Showing papers on "Reflection (physics) published in 1999"

Scattering-matrix treatment of patterned multilayer photonic structures

Abstract: We present calculations of surface reflectivity and emission spectra for multilayer dielectric waveguides with a two-dimensional patterning of deep holes. The spectra are obtained using a scattering-matrix treatment to propagate electromagnetic waves through the structure. This treatment incorporates, in a natural way, the extended boundary conditions necessary to describe external reflection and emission processes. The calculated spectra demonstrate how such measurements can be used to obtain experimental information about the waveguide photonic band structure, the coupling of scattering modes to external fields, and the field distribution within the waveguide.

Thickness-profile measurement of transparent thin-film layers by white-light scanning interferometry

Abstract: White-light scanning interferometry is increasingly used for precision profile metrology of engineering surfaces, but its current applications are limited primarily to opaque surfaces with relatively simple optical reflection behavior. A new attempt is made to extend the interferometric method to the thickness-profile measurement of transparent thin-film layers. An extensive frequency-domain analysis of multiple reflection is performed to allow both the top and the bottom interfaces of a thin-film layer to be measured independently at the same time by the nonlinear least-squares technique. This rigorous approach provides not only point-by-point thickness probing but also complete volumetric film profiles digitized in three dimensions.

Correlation between Compton reflection and X-ray slope in Seyferts and X-ray binaries

Abstract: We find a very strong correlation between the intrinsic spectral slope in X-rays and the amount of Compton reflection from a cold medium in Seyfert AGNs and in the hard state of X-ray binaries with either black holes or weakly magnetized neutron stars. Objects with soft intrinsic spectra show much stronger reflection than those with hard spectra. We find that, at a given spectral slope, black hole binaries have similar reflection to or more reflection than Seyferts, whereas neutron star binaries in our sample have reflection consistent with that in Seyferts. The existence of the correlation implies a dominant role of the reflecting medium as a source of seed soft photons for thermal Comptonization in the primary X-ray source.

Converted-wave reflection seismology over inhomogeneous, anisotropic media

Abstract: Converted‐wave processing is more critically dependent on physical assumptions concerning rock velocities than is pure‐mode processing, because not only moveout but also the offset of the imaged point itself depend upon the physical parameters of the medium. Hence, unrealistic assumptions of homogeneity and isotropy are more critical than for pure‐mode propagation, where the image‐point offset is determined geometrically rather than physically. In layered anisotropic media, an effective velocity ratio γeff≡γ22/γ0 (where γ0≡V¯p/V¯s is the ratio of average vertical velocities and γ2 is the corresponding ratio of short‐spread moveout velocities) governs most of the behavior of the conversion‐point offset. These ratios can be constructed from P-wave and converted‐wave data if an approximate correlation is established between corresponding reflection events. Acquisition designs based naively on γ0 instead of γeff can result in suboptimal data collection. Computer programs that implement algorithms for isotropi...

Material level sensor having a wire-horn launcher

Abstract: A single-wire time-domain reflectometer (TDR) combines the best performance features of prior art "electronic dipsticks" in a high accuracy implementation that allows tank penetration though a small opening. A wire-horn structure is employed to launch TDR pulses onto a single wire transmission line, wherein the horn wires can be flexed inwards so the dipstick structure can be inserted through a small tank opening. Once inside the tank, the horn wires flex to their normal state to provide a controlled reference reflection while simultaneously providing high coupling efficiency to the dipstick. The TDR system determines the fill-level of a tank by measuring the time difference between a reflection created at the wire-horn, which all is at the top of a tank, and a reflection from a material in the tank. The TDR employs automatic time-of-peak (TOP) detectors and incorporates a 2-diode sampler, a low-aberration pulse generator, and a 0.001% accurate timebase.

Grazing incidence small angle x-ray scattering from free-standing nanostructures

Abstract: We develop the theory for grazing incidence small-angle x-ray scattering (GISAXS) from nanometer-sized naked islands on a flat substrate in the framework of the distorted-wave Born approximation (DWBA). The scattered wave amplitude is composed of four terms, including all combinations of scattering from the islands and reflection from the substrate. We apply this theory to x-ray measurements on Ge islands grown on Si(111), and show that we can determine the full triangular symmetry of these islands. The results also show that the DWBA must be used for smooth substrates near the angle of total external reflection. We finally discuss the advantages of GISAXS as compared to transmission small angle x-ray scattering for determining the symmetry of nanostructures.

An Elusive Blind-Thrust Fault Beneath Metropolitan Los Angeles

Abstract: Seismic reflection profiles, petroleum wells, and relocated earthquakes reveal the presence of an active blind-thrust fault beneath metropolitan Los Angeles. A segment of this fault likely caused the 1987 Whittier Narrows (magnitude 6.0) earthquake. Mapped sizes of other fault segments suggest that the system is capable of much larger (magnitude 6.5 to 7) and more destructive earthquakes.

Determination of guided and leaky modes in lossless and lossy planar multilayer optical waveguides: reflection pole method and wavevector density method

Abstract: Two numerical methods, the reflection pole method (RPM) and the wavevector density method (WDM), are introduced for determining the propagation constants of guided and leaky modes in lossless and lossy planar multilayer waveguides. These methods are based on the extraction of propagation constants from Lorentzian-type peaks of the reflection coefficient (RPM) or on the density of wavevectors of the structure (WDM). Furthermore, in the case of the RPM the propagation constants can be determined with the help of the phase variation of the denominator of the reflection coefficient in conjunction with an optimization procedure. Both methods are tested on numerically "challenging" multilayer waveguides such as a two-metal-layer waveguide, a multilayer lossy waveguide, and an ARROW waveguide. The results produced by both methods are in good agreement with other numerical techniques but are obtained without the need for solving a dispersion equation in the complex plane. In addition, an approximate but easily implementable method is proposed which verifies whether a cluster of radiation modes can be accurately represented by a single leaky mode.

Light-emitting diodes with 31% external quantum efficiency by outcoupling of lateral waveguide modes

Abstract: The external quantum efficiency of light-emitting diodes (LEDs) is usually limited by total internal reflection at the semiconductor–air interface. This problem can be overcome by a combination of light scattering at a textured top surface and reflection on a backside mirror. With this design, we achieve 22% external quantum efficiency. One of the main loss mechanisms in such nonresonant cavity (NRC) light-emitting diodes is coupling into an internal waveguide. Texturing the surface of this waveguide allows the partial extraction of the confined light. In this way, we demonstrate an increase in the external quantum efficiency of NRC-LEDs to 31%.

Ocean waves and ice sheets

Abstract: A complete analytical study is presented of the reflection and transmission of surface gravity waves incident on ice-covered ocean. The ice cover is idealized as a plate of elastic material for which flexural motions are described by the Timoshenko–Mindlin equation. A suitable non-dimensionalization extracts parameters useful for the characterization of ocean-wave and ice-sheet interactions, and for scaled laboratory studies. The scattering problem is simplified using Fourier transforms and the Wiener–Hopf technique; the solution is eventually written down in terms of some easily evaluated quadratures. An important feature of this solution is that the physical conditions at the edge of the ice sheet are explicitly built into the analysis, and power-flow theorems provide verification of the results. Asymptotic results for large and small values of the non-dimensional parameters are extracted and approximations are given for general parameter values.

Dynamic Response and Wave Propagation in Plane Trusses and Frames

Abstract: The dynamics of planar frames and trusses is analyzed in terms of the propagation of axial (longitudinal) and flexural (transverse) stress waves being structural members. The waves are multiscattered at the joints, and scattering coefficients representing the reflection and transmission of both types of waves at each joint are derived from the dynamics and compatibility conditions of the joint. The complex multireflected waves within the structure are evaluated in the frequency domain by a newly developed reverberation matrix, which is formulated from scattering coefficients and propagating phase factors. Transient waves are then analyzed by Fourier synthesis and evaluated by a fast Fourier transform algorithm. Transient responses for the axial and bending strains in all structural members are calculated over a long duration for a model truss with rigid joints. Comparison to experimental data of the model truss under a step loading shows good agreement for the early as well as considerably long time responses.

Experimental measurement of the effect of termination on surface electromagnetic waves in one-dimensional photonic bandgap arrays

Abstract: Two different attenuated total-internal reflection prism configurations are used to explore the excitation of surface electromagnetic waves on one-dimensional (1-D) photonic bandgap (PBG) arrays. The effect of surface termination of the photonic crystal is shown to have a significant effect on the dispersion of the surface modes excited at that interface. The results show that it is possible to engineer the position of the surface mode within the forbidden bandgap. Modes that are located close to the center of the bandgap are shown to be more localized, leading to significantly higher surface electromagnetic fields than modes located near the band edge. The existence of surface modes can have an effect on many of the proposed applications for PBG materials. The modes are also of interest in their own right for use in applications such as sensors and modulators.

Near critical reflection of internal waves

Abstract: Using a matched asymptotic expansion we analyse the two-dimensional, near-critical reflection of a weakly nonlinear internal gravity wave from a sloping boundary in a uniformly stratified fluid. Taking a distinguished limit in which the amplitude of the incident wave, the dissipation, and the departure from criticality are all small, we obtain a reduced description of the dynamics. This simplification shows how either dissipation or transience heals the singularity which is presented by the solution of Phillips (1966) in the precisely critical case. In the inviscid critical case, an explicit solution of the initial value problem shows that the buoyancy perturbation and the alongslope velocity both grow linearly with time, while the scale of the reflected disturbance is reduced as 1/t. During the course of this scale reduction, the stratification is 'overturned' and the Miles-Howard condition for stratified shear flow stability is violated. However, for all slope angles, the 'overturning' occurs before the Miles-Howard stability condition is violated and so we argue that the first instability is convective. Solutions of the simplified dynamics resemble certain experimental visualizations of the reflection process. In particular, the buoyancy field computed from the analytic solution is in good agreement with visualizations reported by Thorpe & Haines (1987). One curious aspect of the weakly nonlinear theory is that the final reduced description is a linear equation (at the solvability order in the expansion all of the apparently resonant nonlinear contributions cancel amongst themselves). However, the reconstructed fields do contain nonlinearly driven second harmonics which are responsible for an important symmetry breaking in which alternate vortices differ in strength and size from their immediate neighbours.

A theoretical study of duct noise control by flexible panels

Abstract: Theoretical exploration is undertaken for passive noise control by flush-mounted panels in an otherwise rigid duct. For a plane sound wave traveling in the flexible segment, the wall compliance renders a wave speed less than the isentropic speed of sound in air. Scattering and reflection occur at the upstream edge of the panel while the energy flux of the transmitted wave is partitioned between the wall flexural waves and the sound in air. For a lossless panel these waves are scattered and reflected again by the downstream edge forming standing waves responsible for the undesirable passbands. For panels with substantial structural damping, however, both flexural and sound waves diminish with distance, eliminating the passbands. It is estimated that the wave dissipation by panel materials like rubber could outperform typical fibrous duct lining. The combination of wave reflection, dissipation, and slowing down allows broadband, low-frequency noise reduction over a short distance.

Evanescent waves in PML's: origin of the numerical reflection in wave-structure interaction problems

Abstract: The theory of general evanescent waves in perfectly matched layers (PMLs) is presented, both in a continuous medium and in a discretized finite-difference medium. It is shown that evanescent waves may be strongly reflected from vacuum-PML interfaces in the discretized case. This allows the numerical reflection observed in wave-structure interaction problems to be interpreted as the reflection of evanescent fields surrounding the structures.

Method of estimating elastic and compositional parameters from seismic and echo-acoustic data

Abstract: A method for determining from measured reflection data on a plurality of trace positions, a plurality of subsurface parameters. The method includes the steps of: preprocessing the measured reflection data into a plurality of partial or full stacks; specifying one or more initial subsurface parameters defining an initial subsurface model; specifying a wavelet or wavelet field for each of the partial or full stacks of the measured reflection data; calculating synthetic reflection data based on the specified wavelets and the initial subsurface parameters; optimizing an objective function, including the weighted difference between measured reflection data and synthetic reflection data for a plurality of trace positions simultaneously; and outputting the optimized subsurface parameters. A device for implementing this method is also included.

Head-mounted video display device

Abstract: PROBLEM TO BE SOLVED: To provide an inexpensive, light-weight, and small-sized video display device to be mounted on a head. SOLUTION: The device is provided with a single liquid crystal panel 1 on which a two-dimensional picture is displayed, a cross prism 2 which separates a luminous flux emitted from the liquid crystal panel 1 to the right and the left in the horizontal direction by semi-translucent faces 2L and 2R, and a pair of left and right eyepiece optical systems 3L and 3R which transmits separated luminous fluxes to left and right eyes EL and ER of an observer to display the two-dimensional picture as a virtual image. Each of eyepiece optical systems 3L and 3R has a first refracting face S1, a first reflection face S2, a second reflection face S3, and a second refracting face S4 in order from the observer's eye EL or ER. The first refracting face S1 and the second reflection face S3 are made of the same continuous optical face and function as the first refracting face S1 for an incident luminous flux which doesn't satisfy a total reflection condition, and function as the second reflection face S3 for an incident luminous flux satisfying the total reflection condition.

Bragg reflectors for cylindrical waves

Abstract: A transfer matrix method is developed to calculate the electromagnetic field in a dielectric structure with circular cylindrical symmetry. The equations for the reflection and transmission coefficients of cylindrical waves from a single cylindrical boundary between two dielectrics and from a cylindrical multilayered structure are obtained. For a single dielectric interface, enhanced reflection at small interface radii and the analogue of the Brewster effect are predicted and investigated. The design of an optimized cylindrical Bragg reflector (CBR) for cylindrical waves is proposed and its optical properties are studied. It is found that the thicknesses of the layers in the CBR must be different, to provide the adjustment of the phase of the waves, that are reflected from the interfaces at different radii.

Seismic attributes for monitoring of a shallow heated heavy oil reservoir; a case study

Abstract: In production geophysics, detecting the zones of production or constraining the in-situ conditions within a reservoir are often of greater importance than obtaining highly resolved seismic structural images. Standard seismic data processing distorts the signal and limits the potential for extracting additional information, especially for shallow targets. An alternative “shift-stack” procedure is applied in the processing of a shallow 12-fold, 1-m common midpoint (CMP) spacing reflection profile acquired over a heated Athabasca heavy oil sand reservoir. The shift-stack involves summing of CMP traces which have been flattened to an appropriate reference event. Simple modeling confirms that the prestack waveforms are better preserved by this process. Amplitude and frequency attributes are extracted from the reflection profile. Amplitudes of a continuous reservoir event vary by 600% over 35-m intervals along the profile. Bright spots correlate with heated regions. Apparent frequencies, as measured by the instantaneous frequency and by short time-window power spectral estimates of the subreservoir event are 20‐30 Hz lower in these same regions. These diminished apparent frequencies most probably result from interference of the subreservoir reflection with events related to structural changes within the reservoir. A complete interpretation of the results has not been attempted as knowledge of the in-situ conditions is incomplete. However, changes in the seismic response at the well locations suggest that these attributes are useful in detection and mapping of heated zones. The shiftstack procedure may also be useful in environmental and geotechnical applications.

Seismic facies and regional architecture of the Oak Ridges Moraine area, southern Ontario

Abstract: Analysis of over 50 line-kilometres of land-based, shallow, seismic reflection profiles has provided a means of investigating the subsurface architecture and stratigraphic relationships of the glac...

Reflection type liquid crystal display device

Abstract: A reflector electrode is provided with hills and valleys thereon, and the reflector electrode is formed on an inside face of a transparent substrate having a transparent electrode and an opposite substrate. Light-scattering-liquid-crystal is provided with forward-scattering component and back-scattering component, so that scattering of reflected light from the reflector electrode is increased when the light-scattering-liquid-crystal is transparent. As a result, contrast is less dependent on a viewing angle, and a brighter quality display with higher color purity can be obtained.

Diffuse waves in complex media

Abstract: Preface. List of participants. Picture. Localization of waves B. Van Tiggelen. Mathematical theory of localization J. Lacroix. Localization of light in randomized periodic media A. Klein. Photonic band gap materials C. Soukoulis. High-contrast photonic crystals A. Figotin. Photon statistics of a random laser C. Beenakker. Spectra of large random matrices: a method of study E. Kanzieper, V. Freilikher. Optics of ordered and disordered atomic media R. Loudon. Cold atoms and multiple scattering R. Kaiser. Wave scattering from rough surfaces M. Nieto-Vesperinas, A. Madrazo. Acoustic pulses propagating in randomly layered media J.P. Fouque. Reflection and transmission of acoustic weaves by a locally-layered random slab W. Kholer, et al. Seismic wave diffusion in the earth lithosphere M. Campillo, et al. Imaging and averaging in complex media R. Snieder. Subject index.

Determination of Kubelka-Munk scattering and absorption coefficients by diffuse illumination.

Abstract: The Kubelka-Munk theory, although it provides an equation that relates the reflection of a sample under diffuse illumination to certain of its properties, does not take boundary reflectance into account Boundary reflection is always present because there is always a difference between the refractive indices of the sample and of the surrounding medium We describe how a half-sphere is used to achieve diffuse illumination, and we present and exemplify equations that correct for boundary reflection with measurements of four composite restorative dental materials The refractive index of the sample is measured with a matching technique that employs a glycerol-water mixture Edge loss errors are estimated

Analytical and experimental investigations of the reflection of asymmetric shock waves in steady flows

Abstract: The reflection of asymmetric shock waves in steady flows is studied both theoretically and experimentally. While the analytical model was two-dimensional, three-dimensional edge effects influenced the experiments. In addition to regular and Mach reflection wave configurations, an inverse-Mach reflection wave configuration, which has been observed so far only in unsteady flows (e.g. shock wave reflection over concave surfaces or over double wedges) has been recorded. A hysteresis phenomenon similar to the one that exists in the reflection of symmetric shock waves has been found to also exist in the reflection of asymmetric shock waves. The domains and transition boundaries of the various types of overall reflection wave configurations are analytically predicted.

Permittivity determination using amplitudes of transmission and reflection coefficients at microwave frequency

Abstract: A new method is proposed in this paper to determine the permittivity of materials. The general consideration is to use only the amplitudes of the transmission and reflection coefficients to do the permittivity determination. According to the analysis, the permittivity can be uniquely determined by measuring these two amplitudes when a sample is prepared with large enough attenuation that the multiple reflections between the two surfaces of the sample can be neglected. The validity of the method was proven by experiments. Using the method, the instantaneous and noncontacting measurements of the amplitudes can be realized. Thus, the dynamic measurement of the permittivity becomes possible.

Electron acceleration to ultrarelativistic energies in a collisionless oblique shock wave

Abstract: Electron motion in an oblique shock wave is studied by means of a one-dimensional, relativistic, electromagnetic, particle simulation code with full ion and electron dynamics. It is found that an oblique shock can produce electrons with ultrarelativistic energies; Lorentz factors with γ≳100 have been observed in our simulations. The physical mechanisms for the reflection and acceleration are discussed, and the maximum energy is estimated. If the electron reflection occurs near the end of a large-amplitude pulse, those particles will then be trapped in the pulse and gain a great deal of energy. The theory predicts that the electron energies can become especially high at certain propagation angles. This is verified by the simulations.

Pyramidal fly-eye detection antenna for optical wireless systems

Abstract: A novel, pyramidal fly-eye diversity configuration is presented for wireless communication in small and middle-sized office rooms. It is demonstrated that the configuration combats multipath dispersion and increases the received power level in a semi-disperse environment. Since the number of photodetectors in the configuration is limited, the penalty paid for an increase in performance is a limited increase in complexity. A new computation method, based on the reflection properties of plaster walls, is derived for an accurate calculation of the diverse detected pulse response. Pulse responses at various locations within a test room are displayed, both for a single photodetector and the pyramidal fly-eye receiver.

The Generation of Alongslope Currents by Breaking Internal Waves

Abstract: Internal gravity waves propagating in a fluid of constant buoyancy frequency and approaching a uniform sloping boundary from a direction that is not in a plane normal to the boundary, and dissipating energy on reflection, generate alongslope currents. The net radiation stress or momentum flux into the breaking region is proportional to the flux of energy lost from the waves. It is supposed that the stress is balanced by a frictional boundary stress so that a steady alongslope current is generated. The dependence of the strength of the current on the steepness, AIMI, of the incident wave and on its propagation direction is examined as a function of α and β, the inclination of the boundary to the horizontal and the angle between the incident wave group velocity vector and the horizontal, respectively. Alongslope currents of several centimeters per second, generally exceeding the Lagrangian drift produced by wave reflection alone, may be generated in the ocean or in lakes. Reflection of subcritical ...

Reflection type semiconductor display device having optical fiber adjacent the surface of the main body

Abstract: A reflection type semiconductor display device which can make satisfactory display even when external light is not satisfactorily intense is provided. A reflection type semiconductor display device according to the present invention can take in light other than incident light on a liquid crystal panel to be an auxiliary light source using optical fibers, and thus, display of high quality level can be made even indoors or in a place where light is faint. Further, by combining the semiconductor display device with a front light, insufficient amount of light can be supplemented with the front light.

Off-beam lidar: an emerging technique in cloud remote sensing based on radiative green-function theory in the diffusion domain

Abstract: Atmospheric lidars do not penetrate directly most boundary-layer clouds due to their large optical density. However, the lidar's photons are not absorbed but scattered out of the beam. Typically, about half are actually transmitted through the cloud and the other half escape the cloud by reflection in extended diffuse patterns that evolve in time. For all practical purposes, these are the cloud's space-time Green functions (GFs). In a Fourier-Laplace expansion of the space-time GF, the leading term is representative of solar remote-sensing (i.e., steady/uniform source) while higher-order terms correspond to active approaches with temporal- and/or spatial- resolution capabilities. Radiative GF theory is tractable within the limits of photon-diffusion theory and homogeneous clouds. Monte Carlo simulations with realistically variable cloud models are used to extend the range of validity of analytical GF theory with minor modifications. GF theory tells us that physical and optical cloud thicknesses can be retrieved from off-beam cloud lidar returns.