Showing papers on "Total external reflection published in 2003"

Electromagnetic waves: Negative refraction by photonic crystals.

Abstract: Materials that can bend light in the opposite direction to normal ('left-handed' materials) reverse the way in which refraction usually works — this negative refractive index is due to simultaneously negative permeability and permittivity1,2,3. Here we demonstrate negative refraction of electromagnetic waves in a two-dimensional dielectric photonic crystal that has a periodically modulated positive permittivity and a permeability of unity4,5,6. This experimental verification of negative refraction is a step towards the realization of a 'superlens' that will be able to focus features smaller than the wavelength of light.

Refraction in media with a negative refractive index.

Abstract: We show that an electromagnetic (EM) wave undergoes negative refraction at the interface between a positive and negative refractive index material, the latter being a properly chosen photonic crystal. Finite-difference time-domain (FDTD) simulations are used to study the time evolution of an EM wave as it hits the interface. The wave is trapped temporarily at the interface, reorganizes, and, after a long time, the wave front moves eventually in the negative direction. This particular example shows how causality and speed of light are not violated in spite of the negative refraction always present in a negative index material.

Gradient immersion lithography

Abstract: In a lithographic projection apparatus, a space between an optical element of a projection system is filled with a first fluid and a second fluid separated by a translucent plate. The first and second fluids have first and second indices of refraction, respectively, that are different from one another. The first fluid is provided in a space between a substrate and the translucent plate and preferably has an index of refraction similar to the index of refraction of the substrate. The second fluid is provided in a space between the translucent plate and the optical element and preferably has an index of refraction similar to the index of refraction of the optical element. The translucent plate has a third index of refraction between the first and second indices of refraction. The third index of refraction may be equal to the first index of refraction or the second index of refraction. A device manufacturing method includes filling a space between the optical element and the substrate with at least two fluids having different indices of refraction.

Total negative refraction in real crystals for ballistic electrons and light.

Abstract: It is found that there exists a category of material interfaces, readily available, that not only can provide total refraction (i.e., zero reflection) but can also give rise to amphoteric refraction (i.e., both positive and negative refraction) for electromagnetic waves in any frequency domain as well as for ballistic electron waves. These two unusual phenomena are demonstrated experimentally for the propagation of light through such an interface.

Total external reflection from metamaterials with ultralow refractive index

Abstract: Metamaterials composed of metal-dielectric nanostructures are engineered to have an effective refractive index less than unity at optical wavelengths. The effect of total external reflection is demonstrated when light from vacuum is incident onto these materials at an angle exceeding the critical angle defined by Snell’s law. Novel approaches are discussed to derive the effective index of refraction from the reflection and refraction properties of finite slabs. The effect of losses and dispersion are analyzed in the visible range of frequencies by consideration of the measured properties of silver. The differences among ultralow refractive-index metamaterials, photonic bandgap materials, and metals are discussed. Remarkably, a bandgap is not required to obtain total external reflection.

Time-resolved pulse propagation in a strongly scattering material.

Abstract: Light transport in macroporous gallium phosphide, perhaps the strongest nonabsorbing scatterer of visible light, is studied using phase-sensitive femtosecond pulse interferometry. Phase statistics are measured at optical wavelengths in both reflection and transmission and compared with theory. The diffusion constant of light is measured in both reflection and transmission as a function of thickness and compared with theories for diffusive transport and localization. An unusually high energy velocity due to the bicontinuous structure of the porous network is reported. For such strongly scattering samples, we show that surface properties and the effective index of refraction need to be treated carefully.

Amplified total internal reflection.

Abstract: Totally internal reflected beams can be amplified if the lowerindex medium has gain. We analyze the reflection and refraction of light, and analytically derive the expression for the Goos-Hanchen shifts of a Gaussian beam incident on a lower-index medium, both active and absorptive. We examine the energy flow and the Goos-Hanchen shifts for various cases. The analytical results are consistent with the numerical results. For the TE mode, the Goos-Hanchen shift for the transmitted beam is exactly half of that of the reflected beam, resulting in a "1/2" rule.

Anisotropy and oblique total transmission at a planar negative-index interface

Abstract: We show that a class of negative index (n) materials has interesting anisotropic optical properties, manifest in the effective refraction index that can be positive, negative, or purely imaginary under different incidence conditions. With dispersion taken into account, reflection at a planar negative-index interface exhibits frequency selective total oblique transmission that is distinct from the Brewster effect. Finite-difference-timedomain simulation of realistic negative-n structures confirms the analytic results based on effective indices.

Dynamics of causal beam refraction in negative refractive index materials

Abstract: A finite difference simulation of a causally excited electromagnetic Gaussian beam incident on an interface between free space and a physically realizable negative refractive index material shows that negative refraction of finite beams does occur. A discontinuity in the phase normal direction is established very quickly when the beam front reaches the interface of positive and negative index materials. Once the beam enters the negative index material, the causal wave-front propates with the group velocity consistent with theory. During the transient portion of the beam development, the beam undergoes small direction changes, which can be explained as a consequence of higher frequencies present during the beam turn-on. After this transient, the theoretically predicted sinusoidal steady state is reached.

Varying refractive index optical medium using at least two materials with thicknesses less than a wavelength

Abstract: An optical medium has a graded effective refractive index with a high maximum refractive index change. The medium is formed using alternating layers of two or more materials having significantly different refractive indices. The thickness of the layers of at least one of the materials is substantially less than the effective light wavelength of interest. The effective index of refraction in a local region within the medium depends on the ratio of the average volumes of the two materials in the local region. A graded index of refraction is provided by varying the relative thicknesses of the two materials.

Total reflection X-ray fluorescence study of Langmuir monolayers on water surface

Abstract: X-ray total external reflection fluorescence has been applied to detect an angular dependence of fluorescence yield modulated by evanescent/X-ray standing wave pattern from metal-rich organic monolayer alone on water surface. Theoretical consideration reveals that electric field intensity in a molecular monolayer is completely determined by an area per one molecule value that can be obtained from pressure-area isotherm. This allows getting an ion position inside a monolayer from the corresponding fluorescence angular dependence. The possibilities of the technique have been used at the SR beamline ID10B (ESRF) to characterize Langmuir monolayers of phthalocyanines and cyclolinear polyorganosiloxanes formed on air/water interface.

Transmission measurements in wedge-shaped absorbing samples: an experiment for observing negative refraction.

Abstract: We report on experiments of light transmissivity, at wavelengths of 532 nm and 400 nm, through an Au film with a wedge shape. Our results exhibit a resemblance with those reported for observing negative refraction in proposed left-handed materials. This resemblance is present even though the medium that we used is well known to be right handed with its refractive index, therefore, having a positive real part. Analogous results are obtained with a glass wedge at 320 nm where absorption dominates. The experiment is explained by the wave losses that dominate over propagation, as in the already reported observation of negative refraction in developed metamaterial wedges. We design and propose an experiment with metamaterials by using thicker wires and parallel face slabs, in correspondence with light measurements that we have carried out in positive refractive index samples. This experimental configuration should conclusively determine whether refraction is positive or negative.

The reality of negative refraction

Abstract: One of the most fundamental phenomena in optics is refraction. When a beam of light crosses the interface between two different materials, its path is altered depending on the difference in the refractive indices of the materials. The greater the difference, the greater the refraction of the beam. For all known naturally occurring materials the refractive index assumes only positive values. But does this have to be the case?

Material with spectrally selective reflection

Abstract: A material with spectrally selective reflection in the primary valences of red, green and blue is applied preferably onto laser projection screens in order to make possible the projection even in daylight. In a first embodiment, a first layer of a material that is highly reflective over the entire range of visible light, e.g., aluminum is applied onto a substrate, e.g., glass or a synthetic material, followed by a second layer of a material that is essentially non-absorbing over the entire range of visible light, e.g., SiO 2 . A third layer in contact with air is applied to the second layer and is made of a material that is partially transmissive over the entire range of visible light, e.g., of NiCr An alternative embodiment comprise five layers, The first layer is made a material with a high index of refraction, e.g.; TiO 2 , a second of a material with a low index of refraction, e.g., SiO 2 , the third of a material with a high index of refraction, e.g., TiO 2 : a fourth of a material with a low index of refraction. e.g., SiO 2 , and a fifth layer of a material with a high index of refraction, e.g., TiO 2 .

Transformation of intensity fluctuations in nonlinear reflection of light

Abstract: The transformation of intensity fluctuations accompanying the nonlinear resonance reflection of light from a glass-resonant gas interface is discussed. The illumination of the interface at angles close to the critical angle for total internal reflection is found to have certain advantages over orthogonal incidence. At the maximum of the strongest resonance, the reflected light intensity amounts to more than 50% of the incident light. In these conditions, a squeezing of the amplitude (photon) fluctuations is observed in the radiation generated by a semiconductor laser-nonlinear selective reflector system. A simple semiclassical theory adequately describes some important characteristics of this system: the shape of the reflection resonances, the strength of the saturation fields, and so on.

Internal refractive index changes affect light transport in tissue

Abstract: This investigation explores the effect of index of refraction, as an optical property, on light transport through optically turbid media. We describe a model of light propagation that incorporates the influence of refractive index mismatch at boundaries within a domain. We measure light transmission through turbid cylindrical phantoms with different distributions of refractive index. These distributions approximate the heterogeneous, layered nature of biological tissue. Finite element method model calculations of diffuse transmittance through these phantoms show good agreement with the trends observed experimentally. We see that phase measurements of light that propagates through approximately 90 (mm) of scatter-dominated media may vary by 10 degrees depending upon the values of refractive index of the medium. Amplitude measurements are not as sensitive to this parameter as phase. Model calculations of diffuse reflectance from a semi-infinite slab geometry with different layers also shows good agreement with Monte Carlo simulations. We conclude that incorporating refractive index into light transport models may be worthwhile. Applying such a model in tomographic image reconstruction may improve the estimation of optical properties of biological tissues.

Vehicle light unit splits illumination from source into beams undergoing repeated total internal reflection, refraction or single total internal reflection, before leaving

Abstract: The first and second long sides (5, 11) are shaped to split light passing through the entry surface (13) into two or more light beams (16, 21, 23, 26). The first beam (16) undergoes successive total internal reflection at two surfaces (17, 19). It leaves the optical conductor (2, 34) at the exit surface (5). A second beam (21), only undergoes refraction at the first long side (5). Additionally or alternatively, a third light beam (23) undergoes total internal reflection at a side of the optical conductor facing the source, to leave via the exit surface (5).

Retro-reflection of round fibers

Abstract: Optical properties of round fibers are studied analytically and experimentally. By means of geometric optics and luminosity, the surface reflection, internal surface reflection, and transmission light of fibers are analyzed with a nearly ideal fiber, a glass rod. The angle and intensity of light scattered from a round glass rod is measured. The distribution scope of the surface reflection is 360°, and the distribution of the intensity takes the shape of an M. The scope of transmission is greater than 180°, the distribution shape of the intensity is a bell, and the maximum intensity is in the same direction as the incidence light. The distribution of internal surface reflection is narrow, the distribution of the intensity has a U shape, and the intensity reaches the maximum at the borderline. The scope of internal surface reflection decreases with the increasing refractive index of the fibers. When the index is 2, the direction of the internal surface reflection points to the light source, and it is not related to the incident angle of light.

X-ray specular reflection under conditions of extremely asymmetric noncoplanar diffraction from a bicrystal

Abstract: The angular dependence of the intensities of X-ray specular reflection has been rigorously analyzed under conditions of noncoplanar grazing Bragg diffraction in a crystal coated with a crystalline film (bicrystal). It is shown that the anomalous angular dependence of the specular-reflection intensity is extremely sensitive to the thickness (from fractions of a nanometer up to several nanometers), deformation, and the amorphization degree of the crystalline films. The optimum conditions for recording intensities are attained at grazing angles equal to 1.5–4.0 of the critical angle of the total external reflection.

Electro-optically controlled switching and deflection in domain-engineered LiNbO 3

Abstract: We report a beam deflection technique that exploits electric-field controlled deflection and total internal reflection at the interface between two anti-parallel domains realized in a single crystal lithium niobate wafer. The LiNbO 3 z-cut sample was 500-µm-thick and was photolithographically patterned and poled by means of an applied electric field, in order to realize two adjacent regions of opposite domain orientation. The boundary between these domains should be very regular and free from residual stress, but in practice, a small residual index difference exists at the interface. An electric filed E z applied across the interface region, produces equal in magnitude, but opposite in sign, refractive index variations between the adjacent anti-parallel domains. For sufficiently large index variation, and for grazing incidence geometry, that is when the incidence angle is between 87° and 89°, we obtain a high efficient beam deflection. Furthermore, if the incidence angle approaches the limit angle, which is about 89°, the Total Internal Reflection (TIR) occurs, producing an abrupt beam switch from transmission to reflection, characterized with a theoretical 100% switching contrast. However, the residual interface stress generates significant Fresnel reflection from this interface at high grazing angles, limiting the switching contrast ratio achievable at 20 dB. We present data obtained for wavelengths of 632.8 nm and 4.5 m; at the latter wavelength we demonstrated the possibility to perform amplitude modulation faster than mechanical chopping, in a spectral region where no Pockels cells are available Keywords: Total internal reflection, Switching, Scanning, Electro-optic effect, Lithium niobate

Investigation on metal reflection coatings of free-space optical interconnect components with integrated fan-out DOEs

Abstract: We have designed a phase-only DOE with 1-to-9 beam fan-out functionality for optical beam distribution in an existing free-space optical interconnect (OI) component. However, due to the oblique angles of higher order diffracted beams, the condition of total internal reflection is not always met. To solve the problem, we propose to use an aluminum coating on top of the DOE and the deflecting prism sidewall. We compare experimentally a metal coated and uncoated replica of the OI component and investigate the polarization dependence of the reflectivity of the coating. We consider gold as a coating for future experiments, since the imaginary part of its complex index of refraction is smaller than aluminum’s and therefore a smaller fraction of the incident light will be absorbed.

Enhanced total internal reflection by an active medium

Abstract: Totally internal reflected beam can be amplified if the lower-index medium has gain. We examine the energy flux and the Goos Manchen shift for various cases.

Experimental verification of backward-wave phenomenon by observation of reflection at angles larger than 90° in an anisotropic medium

Abstract: Calcite with its principal axes coordinates at an angle of φ=45° from its surface normal is used here to observe the anomalous reflection at the calcite/air interface. Light is incident from the lateral side of the crystal to yield an angle of reflection larger than 90°. The reflected backward wave behavior is detected by observing the direction in which the light exits the crystal. Reflectance is calculated according to the nonsymmetric reflection theory.

Goos-Hanchen shift description in planar optical waveguides

Abstract: In this paper, using the Helmholtz wave equation and the tunneling time of a photon through an index of refraction barrier, the reflection delay time and reflection coefficient calculated and analytical expression for these quantities are introduced. It predicts that, the reflection delay time and coefficients depends on the refraction index, the thickness of barrier, the incident angle, and the incident wave frequency. Using these relations, we obtain the light penetration depths as well as horizontal shifts for reflection component of incident light to interface of two media. Our results completely describe the nature of Goos-Hanchen shifts in planar optical slab waveguides as a common device in optical integrated circuits (OIC). Also, the experimental data and our prediction completely close together.

Another kind of total reflection and the electromagnetic field in optical tunneling

Abstract: Another kind of total reflection is discussed, which takes place at a surface from optically thinner medium to optically denser medium in the tunneling process in a frustrated total internal reflection structure. It is shown that the tunneling energy flux in the tunneling process is the result of the interference between the incident and reflected waves. The multiple reflection expressions for the light waves in the tunneling and transmission regions are also presented.

About the mediums with unusual refraction and reflection laws

Abstract: It is noted, that recently the increased attention is attracted to the artificial media with negative refraction index, which are investigated in Russia since 1940, and that most interesting results are obtained in terms of isofrequences.

Time-differential Mijssbauer total external reflection of synchrotron radiation

Abstract: The effect of interference of nuclear resonant and electronic Rayleigh scattering is theoretically treated in time domain Mb 42.10

Metamaterials with ultralow index of refraction: properties and applications

Abstract: There has been a growing interest in the design and fabrication of composite materials to enhance the flexibility in specifying their optical properties for device applications. Here we show that metamaterials composed of metal-dielectric nano-structures can be engineered to have an effective refractive index below unity at optical wavelengths. These materials show intriguing optical properties including total external reflection. Different rigorous and approximate modeling techniques will be compared. We will show a novel approach to derive a realistic value of the effective refractive index from the reflection coefficients of finite slabs. The effect of losses and dispersion will be analyzed in the visible range of frequencies considering the properties of real metals. We explain the differences among ultra-low refractive index metamaterials, photonic bandgap materials, and metals. Finally, we propose the application of these metamaterials to waveguide structures that guide light in air by total external reflection.