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Articles 181 - 210 of 283

Full-Text Articles in Physics

Comment On A Critique Of The Instantaneous Normal Mode (Inm) Approach To Diffusion, T. Keyes, Wu Xiong Li, Ulrich Zurcher Sep 1998

Comment On A Critique Of The Instantaneous Normal Mode (Inm) Approach To Diffusion, T. Keyes, Wu Xiong Li, Ulrich Zurcher

Physics Faculty Publications

A critique of the instantaneous normal mode (INM) theory of diffusion by Gezelter, Rabani, and Berne (GRB) [J. Chem. Phys. 107, 4618 (1997)] is analyzed. GRB assert that imaginary-frequency INM are corrupted with modes unrelated to barrier crossing, that proposals for removing such nondiffusive (ND) modes are inadequate, and thus that INM cannot be used to predict the self-diffusion constant, D. In rebuttal it is argued that Lennard-Jones, the system studied by GRB, is anamolously rich in ND modes. INM in molecular liquids are shown to behave as excellent indicators of barrier crossing. Even in LJ ND-INM, while plentiful, do …

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Spiral Morphology-Dependent Resonances In An Optical Fiber: Effects Of Fiber Tilt And Focused Gaussian Beam Illumination, Andrew W. Poon, Richard K. Chang, James A. Lock Jul 1998

Spiral Morphology-Dependent Resonances In An Optical Fiber: Effects Of Fiber Tilt And Focused Gaussian Beam Illumination, Andrew W. Poon, Richard K. Chang, James A. Lock

Physics Faculty Publications

Spiral morphology-dependent resonances have been observed in a tilted optical fiber. The polarization-preserving and the cross-polarized elastic-scattering spectra for plane-wave illumination show that the wavelengths of the resonances are blueshifted quadratically as the fiber tilt angle increases. When a focused Gaussian beam illuminates the fiber at its edge, the resonances are blueshifted and broadened as the detector is offset from the scattering plane with the maximum scattering intensity. The blueshift with focused beam illumination is also a consequence of the spiral resonances. (C) 1998 Optical Society of America.

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Translational Diffusion Of Small And Large Mesoscopic Probes In Hydroxypropylcellulose-Water In The Solutionlike Regime, Kiril A. Streletzky, George D.J. Phillies Jun 1998

Translational Diffusion Of Small And Large Mesoscopic Probes In Hydroxypropylcellulose-Water In The Solutionlike Regime, Kiril A. Streletzky, George D.J. Phillies

Physics Faculty Publications

Quasi-elastic light scattering spectroscopy was used to study the translational diffusion of monodisperse spheres in aqueous 1 MDa hydroxypropylcellulose (HPC) at 25 °C. Probe diameters d spanned 14–455 nm; HPC concentrations were 0⩽c⩽7g/L. Light scattering spectroscopy consistently found spectra having the form g(1)(t)=(1−Af)exp(−θtβ)+Af exp(−θftβf). Here θf and βf refer to the “fast” mode; θ and β describe the “slow” mode. We examine the dependence of θ, β, θf, βf, and Af on d, c, scattering vector q, and viscosity η. β=1 for large probes; elsewise, β and βf are ∈(0,1). The slow mode, with short-lived memory function, is diffusive; for …

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Amplification Of High-Order Rainbows Of A Cylinder With An Elliptical Cross Section, James A. Lock, Charles L. Adler, Bradley R. Stone, Patrick D. Zajak Mar 1998

Amplification Of High-Order Rainbows Of A Cylinder With An Elliptical Cross Section, James A. Lock, Charles L. Adler, Bradley R. Stone, Patrick D. Zajak

Physics Faculty Publications

The intensity of high-order rainbows for normally incident light and certain rotation angles of a cylinder with an elliptical cross section is greatly amplified with respect to the intensity for a circular cross-sectional cylinder. The amplification is due to a number of the internal reflections occurring past the critical angle for total internal reflection, and the effect is especially strong for odd-order rainbows, beginning with the third order. Experimentally, the fourth-and the fifth-order rainbows of a nearly elliptical cross-sectional glass rod were observed and analyzed. (C) 1998 Optical Society of America.

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Rainbow Scattering By A Cylinder With A Nearly Elliptical Cross Section, Charles L. Adler, James A. Lock, Bradley R. Stone Mar 1998

Rainbow Scattering By A Cylinder With A Nearly Elliptical Cross Section, Charles L. Adler, James A. Lock, Bradley R. Stone

Physics Faculty Publications

We both theoretically and experimentally examine the behavior of the first-and the second-order rainbows produced by a normally illuminated glass rod, which has a nearly elliptical cross section, as it is rotated about its major axis. We decompose the measured rainbow angle, taken as a function of the rod's rotation angle, into a Fourier series and find that the rod's refractive index, average ellipticity, and deviation from ellipticity are encoded primarily in the m = 0, 2, 3 Fourier coefficients, respectively. We determine these parameters for our glass rod and, where possible, compare them with independent measurements. We find that …

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Ray Theory Analysis Of The Shadow Blister Effect, James A. Lock Mar 1998

Ray Theory Analysis Of The Shadow Blister Effect, James A. Lock

Physics Faculty Publications

When an extended light source such as the Sun illuminates two objects so that their shadows lie close to each other, the shadow of one of the objects occasionally appears to bulge out toward the shadow of the other. This effect is caused by the overlap of the penumbras of the shadows and is analyzed here with ray theory. A laboratory demonstration of this phenomenon is performed and compared with theoretical predictions. (C) 1998 Optical Society of America.

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Three-Dimensional Camera Calibration Technique For Stereo Imaging Velocimetry Experiments, Mark D. Bethea, James A. Lock, Frank Merat, Paul Crouser Dec 1997

Three-Dimensional Camera Calibration Technique For Stereo Imaging Velocimetry Experiments, Mark D. Bethea, James A. Lock, Frank Merat, Paul Crouser

Physics Faculty Publications

A three-dimensional camera calibration technique is developed by combining two, 2-D camera calibrations for an orthogonal stereo viewing geometry. The left camera view (YZ view) and the right camera view (XZ view) are calibrated separately and then combined to produce an XYZ (3-D) calibration routine, Our technique employs three parallel calibration planes. One is placed along the main diagonal of the cubic experimental chamber, and the other two planes are placed known distances in front of it and behind it within the chamber. Both cameras view the calibration points on the planes simultaneously. Given the coordinates of a number of …

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Role Of Multiple Scattering In Cross-Correlated Light Scattering With A Single Laser Beam, James A. Lock Oct 1997

Role Of Multiple Scattering In Cross-Correlated Light Scattering With A Single Laser Beam, James A. Lock

Physics Faculty Publications

Previous systems for measuring cross-correlated light scattering by small particles suspended in a liquid with multiple-scattering suppression have illuminated the particles with two laser beams. It is shown that multiple-scattering suppression should also occur in cross correlation for a system that employs a single laser beam and two closely spaced detectors with wide fields of view. The single-scattering, double-scattering, and single-double-scattering cross-term contributions to the intensity cross-correlation function are calculated. It is found that the two cross terms, when added together, are unimportant for both autocorrelation and cross correlation. The amplitude of the double-scattering term can be greatly diminished by …

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Hybrid Reflection-Transmission Surface Light-Scattering Instrument With Reduced Sensitivity To Surface Sloshing, William V. Meyer, James A. Lock, H. Michael Cheung, Thomas W. Taylor, Padetha Tin, J. Adin Mann Oct 1997

Hybrid Reflection-Transmission Surface Light-Scattering Instrument With Reduced Sensitivity To Surface Sloshing, William V. Meyer, James A. Lock, H. Michael Cheung, Thomas W. Taylor, Padetha Tin, J. Adin Mann

Physics Faculty Publications

A hybrid reflection-transmission surface light-scattering instrumental design is presented, examined theoretically, and tested experimentally. The purpose of the design is to reduce the sensitivity of the instrument to vibration in general and surface sloshing in particular while sacrificing Little performance. Traditional optical arrangements and two new optical configurations with varying trade-offs between slosh resistance and instrumental simplicity and accuracy are examined by use of Fourier optics methods. The most promising design was constructed and tested with acetone, ethanol, and water as subject fluids. The test involved backcalculation of the wave number of the capillary wave examined with the known physical …

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Multiple-Scattering Suppression By Cross Correlation, William V. Meyer, David S. Cannell, Anthony E. Smart, Thomas W. Taylor, Padetha Tin Oct 1997

Multiple-Scattering Suppression By Cross Correlation, William V. Meyer, David S. Cannell, Anthony E. Smart, Thomas W. Taylor, Padetha Tin

Physics Faculty Publications

We describe a new method for characterizing particles in turbid media by cross correlating the scattered intensity fluctuations at two nearby points in the far field. The cross-correlation function selectively emphasizes single scattering over multiple scattering. The usual dynamic light-scattering capability of inferring particle size from decay rate is thus extended to samples that are so turbid as to be visually opaque. The method relies on single-scattering speckle being physically larger than multiple-scattering speckle. With a suitable optical geometry to select nearby points in the far field or equivalently slightly different scattering wave vectors (of the same magnitude), the multiple-scattering …

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Fiber-Optics Surface-Light-Scattering Spectrometer, Padetha Tin, J. Adin Mann, William V. Meyer, Thomas W. Taylor Oct 1997

Fiber-Optics Surface-Light-Scattering Spectrometer, Padetha Tin, J. Adin Mann, William V. Meyer, Thomas W. Taylor

Physics Faculty Publications

We have developed a fiber-optics surface-light-scattering spectrometer completely designed with optical fiber components. To the best of our knowledge, this is the first demonstration of a noninvasive measurement of the surface tension and the viscosity of simple liquid-vapor interfaces with a fiber-optics-based sensor system. With this approach we obtain a compact size, a significant increase in the signal-to-noise ratio, and the ability to select from a continuum of wave vectors. (C) 1997 Optical Society of America.

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Study Of The Effects Of Initial-Bred Nuclei On Zeolite Naa Crystallization By Quasi-Elastic Light Scattering Spectroscopy And Electron Microscopy, Leszek Gora, Kiril A. Streletzky, Robert W. Thompson, George D.J. Phillies Sep 1997

Study Of The Effects Of Initial-Bred Nuclei On Zeolite Naa Crystallization By Quasi-Elastic Light Scattering Spectroscopy And Electron Microscopy, Leszek Gora, Kiril A. Streletzky, Robert W. Thompson, George D.J. Phillies

Physics Faculty Publications

Synthesis studies have been conducted at 25, 60, and 80 °C with a clear solution batch composition that produces zeolite NaA. Aluminosilicate precursor material was added to promote the synthesis and to evaluate the effects of adding initial-bred nuclei that were created by a precursor “seed” reaction. It is shown that the initial-bred nuclei promoted the crystallization rate, that the crystalline mass produced was increased when using the initial-bred nuclei, and that the nucleation of a second population was not inhibited by the addition of initial-bred nuclei as seeds.

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Monte Carlo Study Of The Square-Lattice Annealed Ising Model On Percolating Clusters, P. D. Scholten, Miron Kaufman Jul 1997

Monte Carlo Study Of The Square-Lattice Annealed Ising Model On Percolating Clusters, P. D. Scholten, Miron Kaufman

Physics Faculty Publications

Simulations of an Ising q-state Pods model which is equivalent to the Ising model on annealed percolation clusters are used to determine the phase diagram of the model in two dimensions. Three topologically different phase diagrams are obtained: (i) for q=2, there are two critical Ising lines meeting at T=0 at the four-state Potts critical point; (ii) for 24, the Ising:critical line intersects a Line of first-order transitions at a critical end point.

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Anharmonic Potentials In Supercooled Liquids: The Soft-Potential Model, Ulrich Zürcher, T. Keyes Jun 1997

Anharmonic Potentials In Supercooled Liquids: The Soft-Potential Model, Ulrich Zürcher, T. Keyes

Physics Faculty Publications

Instantaneous normal modes (INM) are the harmonic approximation to liquid dynamics. This is an extension of the phonon description of lattice dynamics, in which case Bloch's theorem shows that all modes are extended. Long-range order is destroyed in liquids and glasses, and the INM spectrum has contributions from both extended and localized modes. We use the soft-potential mode to describe localized modes. This model is a high-temperature extension of the standard two-level-system model for glasses. The equilibrium position of any atom in the liquid has only temporary character, and relaxation processes in the liquid are associated with particles hopping over …

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High-Order Interior Caustics Produced In Scattering Of A Diagonally Incident Plane Wave By A Circular Cylinder, Charles L. Adler, James A. Lock, Bradley R. Stone, Claudio J. Garcia Jun 1997

High-Order Interior Caustics Produced In Scattering Of A Diagonally Incident Plane Wave By A Circular Cylinder, Charles L. Adler, James A. Lock, Bradley R. Stone, Claudio J. Garcia

Physics Faculty Publications

We examine scattering of a family of initially parallel diagonally incident rays by a dielectric circular cylinder and show that the interior and exterior caustics that occur are qualitatively identical to those produced at normal incidence. We find, however, that (1) varying the plane-wave tilt angle has the same effect on the caustics as varying the refractive index of the cylinder at normal incidence and (2) high-order interior caustics are visible because of larger internal-reflection Fresnel coefficients at diagonal incidence than at normal incidence. We also observe noncaustic ray trajectories produced by the sharp peaking of internal-reflection Fresnel coefficients at …

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Debye-Series Analysis Of The First-Order Rainbow Produced In Scattering Of A Diagonally Incident Plane Wave By A Circular Cylinder, James A. Lock, Charles L. Adler Jun 1997

Debye-Series Analysis Of The First-Order Rainbow Produced In Scattering Of A Diagonally Incident Plane Wave By A Circular Cylinder, James A. Lock, Charles L. Adler

Physics Faculty Publications

We derive the Debye-series expansion of the partial-wave scattering and interior amplitudes for the interaction of a diagonally incident beam of arbitrary profile with an infinitely long homogeneous dielectric circular cylinder. We then discuss the physical interpretation of the various terms of the series. We also consider the one-internal-reflection Debye-series terms for diagonal plane-wave incidence and examine the first-order rainbow extinction transition as a function of the tilt angle of the incident plane wave. We experimentally observe the first-order rainbow extinction transition and compare our observations with the Debye-series predictions. (C) 1997 Optical Society of America.

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Enhanced Coupling To Microsphere Resonances With Optical Fibers, A. Serpengüzel, S. Arnold, G. Griffel, James A. Lock Apr 1997

Enhanced Coupling To Microsphere Resonances With Optical Fibers, A. Serpengüzel, S. Arnold, G. Griffel, James A. Lock

Physics Faculty Publications

Morphology-dependent resonances (MDR's) of polystyrene microspheres were excited by an optical fiber coupler. For optical elimination of the air-cladding interface at the optical fiber coupler surface, the microsphere was immersed in an index-matching oil. MDR's were observed, even though the relative refractive index between the microsphere and the oil was only 1.09. The observed MDR spectra are in good agreement with the generalized Lorenz-Mie theory and the localization principle. The scattering efficiency into each MDR is estimated as a function of the impact parameter by means of generalized Lorenz-Mie theory. (C) 1997 Optical Society of America.

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Bifurcation Of The Equilibrium States Of A Weightless Liquid Bridge, Lev A. Slobozhanin, J. Iwan D. Alexander, Andrew Resnick Mar 1997

Bifurcation Of The Equilibrium States Of A Weightless Liquid Bridge, Lev A. Slobozhanin, J. Iwan D. Alexander, Andrew Resnick

Physics Faculty Publications

The bifurcation of the solutions of the nonlinear equilibrium problem of a weightless liquid bridge with a free surface pinned to the edges of two coaxial equidimensional circular disks is examined. The bifurcation is studied in the neighborhood of the stability boundary for axisymmetric equilibrium states with emphasis on the boundary segment corresponding to nonaxisymmetric critical perturbations. The first approximations for the shapes of the bifurcated equilibrium surfaces are obtained. The stability of the bifurcated states is then determined from the bifurcation structure. Along the maximum volume stability limit, depending on values of the system parameters, loss of stability with …

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Study Of The Crystallization Of Zeolite Naa By Quasi-Elastic Light-Scattering Spectroscopy And Electron Microscopy, Leszek Gora, Kiril A. Streletzky, Robert W. Thompson, George D.J. Phillies Mar 1997

Study Of The Crystallization Of Zeolite Naa By Quasi-Elastic Light-Scattering Spectroscopy And Electron Microscopy, Leszek Gora, Kiril A. Streletzky, Robert W. Thompson, George D.J. Phillies

Physics Faculty Publications

A study of the crystallization of the molecular sieve zeolite NaA from clear aluminosilicate solutions is reported. It was determined by powder X-ray diffraction that zeolite NaA was the only phase in the solid precipitate. The syntheses were monitored in situ by quasi-elastic light scattering spectroscopy. Characteristics of the products were examined by scanning and transmission electron microscopy. Our data show that nuclei formed from the clear aluminosilicate solution, that crystal growth occurred from the solution, that crystal growth was accelerated at elevated temperatures, and that aging the solution at room temperature before raising the synthesis temperature increased both the …

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Thermal Fluctuations In Systems With Continuous Symmetry, Ulrich Zürcher Mar 1997

Thermal Fluctuations In Systems With Continuous Symmetry, Ulrich Zürcher

Physics Faculty Publications

We investigate relaxation and thermal fluctuations in systems with continuous symmetry in arbitrary spatial dimensions. For the scalar order parameter ζ(r, t) with r∈ℛd, the deterministic relaxation is caused by hydrodynamic modes η∂ζ(r, t)/∂t= K∇2ζ(r, t). For a finite volume V, we expand the scalar field in a discrete Fourier series and then we study the behavior in the limit V→∞. We find that the second moment is well defined for dimensions d≥3, while it diverges for d=1, 2. Furthermore, we show that for d<4, the decay of the scalar field does not define an "effective" relaxation time. For dimensions d<4, these two properties suggest scale-invariant properties of the scalar field in the limit V→∞. We show that thermal fluctuations are described by fractional Brownian motion for d ≤ 3 and by ordinary Brownian motion for d ≥ 4. The spectral density of the stochastic force follows 1/f for d=1 and d=2, for d=3, and "white noise," f0 for d≥4. We find explicit representation of the equilibrium distribution of the conserved scalar field. For d≥4 it is a Gaussian distribution, while for d=1 and d=2, it is the Cauchy distribution.

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Scattering Of A Diagonally Incident Focused Gaussian Beam By An Infinitely Long Homogeneous Circular Cylinder, James A. Lock Mar 1997

Scattering Of A Diagonally Incident Focused Gaussian Beam By An Infinitely Long Homogeneous Circular Cylinder, James A. Lock

Physics Faculty Publications

I expand the radiation potential of an arbitrary monochromatic electromagnetic wave in the cylindrical coordinate eigenfunctions of the scalar Helmholtz equation. Since the resulting beam shape coefficients are found to be an inverse Fourier transform of the z component of the beam fields, the incident Gaussian beam is parameterized by a Fourier angular spectrum of plane waves. The beam's partial-wave coefficients are then obtained, as well as the scattered fields produced by the interaction of the beam with an infinitely long homogeneous circular cylinder. The fields are evaluated analytically in the far zone by the method of stationary phase, and …

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Morphology-Dependent Resonances Of An Infinitely Long Circular Cylinder Illuminated By A Diagonally Incident Plane Wave Or A Focused Gaussian Beam, James A. Lock Mar 1997

Morphology-Dependent Resonances Of An Infinitely Long Circular Cylinder Illuminated By A Diagonally Incident Plane Wave Or A Focused Gaussian Beam, James A. Lock

Physics Faculty Publications

The S matrix for scattering a diagonally incident focused Gaussian beam by an infinitely long circular cylinder is calculated, and the diagonal and off-diagonal elements of the matrix are physically interpreted. In addition, the TE and TM morphology-dependent resonances of the cylinder for plane-wave incidence are examined, and it is found that the cylinder size parameter at resonance increases as the angle of incidence of the plane wave increases. The size parameter increase is explained in terms of the heuristic model of morphology-dependent resonances. The presence of both TE and TM resonances in each of the epsilon-polarized and mu-polarized partial-wave …

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An Instantaneous Normal Mode Description Of Relaxation In Supercooled Liquids, T. Keyes, G. V. Vijayadamodar, Ulrich Zurcher Jan 1997

An Instantaneous Normal Mode Description Of Relaxation In Supercooled Liquids, T. Keyes, G. V. Vijayadamodar, Ulrich Zurcher

Physics Faculty Publications

Relaxation in supercooled liquids is formulated from the instantaneous normal modes (INM) point of view. The frequency and temperature dependence of the unstable, imaginary frequency lobe of the INM density of states, ⟨ρu(ω,T)⟩ (for simplicity we write ω instead of iω), is investigated and characterized over a broad temperature range, 10⩾T⩾0.42, in the unit density Lennard-Jones liquid. INM theories of diffusion invoke Im-ω modes descriptive of barrier crossing, but not all imaginary frequency modes fall into this category. There exists a cutoff frequency ωc such that modes with ω<ωc correspond to “shoulder potentials,” whereas the potential profiles include barrier-crossing double wells for ω>ωc. Given that only modes with ω>ωc contribute to diffusion, …

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Plateau Tank Apparatus For The Study Of Liquid Bridges, Andrew Resnick, J. Iwan D. Alexander Jan 1997

Plateau Tank Apparatus For The Study Of Liquid Bridges, Andrew Resnick, J. Iwan D. Alexander

Physics Faculty Publications

An apparatus has been constructed and used to study the equilibrium and dynamical behavior of liquid bridges under reduced effective gravity. Liquid bridges are created and manipulated using six independent computer controlled stepper motors which drive linear motion tables. The bridges are visualized with a high magnification coherent Fourier optical system and in an orthogonal view using incoherent white light. By calibrating a density hydrometer and measuring the interfacial energy between the bridge and bath, reliable Bond numbers as low as 10−4 can be created and held stable for extended periods of time. Dimensional control of the liquid bridges approaches …

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Far-Field Scattering Of A Non-Gaussian Off-Axis Axisymmetric Laser Beam By A Spherical Particle, James A. Lock, Joseph T. Hodges Nov 1996

Far-Field Scattering Of A Non-Gaussian Off-Axis Axisymmetric Laser Beam By A Spherical Particle, James A. Lock, Joseph T. Hodges

Physics Faculty Publications

Experimental laser beam profiles often deviate somewhat from the ideal Gaussian shape of the axisymmetric TEM(00) laser mode. To take these deviations into account when calculating light scattering of an off-axis beam by a spherical particle, we use our phase-modeling method to approximate the beam-shape coefficients in the partial wave expansion of an experimental laser beam. We then use these beam-shape coefficients to compute the near-forward direction scattering of the off-axis beam by the particle. Our results are compared with laboratory data, and we give a physical interpretation of the various features observed in the angular scattering patterns. (C) 1996 …

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An Exactly Soluble Fresnel Diffraction Model Of Two-Slit Interference, James A. Lock Oct 1996

An Exactly Soluble Fresnel Diffraction Model Of Two-Slit Interference, James A. Lock

Physics Faculty Publications

Using the formalism of Fresnel diffraction, we examine the diffraction and interference of two initially widely separated parallel Gaussian light beams. This two-beam configuration is a version of Young's two-slit interference problem that is free of the mathematical complexity that occurs in most Fresnel diffraction calculations. As a result, it clearly and simply illustrates the transition from ray optics to wave interference. (C) 1996 American Association of Physics Teachers.

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Far-Field Scattering Of An Axisymmetric Laser Beam Of Arbitrary Profile By An On-Axis Spherical Particle, James A. Lock, Joseph T. Hodges Jul 1996

Far-Field Scattering Of An Axisymmetric Laser Beam Of Arbitrary Profile By An On-Axis Spherical Particle, James A. Lock, Joseph T. Hodges

Physics Faculty Publications

Experimental laser beam profiles often deviate somewhat from the ideal Gaussian shape of the TEM(00) laser mode. In order to take these deviations into account when calculating light scattering, we propose a method for approximating the beam shape coefficients in the partial wave expansion of an experimental laser beam. We then compute scattering by a single dielectric spherical particle placed on the beam's axis using this method and compare our results to laboratory data. Our model calculations fit the laboratory data well. (C) 1996 Optical Society of America

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Ray Scattering By An Arbitrarily Oriented Spheroid .I. Diffraction And Specular Reflection, James A. Lock Jan 1996

Ray Scattering By An Arbitrarily Oriented Spheroid .I. Diffraction And Specular Reflection, James A. Lock

Physics Faculty Publications

Diffraction and reflection of an arbitrarily polarized plane wave by an arbitrarily oriented spheroid in the short-wavelength limit are considered in the context of ray theory. A closed-form solution for both diffraction and reflection is obtained, and the polarization character of the diffracted plus reflected electric field is obtained. It is found that the magnitude of the reflected electric field is multivalued for forward scattering. This is interpreted in terms of the variation of the spheroid's Gaussian curvature at the points where grazing ray incidence occurs.

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Ray Scattering By An Arbitrarily Oriented Spheroid .Ii. Transmission And Cross-Polarization Effects, James A. Lock Jan 1996

Ray Scattering By An Arbitrarily Oriented Spheroid .Ii. Transmission And Cross-Polarization Effects, James A. Lock

Physics Faculty Publications

Transmission of an arbitrarily polarized plane wave by an arbitrarily oriented spheroid in the short-wavelength limit is considered in the context of ray theory. The transmitted electric field is added to the diffracted plus reflected ray-theory electric field that was previously derived to obtain an approximation to the far-zone scattered intensity in the forward hemisphere. Two different types of cross-polarization effects are found. These are (a) a rotation of the polarization state of the transmitted rays from when they are referenced with respect to their entrance into the spheroid to when they are referenced with respect to their exit from …

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Failure Of The Optical Theorem For Gaussian-Beam Scattering By A Spherical Particle, James A. Lock, Joseph T. Hodges, Gérard Gouesbet Dec 1995

Failure Of The Optical Theorem For Gaussian-Beam Scattering By A Spherical Particle, James A. Lock, Joseph T. Hodges, Gérard Gouesbet

Physics Faculty Publications

It is shown that when an electromagnetic wave with some degree of amplitude rolloff in the transverse direction is scattered by a spherical particle, the optical theorem is not valid. For such shaped beams the extinction cross section may be written as an infinite series in powers of the reciprocal of the beam width. The imaginary part of the forward-scattering amplitude is shown to be the first term in this series. Two approximations to based on the dominance of diffraction in the forward direction for w(0) greater than or similar to a, where w(0) is the beam half-width and a …

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