Showing papers on "Reflection (physics) published in 1992"

Theory for off-specular reflection from roughened surfaces

Abstract: The directional distribution of radiant flux reflected from roughened surfaces is analyzed on the basis of geometrical optics. The analytical model assumes that the surface consists of small, randomly disposed, mirror-like facets. Specular reflection from these facets plus a diffuse component due to multiple reflections and/or internal scattering are postulated as the basic mechanisms of the reflection process. The effects of shadowing and masking of facets by adjacent facets are included in the analysis. The angular distributions of reflected flux predicted by the analysis are in very good agreement with experiment for both metallic and nonmetallic surfaces. Moreover, the analysis successfully predicts the off-specular maxima in the reflection distribution which are observed experimentally and which emerge as the incidence angle increases. The model thus affords a rational explanation for the off-specular peak phenomenon in terms of mutual masking and shadowing of mirror-like, specularly reflecting surface facets.

Waves in plasmas

Abstract: Wave normal surfaces waves in a cold uniform plasma causality, acoustic waves and simple drift waves energy flow and accessibility Kruskal-Schwarzschild solutions for a bounded plasma oscillations in bonded plasmas plasma models with discrete structure longitudinal oscillations in a plasma of continuous structure absolute and convective instability susceptibilities for a hot plasma in a magnetic field waves in magnetized uniform media effects on waves from weak collisions reflection, absorption and mode conversion nonuniform plasmas the straight-trajectory approximation quasilinear diffusion quasilinear diffusion in a magnetized plasma bounce-averaged quasilinear diffusion in a magnetized plasma bounce-averaged quasilinear diffusion.

Shock wave reflection phenomena

Abstract: This text describes shock wave reflection phenomena from a phenomenological point of view Organized in five parts, the book covers an introduction to oblique shock wave reflection and the governing equations of the two- and three-shock theories; shock wave reflection in pseudo-steady flows; and reflection phenomena in steady flows and unsteady flows With regard to pseudo-steady, steady and unsteady flows, the possible types of specific reflections are described, criteria for their formation and termination are presented and their governing equations are solved analytically and graphically and compared with experimental results Modification of the governing equations by accounting for viscous and real gas effects are suggested In addition, unresolved problems are pointed out and ideas for future research are suggested The fifth part of the book constitutes a detailed source list of most of the scientific papers and reports which have been published in the subject area

Reflection tomography in the postmigrated domain

Abstract: Reflection tomography is an inversion method that adjusts a velocity and reflector depth model to be consistent with the prestack time data. This tomography approach minimizes the misfit of the data and model in the premigrated domain. Generally, the data are represented by the traveltimes of reflection events, which has made the technique problematic and unpopular. Techniques generally known as “migration velocity analysis” have a similar objective but use the postmigrated domain. For a variety of practical reasons, this postmigrated domain has advantages over the premigrated domain. With slight modifications, the reflection tomography approach can be implemented in the postmigrated domain. In this domain, a model is determined by optimizing the consistency of imaged reflection events on what has been called a common reflection point (CRP) gather. Extending reflection tomography to the postmigrated domain allows much of the knowledge developed for migration velocity analysis to be coupled with that of re...

Analytic expressions for the reflection delay, penetration depth, and absorptance of quarter-wave dielectric mirrors

Abstract: The authors analyze the operation of high-reflectivity quarter-wave (QW) dielectric mirrors at the band-stop center (Bragg) frequency, relevant for the design of small-cavity optoelectronic structures. The energy penetration depth concept is used to determine a first-order linear approximation for the reduction of the mirror peak reflectivity of the QE mirror as a function of the mirror material parameters and the number of layers. The expression can be applied in the limit of small loss. The mathematical analysis and expressions for the absorptance and the peak reflectivity of a dielectric mirror with weak material absorption are presented. The use of the results is illustrated for a typical vertical cavity surface-emitting laser structure. >

Polarization-based material classification from specular reflection

Abstract: A computationally simple yet powerful method for distinguishing metal and dielectric material surfaces from the polarization characteristics of specularly reflected light is introduced. The method is completely passive, requiring only the sensing of transmitted radiance of reflected light through a polarizing filter positioned in multiple orientations in front of a camera sensor. Precise positioning of lighting is not required. An advantage of using a polarization-based method for material classification is its immunity to color variations, which so commonly exist on uniform material samples. A simple polarization-reflectance model, called the Fresnel reflectance model, is developed. The fundamental assumptions are that the diffuse component of reflection is completely unpolarized and that the polarization state of the specular component of reflection is dictated by the Fresnel reflection coefficients. The material classification method presented results axiomatically from the Fresnel reflectance model, by estimating the polarization Fresnel ratio. No assumptions are required about the functional form of the diffuse and specular components of reflection. The method is demonstrated on some common objects consisting of metal and dielectric parts. >

Transmission/reflection and short-circuit line methods for measuring permittivity and permeability

Abstract: The transmission/reflection and short-circuit line methods for measuring complex permittivity and permeability of materials in waveguides and coaxial lines are examined. Equations for complex permittivity and permeability are developed from first principles. In addition, new formulations for the determination of complex permittivity and permeability independent of reference plane position are derived. For the one-sample transmission/reflection method and two-position short-circuit line measurements, the solutions are unstable at frequencies corresponding to integral multiples of one-half wavelength in the sample. For two-sample methods ttie solutions are unstable for frequencies where both samples resonate simultaneously. Criteria are given for sample lengths to maintain stability. An optimized solution is also presented for the scattering parameters. This solution is stable over all frequencies and is capable of reducing scattering parameter data on materials with higher dielectric constant. An uncertainty analysis for the various techniques is developed and the results are compared. The errors incurred due to the uncertainty in scattering parameters, length measurement, and reference plane position are used as inputs to the uncertainty models.

Borehole radar applied to the characterization of hydraulically conductive fracture zones in crystalline rock1

Abstract: This paper discusses the borehole radar system, RAMAC, developed within the framework of the International Stripa Project, which can be used in three different measuring modes; single-hole reflection, cross-hole reflection and cross-hole tomography. The reflection modes basically provide geometrical data on features located at some distance from the borehole. In addition the strength of the reflections indicate the contrast in electrical properties. Single-hole reflection data are cylindrically symmetrical with respect to the borehole, which means that a unique fracture orientation cannot be obtained. A method has been devised where absolute orientation of fracture zones is obtained by combining single-hole reflection data from adjacent holes. Similar methods for the analysis of cross-hole reflection data have also been developed and found to be efficient. The radar operates in the frequency range 20-60 MHz which gives a resolution of 1-3 m in crystalline rock. The investigation range obtained in the Stripa granite is approximately 100 m in the single-hole mode and 200-300 m in the cross-hole model. Variations in the arrival time and amplitude of the direct wave between transmitter and receiver have been used for cross-hole tomographic imaging to yield maps of radar velocity and attenuation. The cross-hole measurement configuration coupled withmore » tomographic inversion has less resolution than the reflection methods but provides better quantitative estimates of the values of measured properties. The analysis of the radar data has provided a consistent description of the fracture zones at the Stripa Cross-hole site in agreement with both geological and geophysical observations.« less

Quantum waveguide theory for mesoscopic structures.

Abstract: A one-dimensional quantum waveguide theory for mesoscopic structures is proposed, and the boundary conditions of the wave functions at an intersection are given. The Aharonov-Bohm effect is quantitatively discussed with use of this theory, and the reflection, transmission amplitudes, etc., are given as functions of the magnetic flux, the arm lengths, and the wave vector. It is found that the oscillating current consists of a significant component of the second harmonic. This theory is also applied to investigate quantum-interference devices. The results on the Aharonov-Bohm effect and the quantum-interference devices are found to be in agreement with previous theoretical results.

Scattering of electromagnetic waves by periodic structures

Abstract: The authors consider periodic structures made of spheres embedded in a host material with a different dielectric function. They show how to calculate the reflection and transmission of electromagnetic waves by a slab of the material parallel to a given crystallographic plane. The method of calculation is based on a doubling-layer scheme which obtains the reflection and transmission matrix elements for the multilayer from those of a single layer. The reflection and transmission characteristics of the slab are related to the complex band structure of the photon field associated with the given crystallographic plane of the corresponding infinite crystal, which is introduced in the manner of the low-energy electron diffraction theory. They present numerical results which demonstrate the applicability of the method to real systems of current interest and point out some interesting physics which arose from their calculations. They show in particular that the nondegenerate bands of the photon field at the centre of the surface Brillouin zone do not couple to the incident radiation, leading to total reflection at normal incidence.

Optical Guided Waves and Devices

Abstract: Overview electromagnetic fields and plane waves material effects the optics of beams reflection and refraction at a single interface the slab waveguide planar waveguide integrated optics optical fibres and fibre devices coupled mode devices optoelectronic interactions in semiconductors optoelectronic devices optic device fabrication systems and applications.

Time delay of evanescent electromagnetic waves and the analogy to particle tunneling.

Abstract: The analogy between quantum tunneling of particles and evanescent electromagnetic waves can be used to study particle tunneling. Possibilities for the measurement of the time delay resulting from the transmission of waves through an evanescent region, say with lower dielectric constant, are discussed. In contrast to particle tunneling, an electromagnetic pulse can consist of many photons and can be probed in a noninvasive way. We emphasize the delay of the centroid of an electromagnetic pulse transmitted below cutoff through a portion of a waveguide with the same cross section as the adjacent propagating guides. The boundary conditions at the interface between the propagating and the evanescent region lead to the same transmission and reflection coefficients as for a square-barrier tunneling problem. For a pulse restricted to a narrow frequency range, the time delay depends only on the frequency derivative of the phase shift associated with transmission. The delay of a centroid is just that; there is no deeper physical sense which links the incoming centroid to the outgoing centroid. For sufficiently long evanescent regions, the delay is independent of thickness.

Tandem resonator reflectance modulator

Abstract: A wide band optical modulator is grown on a substrate as tandem Fabry-Perot resonators including three mirrors spaced by two cavities. The absorption of one cavity is changed relative to the absorption of the other cavity by an applied electric field, to cause a change in total reflected light, as light reflecting from the outer mirrors is in phase and light reflecting from the inner mirror is out of phase with light from the outer mirrors.

Higher-order bragg reflection of gravity surface waves by periodic beds

Abstract: Experiments are described which demonstrate higher-order Bragg resonant interactions between linear gravity waves and doubly sinusoidal beds. These higher-order effects, which include harmonic and subharmonic Bragg reflections, have been observed by making very precise measurements in a wave tank. Subharmonic reflection was found to be very large, even for small bottom undulation amplitudes. The experimental data are compared with the predictions of a numerical model based on the full potential theory of linear waves.

Reflection and transmission of waves by a complex potential—a semiclassical Jeffreys–Wentzel–Kramers–Brillouin treatment

Abstract: In this paper, the reflection and transmission of plane waves are examined from a complex potential. Such potentials have the property of absorbing wave packets incident on them and are used widely in time‐dependent quantum scattering theory. The purpose of the study is to determine the optimal form of potential to be used for absorbing wave packets near the edges of finite grids in coordinate space. The best potentials for such purposes lead to the minimum possible transmission and reflection of the incident wave packet. The Jeffreys–Wentzel–Kramers–Brillouin (JWKB) theory is used to address this problem and a new form for the optimal complex potential is proposed. A scaled dimensionless form of the Schrodinger equation is also derived, so that the parameters of any optimized potential obtained for a particular collision energy and mass combination may be readily converted to apply to a new set of masses and energies.

Grin type diffuser based on volume holographic material

Abstract: A diffuser based on a phase volume holographic medium is recorded non-holographically with speckle which define non-discontinuous and smoothly varying change in the refractive index of the medium. The diffuser scatters light traveling from an entrance surface to an exit surfaces and reflection from the diffuser is substantially limited to Fresnel reflection from the entrance and exit surfaces and light exiting the exit surface is substantially non-specular.

Interaction of electromagnetic waves with general bianisotropic slabs

Abstract: An efficient, elegant, and systematic formulation technique which, combining Fourier transform with matrix analysis methods, is suitable for problems related to radiation by dipole or other sources in the presence of an arbitrarily general stratified anisotropic medium has been recently developed. This technique is adapted further extended to allow the presence of general bianisotropic media described by four tensors with no limitations on their elements. Two specific applications pertaining to some canonical problems of fundamental importance are included to exemplify the method and demonstrate its usefulness: radiation by an arbitrarily oriented elementary electric dipole source located in the vicinity of a general bianisotropic slab, either grounded or ungrounded, leading to the expressions of the dyadic Green's function of the structure, and reflection and transmission of an arbitrarily polarized plane wave incident upon such a slab, leading to closed-form concise expressions for the reflection and transmission coefficient matrices. >

Imaging salt with turning seismic waves

Abstract: Turning seismic waves, which first travel downward and then upward before (and after) reflection, have been recorded in a 3-D seismic survey conducted over an overhanging salt dome. Careful processing of these turning waves enables the imaging of the underside of the salt dome and of intrusions of salt into vertical faults radiating from the dome.When seismic wave velocity increases with depth, waves that initially travel downward are reflected and may turn so as to travel upward before reflection. A simple geometrical argument suggests that these turning waves are likely to exhibit abnormal moveout in com-mon-midpoint (CMP) gathers, in that reflection time decreases with increasing source-receiver offset. This abnormal moveout and the attenuation of turning waves by most migration methods suggest that conventional seismic processing does not properly image turning waves.The most important step in imaging turning waves, assuming that they have been recorded, is the migration process. Simple and inexpensive modifications to the conventional phase-shift migration method enable turning waves to be imaged for little additional computational cost. The examples provided in this paper suggest that these and other such modifications to conventional processing should be used routinely when imaging salt domes.

Confocal optical scanner

Abstract: A confocal optical scanner of Nipkow disk type for measuring a sample, in which each component of two or more color pigments, has a high reflection mirror for separating an excited light to be radiated onto the sample and a fluorescence emitted from the sample, wherein a reflectance of the high reflection mirror is from 80% to 100% in a measured wavelength region including at least an excited light wavelength region and a fluorescence wavelength region. Thereby, the confocal optical scanner capable of measuring a polychromatic fluorescent image at the same time is realized with the enhanced light receiving efficiency of fluorescence, using one high reflection mirror without using a plurality of dichroic mirrors by exchange.

A robust transfer matrix formulation for the ultrasonic response of multilayered absorbing media

Abstract: An improved version of the transfer matrix approach is presented for ultrasonic wave interaction in multilayered media. Generalized expressions are obtained for reflection and transmission coefficients in either fluid or solid half‐space and problems associated with numerical stability are solved efficiently. The formulation is applicable to longitudinal and shear input waves alike, at arbitrary incidence angles and for any sequence of solid or fluid layers. Also, allowance is made for viscoelastic behavior by means of relaxation functions in the Laplace transform domain. Finally, the response to arbitrary incident pulse shapes and beam profiles is described through application of two‐dimensional numerical Laplace inversion.

Plane‐wave reflection and transmission coefficients for a transversely isotropic solid

Abstract: Numerous investigators have studied the P-SV reflection and transmission coefficients of an isotropic solid (Zoeppritz, 1919; Nafe, 1957; Frasier, 1970; Young and Braile, 1976; Kind, 1976; Aki and Richards, 1980).

Detection of specularity using colour and multiple views

Abstract: This paper presents a model and an algorithm for the detection of specularities from Lambertian reflections using multiple color images from different viewing directions. The algorithm, called spectral differencing, is based on the Lambertian consistency that color image irradiance from Lambertian reflection at an object surface does not change depending on viewing directions, but color image irradiance from specular reflection or from a mixture of Lambertian and specular reflections does change. The spectral differencing is a pixelwise parallel algorithm, and it detects specularities by color differences between a small number of images without using any feature correspondence or image segmentation. Applicable objects include uniformly or nonuniformly colored dielectrics and metals, under extended and multiply colored scene illumination. Experimental results agree with the model, and the algorithm performs well within the limitations discussed.

One-dimensional modeling of the wavelength sensitivity, localization, and correlation in reflectometry measurements of plasma fluctuations

Abstract: The reflection of electromagnetic waves from a plasma cutoff layer has been used to examine properties of density fluctuations in fusion plasmas. In this paper an exact one‐dimensional model is used to show the relation between changes in the phase of the reflected wave and the location, magnitude, and correlation properties of density fluctuations. For long‐wavelength density perturbations the reflected phase can be simply related to the amplitude of fluctuating density and the density scale length, Ln, near the cutoff layer. However, the phase response falls substantially as the fluctuation wavelength approaches the free space wavelength of the reflected wave, λ0, and the location of the maximum response moves out in front of the cutoff layer following the wave matching condition kΛ= 2k ≊ 2η(x)k0. Thus, a measurement of the reflected phase is strongly weighted to and localized for phenomena whose wavelength is longer than the characteristic scale (λ20Ln)1/3. Because of this weighting and because the region of maximum response moves away from the cutoff layer for short‐wavelength fluctuations, there is also a limitation in any estimate of the density correlation length from the reflected phase. The correlation of phases between several different probe frequencies can be used to estimate a density correlation length no less than about four times the free space probe wavelength.

Reflection and transmission coefficients in fluid‐saturated porous media

Abstract: Using Biot’s theory to describe the propagation of elastic waves in a fluid‐saturated porous elastic solid (a Biot medium), the reflection and transmission coefficients were computed at a plane interface between a fluid and a Biot medium and at interfaces inside a Biot medium defined by either a change in saturant fluids or in the intrinsic rock permeability. The reflection and transmission coefficients were computed with and without the inclusion of a frequency correction factor that according to Biot has to be introduced in the equations above a certain critical frequency (‘‘frequency‐dependent’’ versus ‘‘classic model’’). For a fluid–Biot medium interface and in the range 5 kHz–10 MHz for the example analyzed the two models show differences of the order of 11% for the reflection coefficients and between 11% and 31% for the type I, type II, and shear transmission coefficients. For the interfaces within a Biot medium, and for type II incident waves, in the same range of frequencies the cases examined sho...

Bragg reflectors

Abstract: A Bragg reflector composed of periodic cylindrically symmetric corrugations can provide a reflection of nearly unity through the principles of constructive interference, allowing the formation of a frequency selective resonator. Mode conversion will occur, but can be reduced by tapering the amplitude of the corrugations. Reflection measurements are compared with theoretical predictions for untapered sinusoidal and rectangular corrugation as well as a reflector tapered according to the Hamming-window prescription. Measurements of Bragg resonators are also presented. >

Wave flume experiments on two-dimensional oscillating water column wave energy devices

Abstract: Experiments were performed in a wave flume with regular waves of very small amplitude-to-wavelength ratio (less than 0.01). Their purpose was mainly the validation of the oscillating surface pressure theory of Sarmento and Falcao (1985) applied to wave energy absorption by oscillating water column (OWC) devices. Experimental and theoretical curves for the efficiency and for the reflection and transmission coefficients were obtained and compared. The test also included the validation of the two-wave-gauge experimental procedure used to decouple direct and reflected wave trains, as well as the effects of increasing the depth of immersion of the OWC overhang on the efficiency-wave period curves.