Showing papers on "Total external reflection published in 2006"

Experimental demonstration of negative index of refraction

Abstract: We introduce an improved and simplified structure made of periodic arrays of pairs of H-shaped metallic wires that offer a potentially simpler approach in building negative-index materials. Using simulations and microwave experiments, we have investigated the negative-index n properties of these structures. We have measured experimentally both the transmittance and the reflectance properties and found unambiguously that a negative refractive index with Re(n)<0 and Im(n)

Slow propagation, anomalous absorption, and total external reflection of surface plasmon polaritons in nanolayer systems.

Abstract: I predict that a nanoscopic, high-permittivity layer on the surface of a plasmonic metal can cause total external reflection of surface plasmon polaritons (SPPs). Such a layer can be used as a mirror in nanoplasmonics, in particular for resonators of nanolasers and spasers and can also be used in adiabatic nanooptics. I also show that the earlier predicted slow propagating SPP modes, especially those with negative refraction, are highly damped.

Effect of changes in size and index of refraction on the resonance wavelength of microspheres

Abstract: Wave theory and geometrical optics are used to investigate the effect of small changes in size and index of refraction on the resonance wavelength of spherical microresonators. It is shown that changes in the index of refraction have two effects: These changes affect the phase jump on the surface and the optical path length in the resonator. Under certain conditions the effect of the external or internal index of refraction becomes negligible. The influence of the order number of the resonance modes is investigated. Finally, the results of the theoretical analyses are applied to calculate the effect of temperature on the resonance wavelength.

Electrodynamics of moving media inducing positive and negative refraction

Abstract: Negative refraction is a phenomenon that has been recently reported with left-handed media (either isotropic or not), photonic crystals, and rotated uniaxial media. In this Brief Report, we identify another origin of negative refraction, due to the motion of the transmitted medium parallel to the interface at which refraction occurs. Previous works in this domain have concentrated on media velocities that are above the Cerenkov limit, while we show here that negative refraction is in fact achievable at any velocities of the transmitted medium. A possible experimental implementation is proposed to verify this effect. Next, we consider an isotropic frequency-dispersive medium for which the index of refraction can take negative values, and we study the wave refraction phenomenon as a function of frequency and medium velocity. It is found that the motion of the medium induces a rotation of refraction, which can either enhance or attenuate the natural negative refraction of the medium.

On the dynamical effects in the characteristics of transition radiation produced by a relativistic electron in a single crystal plate

Abstract: This article reports on the transition radiation (TR) of a relativistic electron crossing a crystalline plate, which in the Bragg’s scattering geometry is considered within the framework of the X-ray diffraction dynamical theory. The expressions for TR and diffracted transition radiation (DTR) spectral–angular distribution received allow to discuss the manifestation of the dynamical approach. It is shown, that the spectral–angular characteristics of TR and DTR essentially depend on the orientation of the crystal plate surface when the angle between the electron velocity and the atomic planes is kept constant. This phenomenon is explained by the modification of the frequency range of total external reflection of the radiation under a changing target surface orientation.

Reflection and refraction of waves at the interface of an isotropic medium over a highly anisotropic medium

Abstract: In this paper, we have considered the reflection and refraction of a plane wave at an interface between two half-spaces. The lower half-spaces is composed of highly anisotropic triclinic crystalline material and the upper half-space is homogeneous and isotropic. It has been assumed that due to incidence of a plane quasi-P (qP) wave, three types of waves, namely, quasi-P (qP), quasi-SV (qSV) and quasi-SH (qSH), will be generated in the lower half space whereas P and S waves will be generated in the upper half space. The phase velocities of all the quasi waves have been calculated. It has been assumed that the direction of particle motion is neither parallel nor perpendicular to the direction of propagation. Some specific relations have been established between directions of motion and propagation, respectively. The expressions for reflection coefficients of qP, qSV, qSH and refracted coefficients of P and SV waves are obtained. Results of reflection and refraction coefficients are presented.

Control of reflection at an optical interface in the absence of total internal reflection for a retroreflective display application

Abstract: Reflection at an interface between two materials can be modulated by means of varying the optical properties at the interface. We have studied this modulation of the reflected light with an aim to develop a flashing retroreflector for roadside conspicuity applications. Reflectance modulation has previously been studied under the conditions of total internal reflection (TIR), where a light-absorbing material placed in the associated evanescent wave region can be used to attenuate the intensity of the reflected light. If instead the light rays strike the interface at an angle that is slightly smaller than the critical angle required for TIR, they instead undergo a substantial, but partial, reflection. We have demonstrated that an analogous attenuation effect to the TIR situation is observed, even though there is no evanescent wave present under these circumstances. We have studied this behavior and have developed a model to describe the motion of the absorbing material and the related interference effects that occur.

Approximate thermal emission models of a two-dimensional graded index semitransparent medium

Abstract: This study develops numerical models for thermal emission in a two-dimensional semitransparent graded-index medium. Two piecewise continuous refractive index models, the bar model and the slab model, are presented. The formal is a combination of rectangular bars each having its own unique refractive index. The latter is a combination of slabs, each of which has a linear refractive index distribution. Two interface hypotheses are discussed: the reflection/refraction hypothesis and the refraction/total reflection hypothesis. The backward ray tracing method and the backward Monte Carlo method are employed for calculation. The apparent directional emissivity of a semitransparent medium with linear and nonlinear refractive index distributions is calculated. The results show that piecewise continuous refractive index can be used for modeling semitransparent media with continuously variable refractive index. Emission from the medium is complex and quite different from a medium with a constant refractive index, when the absorption coefficient is small and/or the refractive index varies greatly in the medium. The refractive/totally reflective inner interface in the bar model gives a more precise emission distribution and can be extended to simulate emission from a medium with a complex three-dimensional refractive index distribution.

Visualization of the complex refractive index of a conductor by frustrated total internal reflection

Abstract: A simple imaging geometry in which total internal reflection in a glass prism is frustrated by the proximity of a metal surface is implemented for observation of surface plasmon resonance. At a certain angle of incidence, the total internal reflection is completely suppressed at a certain distance between the metal and the prism surfaces. Using planar metal and spherical prism surfaces, the distance parameter is sampled in a single image. This allows a direct determination of the complex refractive index in bulk samples as well as in thin films. Our experimental data are in good agreement with previously published data.

Total internal reflection for illumination and displays

Abstract: Total internal reflection (TIR) can occur when a light ray traveling in a transparent material encounters an interface with another transparent, but less optically dense material. The phenomenon is interesting not only because the reflection can be close to perfect, but because the effect depends critically on the angle of incidence. Although TIR is used widely, in this article we discuss two less well known applications with which we have considerable experience. The first example is a device known as a prism light guide, a hollow dielectric structure that can transport a large luminous flux for illuminating engineering applications. The second example is a form of electronic paper. In both cases, it is the unique characteristics of TIR that make these practical devices possible. TIR is commonly said to occur when the angle of incidence exceeds the critical angle. Yet this notion is based on the inherent approximation of the ray model of light, an idea that is physically incorrect for any system of finite extent. Rather, the finite wavefront is equivalent to a superposition of a distribution of plane waves, which in turn have a range of propagation directions. Another fundamental shortcoming is that in any real system there is some degree of absorption loss in the materials. As a result, in reality, TIR is never truly total and the critical angle is never truly critical. Nevertheless, there is a profound quantitative difference between TIR and metallic reflection. In addition, in the case of TIR, the reflection can be modified by changing the external medium, which creates interesting possibilities. It is worth considering these ideas a bit more carefully and quantitatively. Light rays traveling from plastic (n1 = 1.5) to air (n2 = 1.0) will be transmitted through the interface for small angles of incidence, and the reflectance grows rapidly as a function of angle as the angle of incidence approaches the critical angle, (see Figure 1). It is important to note how tiny the angular range is in the plot in Figure 1. For all angles of incidence below the critical anFigure 1. The graph illustrates reflectance versus angle of incidence very close to the critical angle (indicated by the dotted vertical line).

Ferromagnetic wire lattice with a tunable negative index of refraction for microwaves using an external magnetic field

Abstract: A new structure of negative-refractive-index material is proposed, which is composed of ferromagnetic wires setting in two-dimensional Bravais lattice (FWL) with the application of external magnetic field. The refractive index of the FWL consisting of ferrum wires arranged in square lattice is calculated. The refractive index exhibits negative value in the GHz region. A notable characteristic of the FWL is that the negative refractive index is tunable by the applied external field.

Pure Reflection and Refraction of a Surface Polariton by a Matched Waveguide Structure

Abstract: We study the fundamental problem of reflection and refraction of a surface polariton as it strikes the interface between two waveguide structures. By making the two waveguide structures match to each other, coupling of surface polaritons to radiating modes is cancelled, and the reflected and transmitted waves consist of only surface modes. The reflection and transmission coefficients are calculated, and negative refraction of surface polaritons is demonstrated. Finite-difference time-domain numerical simulations are also performed to verify the analytical results. As one of the applications of the matched waveguide structure, a square corner reflector for phase-retardation-free reflection of surface polaritons is proposed.

Optical filter and color separation prism

Abstract: PROBLEM TO BE SOLVED: To provide an optical filter which can be manufactured easily and has superior effects of suppressing luminance shading and color shading. SOLUTION: The optical filter 21 is made, by alternately layering a first optical film H having a first refractive index and a second optical film M1, having a second refractive index on light transmissive substrates (base plates) 11W, 12W, wherein the first refractive index is higher than the refractive index of the substrate, and the second refractive index is higher than the refractive index of the substrate and is lower than the first refractive index. By using an intermediate refractive index film, having a refractive index higher than that of the substrate and lower than that of the first optical film H as the second optical film M1, the difference in the refractive index, between first and second optical films, is reduced, and the spectroscopic characteristics shift in the optical thickness, with respect to a change in an incident angle of light, is suppressed. COPYRIGHT: (C)2008,JPO&INPIT

Light management films of differing refractive indices

Abstract: An optical layer includes a first light management film having a first index of refraction (n 1 ) and a second light management film having a second index of refraction (n 2 ). The first index of refraction and the second index of refraction are not the same, and a plurality of optical features is disposed over each of the light management films. A light management film is also disclosed.

Air core waveguides composed by elliptical metallic nanostructures operating at optical frequencies

Abstract: Air core waveguides with very low losses can be designed by removing a line of rods at the center of a periodical arrangement of elliptical metallic rods in a square lattice The use of composite nanostructures made possible the engineering of the cladding properties of the waveguides to present very low equivalent refractive index The mechanism of propagation in these kind of guides is the total external reflection In this work, the dependence of the transmission properties of these waveguides on the shape and orientation of the metallic elliptical wires are analyzed by an efficient frequency domain finite element approach

The inverse problem of estimating the film structure from X-ray reflection data

Abstract: A new model of an X-ray reflection experiment is proposed for studying the structure of a film on a substrate. The experimental data are processed to yield the density distribution across the film, and an appropriate approximation produces numerical values of the parameters { δi, βi, σi, d 1} for each of the n layers in a multilayer film model. So far there has been no method for determining the film structure from experimental data and the problem has been usually solved by trial and error.

Negative refraction in two-dimensional photonic crystals

Abstract: A two-dimensional, square-lattice photonic crystal model possessing analytical solutions is investigated to ascertain the requirements for negative refraction to occur. The refraction properties are presented for both polarizations assuming in-plane propagation and phase matching conditions across a surface perpendicular to the ΓM-direction of the crystal. It is shown that the most isotropic and highest effective refractive index is obtained near the maximum of the lowest band for a crystal with a high refractive index contrast between its constituent materials.

Effect of light with varying amplitude and frequency on a medium

Abstract: A formula for the complex refractive index of a medium exposed to light whose amplitude and frequency are varied in time is derived.

An X-ray diffraction investigation of the charge density wave transition at the NbSe2 surface

Abstract: Niobium diselenide 2H-NbSe2 is a van der Waals bonded layered structure, which undergoes a charge density wave transition (CDW). We have investigated the CDW transition in NbSe2 using grazing incidence X-ray diffraction. The evolution of a satellite reflection associated with the CDW has been observed above and below the critical angle of total external reflection in order to carry out a direct comparison between the surface and bulk behaviour. We successfully isolated the surface CDW structure on a high quality single crystal. The central finding of this thesis is that the behaviour of the surface CDW satellite differs from that in the bulk: At the surface, the CDW transition occurs at a higher temperature than in the bulk; also, the transition appears to be continuous. It is likely that we observe the unusual case defined as a “surface transition“ and not the usual case of an “ordinary transition“. A novel experimental method, grazing incidence inelastic X-ray scattering, has been demonstrated. A first successful experiment on 2H-NbSe2 where surface phonons are measured is reported.

Hybrid transmission-reflection grating

Abstract: A hybrid transmission-reflection grating includes an array of essentially parallel principal interfaces, with each principal interface separating a first medium and a second medium. The first medium has a first index of refraction, and the second medium has a second index of refraction. The first medium allows for transmission of quantum- mechanical objects in excess of one percent of an incident number of quantum-mechanical objects. The array of principal interfaces has a spacing distance between adjacent principal interfaces. The first medium has a width in the direction normal to the principal interfaces, the width being less than the spacing distance. Each principal interface has a length such that either (1) the length is greater that the width divided by tan(2tc), wherein tc is an critical angle of total external reflection for the quantum-mechanical objects at the principal interface, or (2) the length is greater that the width divided by tan(2tc), wherein tc is a critical angle defined by 2πsin(tc) σ = λ, with λ being de Broglie wavelength of the quantum-mechanical objects and σ being a roughness of the principal interface.

Air core waveguides composed by elliptical metallic nanostructures operating at optical frequencies V. F. Rodriguez-Esquerre, C. E. Rubio-Mercedes, and H. E. Hernández-Figueroa

Abstract: Air core waveguides with very low losses can be designed by removing a line of rods at the center of a periodical arrangement of elliptical metallic rods in a square lattice. The use of composite nanostructures made possible the engineering of the cladding properties of the waveguides to present very low equivalent refractive index. The mechanism of propagation in these kind of guides is the total external reflection. In this work, the dependence of the transmission properties of these waveguides on the shape and orientation of the metallic elliptical wires are analyzed by an efficient frequency domain finite element approach. Index Terms — Metamaterials, finite element methods, metals, photonic crystals, elliptical nanowires.

Reflection model for optical switch with total-internal-reflection structure

Abstract: We propose an analytical reflection model for the waveguide switch with total-internal-reflection structure, which is the grazing reflection of beam with narrow beamwaist For such incidence condition, the output optical field is the superposition of incident and reflected fields, we deduce the effective reflection coefficient together with angular spectrum of the output field

Method and device for reflection of radiation in the euv or x-ray wavelength range and method for producing a material having a refractive index sutiable therefor

Abstract: A description is given of a method for reflection of radiation (5) in the EUV or X-ray wavelength range with the application of at least one reflective interface (3) a first material (2) having a first refractive index (n1) being provided on a side of the interface (3) that is intended for the incidence of the radiation (5) , and a second material (1) having a second refractive index (n2) being provided on that side of the interface (3) which is remote from the incident radiation (5), and a preselected angle (ai) of incidence being used for the incident radiation (5). According to the invention, in the case the wavelength range of the radiation (5) used, the first refractive index (n1) is greater than the second refractive index (n2). Moreover, for the radiation (5) an angle (ai) of incidence is chosen which is greater than 0 and is less than the angle (ac) of total reflection at most by an amount such that the total reflectivity at the interface (3) for the wavelength range chosen is greater than at an angle of incidence aI = 0°. In addition, a description is given of a method for producing a material which is particularly well suited to the method according to the invention, and a device suitable for EUV lithography and for the masking technique (Figure 1).

Multipurpose spectrometer TERLAB for depth selective investigation of surface and multilayer

Abstract: The multipurpose spectrometer for nondestructive, depth selective investigation of physical and chemical properties of a surface and bulk is described. It realizes opportunities of Mossbauer and X-ray Fluorescence Spectroscopy in normal and TER-conditions, Mossbauer and X-ray diffractometry and also Mossbauer and X-ray Reflectometry. Some analytical characteristics and capabilities of a spectrometer are illustrated as an example of research with a model sample.

Optical response and light scattering measurements from a planar guided wave

Abstract: Experimental results of reflection and light scattering measurements using the technique of attenuated total reflection (ATR) in the Kretschmann configuration of a system when it is excited an electromagnetic guided mode are reported. The system used is BK7 glass-prism/Dielectricl/Dielectric2/Dielectricl/air, where the refractive index of dielectric 1 is less than the refractive index of the dielectric2. It was found a dip in the specular reflection as a function of the incident angle due to the excitation of a guided mode in the dielectric2 film. The guided mode was found for s polarization of the incident light. The angular dependence of the scattered light displays a peak caused by single-scattering and located approximately at the angles of excitation of the guided modes whose normalized wave numbers are less than the refractive index of the glass. Values of thickness, refractive index and absorption index obtained from Lorentz dispersion model of the film are reported.

Arrangement of Equivalent Thin Metal Film to Have Narrow Attenuated Total Reflection Curve

Abstract: In this study, we analyze the attenuated total reflection spectra by interpreting two virtual modes in a Kretschmann configuration. Provided that the reflectance minimum remains zero, the damping of the surface plasmon can be modulated to yield a narrower attenuated total reflection (ATR) spectrum. A multilayered structure is designed between a prism and a metal film. An equivalent metal film with a high index of extinction to index of refraction ratio yields ATR angular and wavelength spectra that are narrower than the spectra obtained from a single metal film.

Interferometric Control of the Absorbing Liquids

Abstract: The attenuated total internal reflection (ATIR) is an area of constant interest. The reason for that is the great variety of useful applications based on this phenomenon. In this paper we describe a simple interferometric phasemeter which can be used to control the presence of absorption in water solutions. In the process of the attenuation of the total internal reflection in a three layer system the phase shift between both main polarization components of the reflected field is strongly dependent on the complex value of the index of refraction of the second media. This method is based on the interferometric restoration of both p- and s-components of the resultant field. The resulting interferometrical signal is modeled theoretically and studied experimentally.