Showing papers on "Reflection (physics) published in 2001"

Chapter 4 - Singular optics

Abstract: Singular optics is a branch of modern physical optics that involves a wide class of effects associated with the phase singularities in wave fields and with the topology of wave fronts. Optical singularities (optical vortices) exhibit some fundamental features absent in the "usual" fields with smooth wave fronts. Namely, optical vortices possess orbital angular momentum, topological charge for helical wave front of beams with well-defined direction of propagation. As a result, an interesting spatial evolution can be generated such as optical vortices "nucleation" and "annihilation" by pairs with participation of phase saddles, often called "optical chemistry." To study the structure of the circular edge dislocation, an isolated dark (zero-amplitude) ring is created within a light beam, with an analytical description of the field. A screw wave-front dislocation has a feature that the spatial structure of the wave front has the form of a helicoid around the dislocation axis. The chapter also describes reflection, refraction, interference and diffraction of OVs. Both frequency up- and down-conversion processes possess essential peculiarities for light beams with OVs. The chapter discusses the topology of wave fronts and vortex trajectories. Gouy phase shift in singular optics is also described in the chapter.

Dynamical theory of x-ray diffraction

Abstract: This chapter presents the dynamical theory of the diffraction of X-rays by perfect crystals. The most important part is devoted to the case of plane waves (Section 5.1.2). The solutions of the propagation equation of plane waves in crystals are given in Section 5.1.3 using the concept of wavefields introduced by Ewald for X-rays in 1913 and by Bloch for electrons in 1928 (known in solid-state physics as Bloch waves). They are applied to the interpretation of the main properties of dynamical diffraction: anomalous transmission, standing waves and Pendellosung. The expressions for the diffracted intensity are given in both the transmission (Section 5.1.6) and the reflection (Section 5.1.7) cases. The last part (Section 5.1.8) concerns the diffraction of real and spherical waves, which is described in a qualitative way.

Computational Atmospheric Acoustics

Abstract: Preface. 1. Introduction. 2. Unbounded homogeneous atmosphere. 3. Homogeneous atmosphere above a ground surface. 4. Atmospheric refraction. 5. Atmospheric turbulence. 6. Irregular terrain. 7. Noise barriers. A. Basic acoustic equations for a homogeneous atmosphere. B. Free field of a point source. C. Acoustic impedance. D. Reflection of sound waves. E. Basic acoustic equations for a layered refracting atmosphere. F. Generalized Fast Field Program (FFP). G. Parabolic Equation (PE) method. H. Green's Function Parabolic Equation (GFPE) method. I. Atmospheric turbulence. J. Atmospheric turbulence in the PE method. K. Analytical model for a non-refracting turbulent atmosphere. L. Ray model including caustic diffraction fields. M. Computational methods for irregular terrain. N. Wind and temperature profiles in the atmosphere. O. Sound propagation over a screen. P. The method of stationary phase. References. List of symbols. Index.

Periodic light coupler gratings in amorphous thin film solar cells

Abstract: Efficient light trapping structures for amorphous hydrogenated silicon (a-Si:H) solar cells have been realized using periodically structured aluminum doped zinc oxide (ZnO:Al) with periods between 390 and 980 nm as a transparent front contact. Atomic force microscopy, optical reflection, and diffraction efficiency measurements were applied to characterize solar cells deposited on such gratings. A simple formula for the threshold wavelength of total internal reflection is derived. Periodic light coupler gratings reduce the reflectance to a value below 10% in the wavelength range of 400–800 nm which is comparable to cells with an optimized statistical texture. Diffraction efficiency measurements and theoretical considerations indicate that a combination of transmission and reflection gratings contribute to the observed reduction of the reflectance.

Transverse waves in numerical simulations of cellular detonations

Abstract: In this paper the structure of strong transverse waves in two-dimensional numerical simulations of cellular detonations is investigated. Resolution studies are performed and it is shown that much higher resolutions than those generally used are required to ensure that the flow and burning structures are well resolved. Resolutions of less than about 20 numerical points in the characteristic reaction length of the underlying steady detonation give very poor predictions of the shock configurations and burning, with the solution quickly worsening as the resolution drops. It is very difficult and dangerous to attempt to identify the physical structure, evolution and effect on the burning of the transverse waves using such under-resolved calculations. The process of transverse wave and triple point collision and reflection is then examined in a very high-resolution simulation. During the reflection, the slip line and interior triple point associated with the double Mach configuration of strong transverse waves become detached from the front and recede from it, producing a pocket of unburnt gas. The interaction of a forward facing jet of exploding gas with the emerging Mach stem produces a new double Mach configuration. The formation of this new Mach configuration is very similar to that of double Mach reflection of an inert shock wave reflecting from a wedge.

Primary radiator for parabolic antenna and converter for satellite broadcast reception

Abstract: PROBLEM TO BE SOLVED: To suppress multiple reflection inside a horn, and to obtain excellent reflection loss characteristics and superior circular polarization axis ratio characteristics over a wide frequency range. SOLUTION: A horn section 12 for receiving radio waves from a parabolic reflector is provided at the front opening of a case body 11, and at the same time a horn cover 21 is provided at the opening of the horn section 12. Inside the case body 11, a circular polarization generator 13 and a feeding section 14 are provided. In the circular polarization generator 13, a rod-shaped support section 22 is provided at the side of the horn section 12, a cylindrical dielectric 23 is provided at the tip in one piece. The cylindrical dielectric 23 is set to a length of approximately 1/4 wavelength of an incident radio wave multiplied by the wavelength reduction rate of the dielectric, and is positioned near the center of the opening at the horn section 12. The cylindrical dielectric 23 is provided independently of the horn cover 21, thus forming the horn cover 21 sufficiently thinly, suppressing the multiple reflection inside the horn without reducing the reception level of the antenna, and hence obtaining excellent electric characteristics.

Neutron reflectivity at the solid/liquid interface : examples of applications in biophysics

Abstract: Over the last 20 years, neutron reflection has emerged as a powerful technique for investigating inhomogeneities across an interface, inhomogeneities either in composition (Lu and Thomas 1998 J. Chem. Soc. Faraday Trans. 94 995) or magnetization (Felcher 1981 Phys. Rev. B 24 1995). By measuring the reflected over the incoming intensity of a well collimated beam striking at an interface, as a function of the incident angle and wavelength, the concentration profile giving rise to a reflectivity curve is calculated. The success of neutron reflection arises from the fact that, because of the short wavelengths available, it has a resolution of a fraction of a nanometre, so that information is gained at the molecular level. Unlike x-rays it is not destructive and can be used at buried interfaces, which are not easily accessible to other techniques, such as liquid/liquid or solid/liquid, as well as at solid/air and liquid/air interfaces. It is particularly useful for soft-matter studies since neutrons are strongly scattered by light atoms like H, C, O and N of which most organic and biological materials are formed. Moreover, the nuclei of different isotopes of the same element scatter neutrons with different amplitude and sometimes, as in the case of protons and deuterons, with opposite phase. This allows the use of the method of contrast variation, described below, and different parts of the interface may be highlighted. For biophysics studies, a major advantage of reflectivity over other scattering techniques is that the required sample quantity is very small (<10-6 g) and it is therefore suitable for work with expensive or rare macromolecules. While specular reflection (angle of incoming beam equal to angle of reflected beam) gives information in the direction perpendicular to the interface, the lateral structure of the interface may be probed by the nonspecular scattering measured at reflection angles different from the specular one (Sinha et al 1998 Phys. Rev. B 38 2297, Pynn 1992 Phys. Rev. B 45 602). This technique is widely used with x-rays while there are far fewer data in the neutron case due to the smaller intensity of neutron beams. An example relevant in biophysics where the neutron technique has been applied is the off-specular scattering from highly oriented multilamellar phospholipid membranes (Munster et al 1999 Europhys. Lett. 46 486). Neutron reflection is now being used for studies of surface chemistry (surfactants, polymers, lipids, proteins and mixtures adsorbed at liquid/fluid and solid/fluid interfaces), surface magnetism (ultrathin Fe films, magnetic multilayers, superconductors) and solid films (Langmuir-Blodgett films, thin solid films, multilayers, polymer films). The number of reflectometers in the neutron facilities all around the world is increasing although the use of the technique is not yet very common because the availability of beam time is restricted by cost. Since many biological processes occur at interfaces, the possibility of using neutron reflection to study structural and kinetic aspects of model as well as real biological systems is of considerable interest. However, the number of such experiments so far performed is small. The reason for this is probably because it is well known that the most effective use of neutron reflection involves extensive deuterium substitution and this is not usually an available option in biological systems. This problem may be partially solved by deuteriating other parts of the interface as described by Fragneto et al (2000 Phys. Chem. Chem. Phys. 2 5214). In this paper we shall concentrate on the use of specular neutron reflection at the solid/liquid interface, less studied than the solid/air or liquid/air interfaces, although technologically more important. After a brief introduction to the theory and measurement of neutron reflectivity, solid/liquid interfaces both from hydrophilic and hydrophobic solids will be described. Three examples of applications in biophysics will be given: (1) the adsorption of two proteins, β-casein and β-lactoglobulin, on hydrophobic silicon; (2) the interaction of the peptide p-Antp43-58 with phospholipid bilayers deposited on silicon; (3) the fluid floating bilayer, a new model for biological membranes.

The Use of Ultrasound in the Investigation of Rough Surface Interfaces

Abstract: The measurement of ultrasonic reflection has been used to study the contact between rough surfaces. An incomplete interface will reflect some proportion of an incident wave; this proportion is known as the reflection coefficient, If the wavelength is large compared with the width of the gaps in the plane of the interface then the reflection mechanism can be modeled by considering the interface as a spring. The proportion of the incident wave reflected (reflection coefficient) is then a function of the stiffness of the interface and the frequency of the ultrasonic wave. The sensitivity of the ultrasonic technique has been quantified using a simple model, from which the stiffness of individual gaps and contacts are calculated and their effect on the ultrasonically measured stiffness predicted. The reflection of ultrasound at a static interface between a rough, nominally flat aluminum plate and a rough, nominally flat hardened steel punch has been investigated. Plastic flow on first loading was evident, while repeated loading was largely elastic. However, subsequent cycles indicate a small amount of further plasticity and contact irreversibility. The effect of surface roughness on the resultant contact has also been investigated. A simple plastic contact model is described which allows prediction of the average size of the asperity contacts and their number. This model shows that the average size of the contacts remains constant over most of the loading whereas the number of contacts increases almost linearly. The contact stiffness has also been modeled with two well known elastic rough surface contact models. These models predicted a lower interface stiffness than was observed in the experiments. However they provide a useful way of interpreting the ultrasonically measured interface stiffness data.

Phase-dispersion optical tomography

Abstract: We report on phase-dispersion optical tomography, a new imaging technique based on phase measurements using low-coherence interferometry. The technique simultaneously probes the target with fundamental and second-harmonic light and interferometrically measures the relative phase shift of the backscattered light fields. This phase change can arise either from reflection at an interface within a sample or from bulk refraction. We show that this highly sensitive 5 phase technique can complement optical coherence tomography, which measures electric field amplitude, by revealing otherwise undetectable dispersive variations in the sample.

Laser survey instrument

Abstract: A laser survey instrument, which comprises at least a main unit for emitting a laser beam and an object reflector for reflecting the laser beam from the main unit toward the main unit, whereby said main unit comprises an emitter for emitting the laser beam, a rotating unit for rotating and scanning the laser beam, a tilting mechanism for tilting the laser beam at an arbitrary angle at least in one direction with respect to a horizontal plane, a rotating angle detector interlocked with the rotating unit and for detecting irradiating direction of the laser beam, a reflection light detector for detecting reflection light from the object reflector, and an alignment display unit for detecting a deviation of direction with respect to the object reflector and a deviation of tilt angle based on a signal from the reflection light detector and for obtaining information on the deviation of direction or the tilt angle, the laser beam emitted from the main unit is irradiated to scan, the center of the object reflector is determined based on the laser beam reflected from the object reflector during scanning process, information on a deviation of direction of the main unit and a deviation of tilt angle is displayed, or direction and tilt angle of the main unit are corrected automatically based on the deviation of direction thus obtained or on the deviation of tilt angle thus obtained.

Determining reflectance parameters and illumination distribution from a sparse set of images for view-dependent image synthesis

Abstract: A framework for photo-realistic view-dependent image synthesis of a shiny object from a sparse set of images and a geometric model is proposed. Each image is aligned with the 3D model and decomposed into two images with regards to the reflectance components based on the intensity variation of object surface points. The view-independent surface reflection (diffuse reflection) is stored as one texture map. The view-dependent reflection (specular reflection) images are used to recover the initial approximation of the illumination distribution, and then a two step numerical minimization algorithm utilizing a simplified Torrance-Sparrow reflection model is used to estimate the reflectance parameters and refine the illumination distribution. This provides a very compact representation of the data necessary to render synthetic images from arbitrary view points. We have conducted experiments with real objects to synthesize photorealistic view-dependent images within the proposed framework.

Separation of diffuse and specular reflection in color images

Abstract: The presence of specular reflections in images can lead many traditional computer vision algorithms to produce erroneous results. To address this problem, we propose a method based on the neutral interface reflection model for separating the diffuse and specular reflection components in color images. From two photometric images without calibrated lighting, the illuminant chromaticity is estimated, and the RGB intensities of the two reflection components are computed for each pixel using a linear model of surface reflectance. Unlike most previous methods, the presented technique does not assume any dependencies among pixels, such as regionally uniform surface reflectance.

Vehicle surroundings monitoring device

Abstract: A vehicle surroundings monitoring device in which reflection by a mirror is reduced to ensure the desired performance of distance measurement even in a short-distance range. The monitoring device for monitoring surroundings around a vehicle has a transmitting antenna provided in a door mirror assembly of the vehicle to radiate transmitted waves through a mirror surface of the door mirror, and a receiving antenna provided in the door mirror assembly to receive, through the door mirror surface, reflected waves from an object existing near the vehicle. In the this monitoring device, electric wave transmission surfaces are formed as portions of the door mirror surface corresponding to openings surfaces for the transmitting and receiving antennas to limit reflection by the door mirror surface and to enable transmission of electric waves through the door mirror surface. The electric wave transmission surfaces are formed by partially removing a reflective film formed on the mirror surface, by partially cutting off the mirror surface, or by forming metal slits in portions of the door mirror surface or through the entire door mirror surface.

A staggered-grid finite-difference method with perfectly matched layers for poroelastic wave equations

Abstract: A particle velocity-strain, finite-difference (FD) method with a perfectly matched layer (PML) absorbing boundary condition is developed for the simulation of elastic wave propagation in multidimensional heterogeneous poroelastic media. Instead of the widely used second-order differential equations, a first-order hyperbolic leap-frog system is obtained from Biot’s equations. To achieve a high accuracy, the first-order hyperbolic system is discretized on a staggered grid both in time and space. The perfectly matched layer is used at the computational edge to absorb the outgoing waves. The performance of the PML is investigated by calculating the reflection from the boundary. The numerical method is validated by analytical solutions. This FD algorithm is used to study the interaction of elastic waves with a buried land mine. Three cases are simulated for a mine-like object buried in “sand,” in purely dry “sand” and in “mud.” The results show that the wave responses are significantly different in these cases. The target can be detected by using acoustic measurements after processing.

Structure and the Reflectionless/Refractionless Nature of Parabolic Diffusion-Wave Fields

Abstract: We show the impossibility of reflection and refraction phenomena at linear diffusion-wave-field (DWF) interfaces. Instead, interfacial flux expressions are derived which involve coherent accumulation or depletion phenomena subject to an interface flux conservation principle. The conditions for reflectionless and refractionless interfaces are the parabolic nature and the concomitant Fickian constitutive relations satisfied by DWFs. Simulations show that the reflection and Snell's laws can be adequate approximations only under near-normal incidence conditions, in agreement with published experimental evidence in wide areas of biomedical, electronic, and materials physics.

Reflection and refraction optical system and projection exposure apparatus using the same

Abstract: A reflection and refraction optical system includes a polarization beam splitter, a concave mirror, a lens group and a quarter waveplate, wherein an additional waveplate is provided to transform S-polarized light from the polarization beam splitter into circularly polarized light.

Broadband Time-Domain Impedance Models

Abstract: The modeling of a set of impedance values given either experimentally or heuristically for implementation as a time-domain impedance-equivalent boundary condition (TDIBC) is discussed. It is shown that impedance as defined by the reflection of plane harmonic waves when extended for broadband time-domain applications can correspond to mathematically feasible but physically unacceptable noncausal reflection processes. Given a set of impedance data on a finite, positive, and real frequency range, it is possible to construct causal time-domain models that render efficient implementation of TDIBC for broadband reflections. However, these models defined by measurement of harmonic waves may not be valid for the reflection of impulses, for which measurement of transient reflections is warranted.

Field Measurements of Sediment Dynamics in Front of a Seawall

Abstract: A field experiment has been carried out to examine the effects of seawalls on hydrodynamic and sediment dynamic processes on sandy beaches Pressure transducers, electromagnetic current meters and optical backscatter sensors were deployed directly in front of a seawall at Teignmouth, South Devon (UK) in June 1995 Similar instruments were deployed simultaneously on the adjacent natural beach Reflection coefficients were in the range 07 to 10 at the wall and around 02 on the natural beach for incident wave frequencies (0125-036 Hz) Reflection coefficients at lower frequencies (004-0125 Hz), were close to unity at the wall, whilst on the beach the reflection coefficient increased with decreasing frequency, reaching 09 at the low frequency spectral peak Both sediment suspension and transport were altered significantly by the presence of the wall Mean suspended sediment concentrations were found to be up to three times larger in front of the wall than on the natural beach This increase was attributed to the increase in wave reflection The largest differences occurred when the waves were largest, and the water was shallow A net onshore sediment transport by incident waves was observed on the natural beach In front of the wall, this net oscillatory transport was considerably reduced The longshore current in front of the wall was stronger than that observed on the natural beach Combined with the increase in suspended sediment, this enhanced longshore current resulted in a longshore sediment transport rate which was an order of magnitude greater in front of the wall than on the natural beach

The effects of a Comptonizing corona on the appearance of the reflection components in accreting black hole spectra

Abstract: We discuss the effects of a Comptonizing corona on the appearance of the reflection components, and in particular of the reflection hump, in the X-ray spectra of accreting black holes. Indeed, in the framework of a thermal corona model, we expect that some (or even all, depending on the coronal covering factor) of the reflection features should cross the hot plasma, and thus suffer Compton scattering, before being observed. We have studied in detail the dependence of these effects on the physical (i.e. temperature and optical depth) and geometrical (i.e. inclination angle) parameters of the corona, concentrating on the slab geometry. Owing to the smoothing and shifting towards high energies of the Comptonized reflection hump, the main effects on the emerging spectra appear above 100 keV. We have also investigated the importance of such effects on the interpretation of the results obtained with the standard fitting procedures. We found that fitting Comptonization models, taking into account Comptonized reflection, by the usual cut-off power law + unComptonized reflection model may lead to an underestimation of the reflection normalization and an overestimation of the high-energy cut-off. We discuss and illustrate the importance of these effects by analysing recent observational results, such as those of the galaxy NGC 4258. We also find that the Comptonizing corona can produce and/or emphasize correlations between the reflection feature characteristics (like the iron line equivalent width or the covering fraction) and the X-ray spectral index, similar to those recently reported in the literature. We also underline the importance of these effects when dealing with accurate spectral fitting of the X-ray background.

Note on an exact solution for magnetoatmospheric waves

Abstract: Solutions for magnetoatmospheric waves in an isothermal plane stratified atmosphere with uniform vertical magnetic field have long been known in terms of Meijer G-functions. It is pointed out that they may alternatively be expressed using the more familiar hypergeometric 2F3 functions, with significant advantages for ease of use and physical interpretation. The nature of these solutions in different regions of the frequency-wavenumber plane is fully discussed, with particular reference to reflection, transmission, and mode conversion. Reflection, transmission, and mode conversion coefficients for slow and fast waves incident from below, including the effects of tunnelling, are calculated exactly. The exact solutions are useful in interpreting observational results and numerical simulations of more complex magnetoatmospheric waves.

BOUSS-2D: A Boussinesq Wave Model for Coastal Regions and Harbors

Abstract: : BOUSS-2D is a comprehensive numerical model for simulating the propagation and transformation of ocean waves in coastal regions and harbors. The model is based on depth-integrated Boussinesq-type mass and momentum equations for nonlinear-dispersive waves. The equations describe most of the wave transformation phenomena of interest in coastal regions and harbors including shoaling, refraction, diffraction, reflection, nonlinear wave-wave interactions, and wave breaking. This manual describes the theoretical background behind the model and the steps involved in setting up and running the model.

Probing interface electronic structure with overlayer quantum-well resonances: Al/Si(111).

Abstract: The dispersion of quantum-well resonances in ultrathin epitaxial Al films on Si(111) reveals energy- and wave vector-dependent reflection properties at the Al/Si interface. The substrate electronic structure strongly influences the phase shift of the electron waves upon reflection at the interface. Thus the details of the substrate electronic structure need to be taken into account for a complete analysis of metallic quantum-well resonances. Furthermore, the assumption of loss of parallel wave vector information upon reflection or transmission through a lattice-mismatched interface is challenged. The changes induced in the electronic structure of the overlayer can be used to probe the ground-state substrate band edges.