, Lee W. Casperson
Light Extinction In Polydisperse Particulate Systems, Lee W. Casperson
Electrical and Computer Engineering Faculty Publications and Presentations
Analytic methods are developed for determining the attenuation characteristics of light beams propagating through ensembles of scattering particles including those with complex index of refraction. The methods are applicable to a wide range of practical particulate systems, and the results are expressed explicitly in terms of elementary functions. Propagation through fog and clouds is considered as an example, and it is found that absorption by the liquid lengths. water in such ensembles affects strongly the extinction for ir wave-lengths
Single Particle Scattering With Focused Laser Beams, Lee W. Casperson, Cavour W. Yeh
Single Particle Scattering With Focused Laser Beams, Lee W. Casperson, Cavour W. Yeh
Electrical and Computer Engineering Faculty Publications and Presentations
A scattering technique is described in which the incident laser beam is tightly focused to isolate the effects of a single particle. In this way the individual particles may be studied in their natural environment, and experiments with latex spheres are in agreement with the theory.
Threshold Characteristics Of Mirrorless Lasers, Lee W. Casperson
Threshold Characteristics Of Mirrorless Lasers, Lee W. Casperson
Electrical and Computer Engineering Faculty Publications and Presentations
Detailed analytical expressions are developed for the output power and spectral characteristics of high‐gain mirrorless laser amplifiers. With regard to intensity variations and spectral narrowing, such lasers are similar in behavior to conventional laser oscillators. A threshold transition region is apparent as saturation sets in, and spectral rebroadening occurs in inhomogeneously broadened laser systems. These solutions take full account of saturation by both the right and left propagating radiation, and the results agree with experiments that have been reported.
Beam Modes In Complex Lenslike Media And Resonators, Lee W. Casperson
Beam Modes In Complex Lenslike Media And Resonators, Lee W. Casperson
Electrical and Computer Engineering Faculty Publications and Presentations
General sets of higher-order beam modes are derived for light propagation in media having spatial variations of the gain or loss. The resulting expressions are also valid for propagation through conventional optical elements and graded transmission filters. The four basic mode sets obtained include off-axis Hermite-Gaussian and Laguerre-Gaussian modes of both real and complex argument. A procedure is developed for finding the resonant modes of laser oscillators containing arbitrary complex lens elements, and the mode stability properties of lasers can be interpreted physically by means of these formulas.
Pulse Evolution In Co₂ Lasers, Lee W. Casperson, M. J. Herbst, John J. Turechek
Pulse Evolution In Co₂ Lasers, Lee W. Casperson, M. J. Herbst, John J. Turechek
Electrical and Computer Engineering Faculty Publications and Presentations
Explicit formulas are examined for the development of optical pulses in gain‐switched or Q‐switched laser oscillators and for the distortion of such pulses in succeeding stages of laser amplification. The results are compared to data obtained with a TEA CO₂ oscillator‐amplifier system.
Analytic Modeling Of Gain‐Switched Lasers. Ii. Laser Amplifiers, Lee W. Casperson
Analytic Modeling Of Gain‐Switched Lasers. Ii. Laser Amplifiers, Lee W. Casperson
Electrical and Computer Engineering Faculty Publications and Presentations
The pulse transfer characteristics of gain‐switched laser amplifiers are investigated analytically. New closed‐form solutions have been obtained including arbitrary space‐ and time‐dependent pump distributions. The general results are specialzied to the important cases of uniform and traveling‐wave excitation. Input‐pulse shapes considered include step functions, practial oscillator output pulses, and also the inherent spontaneous‐emission noise. The results lead to improved models for pulse amplifiers and mirrorless traveling‐wave lasers. By proper choice of pump characteristics arbitrary output‐pulse waveforms can be synthesized.
Analytic Modeling Of Gain‐Switched Lasers. I. Laser Oscillators, Lee W. Casperson
Analytic Modeling Of Gain‐Switched Lasers. I. Laser Oscillators, Lee W. Casperson
Electrical and Computer Engineering Faculty Publications and Presentations
Detailed mathematical models are derived for the evolution of light pulses in gain‐switched laser oscillators. Unlike previous instantaneous‐switching models, arbitrary pump and spontaneous relaxation rates are considered. Explicit expressions are obtained for the gain and pulse characteristics in several practical situations, and both homogeneous and inhomogeneous limits are considered. By proper adjustment of the laser pump any output‐pulse shape can be obtained. The results are especially relevant for recent short‐pulse ultraviolet lasers and also for more conventional devices such as TEA CO₂ lasers.
Threshold Characteristics Of Multimode Laser Oscillators, Lee W. Casperson
Threshold Characteristics Of Multimode Laser Oscillators, Lee W. Casperson
Electrical and Computer Engineering Faculty Publications and Presentations
The oscillation characteristics of a multimode laser are considered in detail, and for the first time saturation by all of the cavity modes is included. Analytical expressions are obtained for the mode amplitudes, linewidths, and over‐all spectral characteristics of lasers operating above and below threshold. It is found that with increasing excitation the spontaneous emission spectrum is gradually resolved into a set of narrow discrete modes. Slightly above threshold the number of modes reduces in a homogeneoulsy broadened laser until only a single mode is oscillating strongly. The theoretical results are in agreement with experimental data that have been reported …
Mode Properties Of Annular Gain Lasers, Lee W. Casperson, Mohammad Shabbir Shekhani
Mode Properties Of Annular Gain Lasers, Lee W. Casperson, Mohammad Shabbir Shekhani
Electrical and Computer Engineering Faculty Publications and Presentations
The properties of a new class of laser resonators are investigated theoretically and experimentally. In these lasers the radiation propagates longitudinally in an annular amplifying medium, and useful low loss modes can be obtained even when the axial region is obscured. Alignment characteristics and far field patterns are discussed, and experiments have been conducted using coaxial double-discharge CO₂ devices.
Plasma Diagnosis By Laser Beam Scanning, Lee W. Casperson, T. K. Cheng
Plasma Diagnosis By Laser Beam Scanning, Lee W. Casperson, T. K. Cheng
Electrical and Computer Engineering Faculty Publications and Presentations
A procedure is developed for determining the radial electron density and temperature profiles of a rotationally symmetric plasma. This high‐resolution technique involves measuring the deflection of laser beams incident transverse to the plasma. Diagnosis of a stable atmospheric pressure argon arc with CO₂ and He‐Ne laser beams yields results in good agreement with spectroscopic methods.
Gaussian Modes In High Loss Laser Resonators, Lee W. Casperson, Susan D. Lunnam
Gaussian Modes In High Loss Laser Resonators, Lee W. Casperson, Susan D. Lunnam
Electrical and Computer Engineering Faculty Publications and Presentations
Matrix techniques are applied to the mode analysis of laser resonators having spherical mirrors and Gaussian profiles of the mirror reflectivity. These same analytical methods provide a useful approximation to the mode and loss characteristics of conventional resonators having an abrupt discontinuity of the reflectivity. Mode selection in apertured waveguides and resonators is also discussed.
Electromagnetic Modes Of An Inhomogeneous Sphere, Lee W. Casperson
Electromagnetic Modes Of An Inhomogeneous Sphere, Lee W. Casperson
Electrical and Computer Engineering Faculty Publications and Presentations
Vector wave solutions are derived for the electromagnetic modes of a sphere having radial variations of the refractive index and gain. For some inhomogeneity models, confined-mode solutions exist. The results are applicable to the refracting atmospheres of stars and planets.
Output Properties Of Short-Pulse Gain-Switched Lasers, Lee W. Casperson
Output Properties Of Short-Pulse Gain-Switched Lasers, Lee W. Casperson
Electrical and Computer Engineering Faculty Publications and Presentations
A formalism is derived for analyzing the spectral and temporal properties of gain-switched lasers. The development of the longitudinal mode structure from spontaneous emission, limiting linewidths, and over-all spectral characteristics are considered in detail; and applications are discussed.
Air Breakdown In A Radial-Mode Focusing Element, Lee W. Casperson, Mohammad Shabbir Shekhani
Air Breakdown In A Radial-Mode Focusing Element, Lee W. Casperson, Mohammad Shabbir Shekhani
Electrical and Computer Engineering Faculty Publications and Presentations
A new radial focusing device is described that condenses an incident laser beam to an extremely intense and uniformly illuminated focal spot. The focal region is useful for many applications. When used with a 10.6-µm CO₂ TEA laser source, a disk-shaped air-breakdown spark results, and the properties of this spark have been investigated.
Gaussian Light Beams In Inhomogeneous Media, Lee W. Casperson
Gaussian Light Beams In Inhomogeneous Media, Lee W. Casperson
Electrical and Computer Engineering Faculty Publications and Presentations
Vector wave solutions are obtained for the propagation of beams of light in media having slow spatial variations of the gain, loss, or index of refraction. The formalism developed here is applicable to a wide range of problems, and an exa mple considered in detail is the propagation of off-axis beams in lenslike laser materials and optical waveguides. A procedure is also described for the diagnosis of localized dielectric inhomogeneities such as plasmas by means of Gaussian laser beams.