Showing papers on "Total external reflection published in 2011"

Debye–Scherrer rings from block copolymer films with powder-like order

Abstract: The powder-like orientation of lamellar domains in thin films of the diblock copolymer polystyrene-block-poly(methyl methacrylate) is investigated using grazing-incidence small-angle X-ray scattering (GISAXS) and grazing-incidence small-angle neutron scattering (GISANS). Conventional monochromatic GISANS and GISAXS measurements are compared with neutron time-of-flight GISANS. For angles of incidence and exit larger than the critical angle of total external reflection of the polymer, Debye–Scherrer rings are observed. The position of the Debye–Scherrer rings is described quantitatively based on a reduced version of the distorted-wave Born approximation. A strong distortion of the ring shape is caused by refraction and reflections from the film interfaces. Close to the critical angle, the ring shape collapses into a banana shape.

Total reflection X-ray fluorescence analysis: Physical foundations and analytical application (A review)

Abstract: The current state of the art in one of the most promising techniques of X-ray spectral analysis, namely, total reflection X-ray fluorescence analysis (TXRF), is summarized. The underlying physical processes, including reflection, refraction, total external reflection (TER) of X-rays, and formation of standing waves by TER, are considered. The construction and crucial components of a modern energy-dispersive TXRF spectrometer, involving X-ray tubes, monochromators, detectors, and reflectors, are described. Examples of analytical application of TXRF are given. High efficiency of this technique for qualitative and quantitative chemical analysis of liquids and solids of various natures is demonstrated. The main research trends in surface analysis and investigation of surface layers of solids by TXRF are discussed.

Total internal reflection based sub-wavelength grating sensor for the determination of refractive index of liquids

Abstract: In this work we present an optical refractive index sensor based on the Grating Light Reflection Spectroscopy (GLRS) method. The sensor consists of the finely spaced diffraction grating (sub micrometer region) that is in contact with the analyte (liquid or gas). Shining the polarized polychromatic light on the grating at the threshold angles of incidence and analysing the spectral response of the specular reflection we have observed steep changes of the reflection coefficient at certain wavelength values. We have shown that for the liquid analytes specular reflection spectra demonstrate double peak that can be used as one more parameter in the spectroscopic measurements. The detailed analysis of the spectral composition of the specular reflection illustrates ability of control of refractive index of analyte at least for two wavelengths at constant angle of incidence.

Total internal reflection and evanescent gain

Abstract: Total internal reflection occurs for large angles of incidence, when light is incident from a high-refractive-index medium onto a low-index medium. We consider the situation where the low-index medium is active. By invoking causality in its most fundamental form, we argue that evanescent gain may or may not appear, depending on the analytic and global properties of the permittivity function. For conventional, weak gain media, we show that there is an absolute instability associated with infinite transverse dimensions. This instability can be ignored or eliminated in certain cases, for which evanescent gain prevails.

Index of refraction of shock-released materials

Abstract: A new technique to measure the refractive index of shocked materials is reported. The arrival of a transparent shock at the free surface of an optical window generates a discontinuity in the observed interferometry record. In this work, we show that the magnitude of that discontinuity is simply defined by the shock velocity, the shocked refractive, and the free-surface velocity. This new technique, to measure the high-pressure refractive index of a transparent material, is demonstrated.

Damage threshold of amorphous carbon mirror for 177 eV FEL radiation

Abstract: We present results of damage studies performed at the Free-Electron LASer in Hamburg (FLASH) on amorphous carbon (a-C). The experiment was performed in the total external reflection geometry representing the working configuration of X-ray mirrors. The 177 eV photon laser beam was focused on a 40 nm thin layer of a-C coated on a silicon substrate. Single-shot damages were produced at two different grazing angles (4.3° and 7.7°) below the critical angle (θc=8°) calculated for this photon energy. The corresponding damage fluence thresholds were determined to be 43.7 and 74 mJ/cm2. No evidence of delamination or mechanical damages (cracks) under grazing angles on the 40 nm thin sample was observed. The results are compared with the results of the previous experiment done on thicker layers (900 nm) of a-C with the same experimental conditions

X-ray diffracted intensity for double-reflection channel-cut Ge monochromators at extremely asymmetric diffraction conditions

Abstract: The width and integrated intensity of the 220 X-ray double-diffraction profile and the shift of the Bragg condition due to refraction have been measured in a channel-cut Ge crystal in an angular range near the critical angle of total external reflection. The Bragg angle and incidence condition were varied by changing the X-ray energy. In agreement with the extended dynamical theory of X-ray diffraction, the integrated intensity of the double diffraction remained almost constant, even for the grazing-incidence condition very close to the critical angle for total external reflection. A broadening of the diffraction profile not predicted by the extended theory of X-ray diffraction was observed when the Bragg condition was at angles of incidence lower than 0.6°. Plane wave topographs revealed a contrast that could be explained by a slight residual crystal surface undulation of 0.3° due to etching to remove the cutting damage and the increasing effect of refraction at glancing angles close to the critical angle. These findings confirm that highly asymmetric channel-cut Ge crystals can also work as efficient monochromators or image magnifiers at glancing angles close to the critical angle, the main limitation being the crystal surface preparation.

Negative Refraction Angular Characterization in One-Dimensional Photonic Crystals

Abstract: Background Photonic crystals are artificial structures that have periodic dielectric components with different refractive indices. Under certain conditions, they abnormally refract the light, a phenomenon called negative refraction. Here we experimentally characterize negative refraction in a one dimensional photonic crystal structure; near the low frequency edge of the fourth photonic bandgap. We compare the experimental results with current theory and a theory based on the group velocity developed here. We also analytically derived the negative refraction correctness condition that gives the angular region where negative refraction occurs. Methodology/Principal Findings By using standard photonic techniques we experimentally determined the relationship between incidence and negative refraction angles and found the negative refraction range by applying the correctness condition. In order to compare both theories with experimental results an output refraction correction was utilized. The correction uses Snell's law and an effective refractive index based on two effective dielectric constants. We found good agreement between experiment and both theories in the negative refraction zone. Conclusions/Significance Since both theories and the experimental observations agreed well in the negative refraction region, we can use both negative refraction theories plus the output correction to predict negative refraction angles. This can be very useful from a practical point of view for space filtering applications such as a photonic demultiplexer or for sensing applications.

Grazing incidence optics for X-ray astronomy

Abstract: Cosmic X-ray sources are usually very weak and their detection, therefore, needs large area telescopes to gather light and sensitive detectors to enhance quantum efficiency. Conventional telescopes for visible light use refracting or reflective optics which is impractical for X-ray wavelengths because photon energies are greater than the binding energies of the typical atomic electrons leading to a refractive index for X-rays being less than unity. Thus single surface reflectivity for near-normal incidence is negligible for X-rays. However, by Snell’s Laws, total external reflection occurs and X-rays can be reflected from a surface up to a critical angle (usually about a degree for energies below 10 keV) given by cosine θ = n. This is known as the grazing angle. X-ray telescopes are made to exploit the grazing incidence from a set of co-axial and con-focal shells of paraboloidal and hyperboloidal mirrors. X-ray reflectors having high atomic number surfaces with low scattering are used to realize imaging capability for a telescope. I describe here various configurations required, and the various technologies used and their limitations, to make practical X-ray telescopes. A soft X-ray imaging telescope (SXT) using grazing incidence has been built at TIFR for ASTROSAT—an Indian Multiwavelength Satellite designed to cover a very broad band of X-rays, UV and optical. Astrosat is planned to be launched by a Polar Satellite Launch Vehicle in 2012 into a near-Earth Equatorial orbit. I will also describe the ongoing R&D for realizing telescopes for hard X-rays above 10 keV useful for both Astronomy and medical diagnostics.

Study of Positive and Negative Refraction of Visible Light at the Cu/Air Interface

Abstract: Light transmission at the Cu/air interface was measured in the visible region for a series of wedge-shaped Cu film samples. It is found that light refraction at the Cu/air interface changes from negative in the Drude region, passing through zero at about Eg, to positive in the interband-transition region. Detailed discussion is given to exclude those mechanisms which have been arguably assigned as the cause of negative refraction at a metal/dielectric interface. Based on the spectra of the measured refractive index and modeled in the Drude region, the positive and negative refraction analyzed in this work are qualitatively in agreement with dispersion of the group refractive index, and may aid in understanding light transmission at the metal/dielectric interface as characterized by the law of refraction.

Near field lens i.e. meta-material lens, for use in optical assembly for focusing electromagnetic waves with frequencies in e.g. UV region, has cooling medium exhibiting refraction index that is reverse-variable on output value

Abstract: The lens (20) has two plasmon support sections (22, 24) arranged at a coupling medium (26) such that plasmons on one of the sections are excitable by excitation of plasmons on the other section. The medium is formed such that that the medium exhibits refraction index for utility-light (34). The refraction index is varied for changing focus of a near field (36) by irradiated control light (32) locally from an output value to a deviating value, and the refraction index is reverse-variable on the output value. The sections are made of metallic material e.g. silver or gold. The coupling medium comprises components e.g. organic molecules or molecule groups.

Optical recording medium, manufacturing method for optical recording medium

Abstract: The present disclosure relates to an optical recording medium and a manufacturing method for an optical recording medium capable of obtaining an appropriate reproduction signal, as a bar code-shaped recording region (BCA) on an optical recording medium. This recording region (BCA) is provided that includes high reflection rate regions and low reflection rate regions which appear alternately in the track line direction, and each of the high reflection rate regions and the low reflection rate regions is formed to be continuous in the track pitch direction, whereby a bar code-shaped reflection pattern is formed, and information is recorded with the reflection pattern. In the BCA, the low reflection rate region is formed with pit strings. The high reflection rate region and the low reflection rate region are formed to satisfy: S+M/2≦0.6H, where a signal level of a reproduction signal obtained from a reflection light in the high reflection rate region is denoted as “H”, a signal level of a reproduction signal obtained from a reflection light in the low reflection rate region is denoted as “S”, and a degree of modulation of the reproduction signal obtained from the reflection light in the low reflection rate region is denoted as “M”.

Reflected wave atypical phase change at a boundary

Abstract: According to Fresnel formulae, at normal incidence on an abrupt interface, the reflected wave has a phase difference of zero or π, if the second medium has a lower or larger refractive index than the first. However, what happens if the refractive indices of two media are the same at the interface but the derivative of the refractive index varies abruptly? Since the two media are not homogeneous because the refractive index derivative is finite, the problem cannot be tackled with the Fresnel formalism. In order to deal with this problem the amplitude and phase representation of plane electromagnetic waves is used. An invariant is obtained that permits the decoupling of the amplitude and phase equations, both of which, are nonlinear. The amplitude equation is then solved numerically. No approximations are made regarding how slow or fast refractive index varies compared to the wavelength. Interpretation of the amplitude equation solutions reveal that surfaces where any of the derivatives of the refractive index profile is discontinuous, do enhance reflection. At normal incidence, the reflected wave thus generated will have a phase difference that may be a multiple of π/2, apparently contradicting the Fresnel equations.

An ‘electromagnetic wiggler’ originating from refraction of waves at the side edge of a Bragg reflector

Abstract: Calculations are reported which predict that light incident on the side edge of a Bragg reflector can show varied and unusual refraction behaviour, including a rapid transition from positive to negative refraction. Although under certain conditions negative refraction can occur, it is concluded that perfect lensing based on it is unlikely to be realised in practice. However, it is shown that light incident obliquely on the structure can be made to propagate normal to the interface after refraction while exhibiting lateral oscillations of its Poynting vector, an effect that could possibly find application in an ‘electromagnetic wiggler’. It is also shown that negative group velocity rather than negative effective mass is required for the observation of the negative refraction, and in the case of low refractive index contrast, negative refraction occurs only when the size of the illumination spot exceeds a critical value, which is inversely proportional to the contrast of the refractive indices.

Polarization and angle-of-incidence dependence of the Goos–Hänchen shift in total internal reflection at a planar dielectric–dielectric interface

Abstract: The Goos–Hanchen shift (GHS) that accompanies total internal reflection (TIR) of a monochromatic p- or s-polarized light beam at a planar interface between a dense medium of incidence of refractive index and a rarer medium of refractive index is considered as a function of the index ratio, , and angle of incidence, . At a unique incidence angle the GHS is the same for the p and s polarizations, hence the shift becomes independent of polarization. Other significant characteristics associated with TIR at the special angle are identified. It is also shown that the GHS is nearly independent of in the range if the incident light is s-polarized and the index ratio N > 2.5. No comparable results are obtained for incident p-polarized light.

Total Reflection Through Effect of Light in 1D Photonic Crystal

Abstract: The transition matrix method was adopted,and the transmissivity of TE wave and TM wave were analyzed when incident angle greater than full reflection angle,to study the total reflection through effect of light in one-dimensional(1D) photonic crystal.The total reflection through effect was found in the transmission wave.Response curves of the through effect versus incident angle,response curves of the through effect versus wavelength,and response curves of the through effect versus medium thickness were obtained.Total reflection through effect of light in 1D photonic crystal was also explained by the theories of quantum and evanescent wave.

Method for remotely measuring fluctuations in the optical index of refraction of a medium

Abstract: A method is provided for remotely measuring index of refraction fluctuations. From a first location, an optical beam is focused at a focal plane located at a second location in a medium of interest. As a result, a beam of energy is backscattered towards the first location. At the first location, a size of the backscattered beam is determined where the size is indicative of strength of fluctuations in the medium's index of refraction.

Features of optical spectral-selective elements characteristics with the increased value of refraction index

Abstract: In report modeling of characteristics of optical spectral-selective elements of the cylindrical form with the increased value of the refraction index, using effect of light scattering is organized. As have shown results of researches, application of cylindrical optical element for spectral angular selection is limited. At increase in value of refraction index the optical element starts to function in a mode of quasi uniform light scattering.

Method for measuring dielectric loss by utilizing pulse response time of electromagnetic evanescent wave irradiance

Abstract: The invention provides a method for measuring dielectric loss by utilizing pulse response time of electromagnetic evanescent wave irradiance. The method comprises the following steps of: 1) determining a real part of the refractive index of a medium to be measured in electromagnetic wave with preset frequency range, and defining the medium to be measured to be an optically thinner medium; 2) seeking an optically denser medium with known refractive index and the real part of the refractive index greater than that of the medium to be measured, and forming a total reflection system by the optically denser medium and the medium to be measured; 3) emitting the electromagnetic wave with preset frequency range from the optically denser medium to the medium to be measured, and adjusting the incident angle to realize the total reflection of the electromagnetic wave to at an interface of the optically denser medium and the medium to be measured and generate evanescent wave inside the medium to be measured; and 4) adjusting the power of the incident electromagnetic wave to generate little pulse, measuring the response time of the evanescent wave irradiance to the pulse, and calculating an imaginary part of the refractive index of the medium to be measured according to the pulse response time. The measuring method not only can be carried out repeatedly in a lossless way, but also can realize the measurement with ultra-high precision.