Showing papers on "Total external reflection published in 1998"

Engineered omnidirectional external-reflectivity spectra from one-dimensional layered interference filters.

Abstract: Owing to optical refraction, external rays that are incident upon a high-refractive-index medium fall within a small internal cone angle. A one-dimensionally periodic Bragg structure can reflect over an angular acceptance range that is greater than the small internal refraction cone, if the internal refractive-index contrast is sufficient. Thus Winn [Opt. Lett. (to be published)] charted the range of refractive indices at which omnidirectional external reflection occurs. A wide spectral gap requires a high-index contrast. It is proposed that, by chirping or grading the periodicity of the structure, one can cover an arbitrarily wide spectral range with only a modest index contrast and, furthermore, that arbitrary spectral shapes can be produced. The graded-periodicity approach requires only a modest index contrast, provided that the average refractive index is >2.

Thin film dichroic color separation filters for color splitters in liquid crystal display systems

Abstract: An optical filter is provided for use in color projection display imaging systems which utilize liquid crystal light valves for image modulation. The optical filter is a dichroic coating which separates light into different colors. The optical filter is located on a light transmissive surface of a color splitting device such as a Philips prism. The optical filter is formed from layers of at least two different dielectric materials including a high refractive index material, such as zirconium oxide and a low refractive index material such as aluminum oxide. The low refractive index material has an average refractive index of no less than about 1.6. The high refractive index material has an average refractive index which is sufficiently greater than the average refractive index of the low refractive index such that the average refractive index of the high refractive index material divided by the average refractive index of the low refractive index material yields a ratio that is greater than about 1.2 and less than about 1.55.

Dewetting of Thin Polymer Films: an X-ray Scattering Study

Abstract: The surface morphology of different dewetting states of thin polymer films (polystyrene) on top of silicon substrates was investigated. With diffuse X-ray scattering in the region of total external reflection a high in-plane resolution was achieved. We observe a new nano-dewetting structure which coexists with the well known mesoscopic dewetting structures of holes, cellular pattern and drops. This nano-dewetting structure consists of small dimples with a diameter in the nanometer range. It results from the dewetting of a remaining ultra-thin polymer layer and can be explained with theoretical predictions of spinodal decomposition. The experimental results of the scattering study are confirmed with scanning-force microscopy measurements.

Measurements and analysis of radiation effects in polycapillary x-ray optics

Abstract: Polycapillary x-ray optics are arrays of large numbers of small hollow glass tubes which deflect x rays by successive total external reflection. These optics have growing numbers of applications in areas ranging from medical imaging to microanalysis. An accelerated radiation effects study has been performed to understand the performance limitation of these optics for medium to high intensity radiation applications, to study x-radiation damage mechanisms, and to investigate possible ways to mitigate the radiation effects on x-ray transmission efficiency. Exposures have been done in white beam bending magnet radiation with peak energies at 5 and 11 keV and focused broad band radiation centered at 1.4 keV. In situ and ex situ measurements of loss of x-ray transport efficiency have been executed at doses up to 1.8 MJ/cm2. Thin polycapillary fibers displayed noticeable bending and experienced substantial degradation of x-ray transmission. Thicker polycapillary fibers showed a linear but much slower transmissio...

X-ray Optics for Synchrotron Radiation; Perfect Crystals, Mirrors and Multilayers

Abstract: The X-ray optical properties of mirrors and Bragg reflecting perfect crystals are almost perfectly matched to the characteristics of synchrotron-radiation sources. That the X-ray refractive index is close to but less than one was realised early in the history of X-ray scattering – consequences are that mirrors exhibit total external reflection over a small angle range, ca 0.01 rad, and perfect crystals totally reflect X-rays in a small angle range, ∼ a few seconds of arc near the Bragg angle. The theory and application of these unique properties was developed in considerable detail in the three decades before the advent of the synchrotron-radiation era. This historical development is traced with special emphasis on the way in which the optical concepts were then straightforwardly applied to synchrotron-radiation X-ray optical design. In more recent times, the technology of synthetic multilayers has been developed so that these too are widely used in X-ray optics for synchrotron-radiation beamlines. As X-ray synchrotron-radiation sources were born, perfect-crystal X-ray optics and crystal-growth technology matured; this symbiosis was not planned, it could not have been planned … but it works, spectacularly!

Surface effects in displacive phase transformations studied by X-ray specular reflectivity

Abstract: We report the first application of specular reflectivity to measure the formation of surface relief resulting from displacive phase transformations. It is demonstrated for the martensitic transformation of Ni62.5Al37.5 and the two step transformation of Ni2MnGa that reliefs heights ranging from the nanoscopic to the mesoscopic scale can be characterized by reflectivity experiments. Since a mesoscopic surface relief shows up as a dip below the critical angle, this opens up the opportunity to study displacive phase transitions at the intensity level of total external reflection. The application of the technique to surface nucleation problems is discussed.

Internal reflection of one-dimensional bright spatial solitons

Abstract: We study the reflection of one-dimensional spatial solitons at the non-linear interface between a Kerr-type medium and a linear medium. Our study places emphasis on determining the physical conditions under which the beam reflected by the non-linear interface is still a spatial soliton. We find that for small angles of incidence an elastic internal reflection takes place, in the sense that the reflected soliton is essentially the same as the incident one. For incidence angles near a critical angle, the reflected soliton becomes less intense and its reflection angle is smaller than the angle of incidence. Finally, for spatial solitons with input angles well above the critical angle, the main part of the energy is transmitted to the linear medium, and no soliton is internally reflected.

Low reflection film and display panel using it

Abstract: PROBLEM TO BE SOLVED: To obtain a practical reflection index of an incident reflection angle with wide visibility by adjusting and forming thickness of each layer of a low reflection film so as to be below a given reflection index. SOLUTION: Thickness of each layer of a low reflection film is, for example, about 20 nm in a first ITO thin film, about 25 nm in a first silicon dioxide thin film, about 45 nm in a second ITO thin film, and about 100 nm in a second silicon dioxide thin film. As a result, the spectroscopic reflection index becomes 1% or less when a light beam with the wavelength range of 490 to 640 nm for a light beam incident angle of 10 degrees. Further, for the incident angle of 10 degrees the reflection index up to a wavelength of 650 nm of the incident light beam is 1% or less, the reflection index up to a wavelength of 700 nm is 1.6% or less, and the reflection index up to a wavelength of 750 nm is 2.7% or less. Spectroscopic reflection index characteristics in which a value (y) for the reflection light degree of color is 0.10 or more and 0.25 or less is obtained when the wavelength range of the incident light beam for of the light beam incident angle of 10 degrees is 380 to 780 nm.

Measurement and accuracy analysis of refractive index using a specular reflectivity close to the total internal reflection

Abstract: A new method to measure refractive index and the accuracy analysis as well is presented. The characteristic includes that the direction of incident light is not perpendicular to the interface but close to the critical angle of total internal reflection. That the specular reflectivity changes sharply near the critical angle implies that a high measuring sensitivity be reached easily. A narrow p- polarized laser beam and a prism or a quasi-semi-cylindrical lens in contact with a sample are applied in the apparatus. In order to match a high accuracy, a photoelectronic receiver with dual-channel divider is designed to compensate the stability of output of laser. One of the advantages of the method is its high accuracy. The uncertainty in the refractive index measurement is in the fourth decimal place at least. The exact direction of incident laser beam depends on the accuracy of result expected. Another outstanding advantage is its particularly straightforward in use experimental techniques. The method will be the most promising tool to study the response of refractive index to subtle changes of different conditions.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Double-crystal diffractive modulator of synchrotron radiation

Abstract: The efficiency of time-modulation of synchrotron radiation by a double-crystal monochromator periodically curved by pulsed surface acoustic waves has been studied both experimentally and theoretically. It has been shown that the efficiency of such a system is significantly higher as compared to x-ray modulation by surface acoustic waves applied to x-ray mirrors—that is under the conditions of total external reflection. Possible modifications and improvement of a synchrotron radiation double-crystal diffractive modulator are discussed. The experiments were done at the diffraction beamline at the Brazilian National Synchrotron Light Laboratory (LNLS).

Reflection and Refraction of Bulk Waves

Abstract: When an incident bulk wave interacts with an interface, such as the boundary between a fluid and a solid, as found in immersion testing, both reflected and transmitted bulk waves are generated. Chapter 6 describes general properties of reflected and refracted waves for the case when a planar wave is incident on a plane interface. In the process a variety of concepts are introduced, such as acoustic impedance, Snell’s law, critical angles, pulse distortion, and inhomogeneous waves.

Analysis-material verifying element

Abstract: PROBLEM TO BE SOLVED: To make it possible to form inexpensive element, which is easy for activation and can form the mark having high visibility, by selecting the thickness and the reflectivity of a reflection preventing film so that the reflection of at least one wavelength of visible light becomes minimum by interference. SOLUTION: One layer or a plurality of layers of reflection preventing films are formed on the surface of the thin film or gel-shaped base material comprising quartz, plastics, metal and the like in a pattern shape or wedge shape by a blowing method or the like, and covalent bonding or adsorption is performed. Then, receiving material is attached on the uppermost layer of a reflection preventing film in correspondence with the object material to be analyzed. The refractive index of the base material is made to be approximately equal to the square of the refractive index of the material directly on the base material. Furthermore, the reflection preventing layer has the refraction index of the square root of the product of the refractive index of the base material and the refractive index of atmosphere or the value close to the square root and has the optical thickness of 1/4 of the wavelength of the light, whose reflection is to be measured, or the odd-number times of 1/4. Thus the mark, which has the excellent sensitivity and the more clear color or saturation of the contrast can be generated.

Structural characterization of surfaces and interfaces of materials by applying x-ray total external reflection phenomena

Abstract: An in-house grazing incidence x-ray scattering (GIXS) apparatus has been newly developed for characterizing the surface structure at a microscopic level. Using this apparatus, surface diffraction profiles from the oxidized SUS304 stainless steel were measured in the vicinity of the critical angle with the GIXS geometry. The depth profile was discussed from the integrated intensities of both oxidized phase and stainless steel bulk. An in-house grazing x-ray reflection apparatus (GXR) has also been newly built for studying the liquid surface, and the liquid/solid and liquid/liquid interfaces. This system was tested by measuring x-ray reflectivity profiles from free surface of mercury and the water/mercury interface. In addition, a new method has been proposed for determining the atomic number density of a near-surface element in materials using grazing x-ray reflection and anomalous dispersion effect. The essential equations for analyzing the measured reflection data were given and the capability of this anomalous grazing x-ray reflection (AGXR) method was well-confirmed by obtaining the atomic number densities of near surface elements with some selected examples of ZrO 2 -Y 2 O 3 crystal and the passivated stainless steel.

Nonlinear reflection of extremely short light pulses

Abstract: The reflection of intense laser pulses consisting only of several light field cycles from nonlinear, isotropic and transparent dielectric media is theoretically investigated. It is shown, that the spectrum of the reflected pulse is enriched by odd harmonics and at close linear refraction indices of bordering media the duration of the reflected pulse can become less significant than the duration of incident pulse. It is shown, that the intense refracted wave has a strongly asymmetrically broadened spectrum in nonlinear medium.

Solar collector retaining high incident solar radiation temperature

Abstract: The solar collector has at least two collector components (1,2) with different refractive indices, the component (2) with the lesser refractive index enclosing the component (1) with the higher refractive index, for preventing exit of the incident light by total internal reflection. The trapped solar radiation is fed to a load (5) via an optical conductor coupled to the component with the higher refractive index via an optical coupler with a reduced cross- section.

Bragg telescopes in lobster-eye configuration

Abstract: In this paper will be investigated the possibility to exploit the Bragg diffraction from mosaic crystals as a reflection technique for the realization of lobster-eye telescopes for hard x-rays In particular for our study we will assume the particular lobster-eye configuration also known as Schmidt imager This geometry is particularly interesting not only why it can allow a 1D focusing over large fields of view but also because it is relatively easy to be realized, being based on flat reflectors Until now lobster-eye telescopes have been mostly studied for applications in the classical x-ray band, making use of total external reflection at grazing angles mirrors However, due to the much larger reflection angles typical of Bragg diffraction it is possible to extend the use of the Schmidt geometry also to the hard x-ray energy band Here, in addition to a general description of the behavior of Schmidt telescopes based on the Bragg diffraction technique, we will report also some theoretical evaluations about the performances achievable with these devices

On a characteristic feature of grazing-incidence nuclear monochromators for synchrotron radiation

Abstract: It is shown theoretically that the optimum resonance monochromatization of synchrotron radiation by means of grazing-incidence antireflection mirrors is obtained not at the maximum possible enrichment (∼100%) but rather with a low enrichment in the Mossbauer isotope (the natural abundance in the case of iron) This possibility is due to the fact that the conditions of interferometric suppression of electron reflection in the range of total external reflection angles is uniquely sensitive to small variations of the film or substrate density

A new technique for measuring nonlinear refractive index

Abstract: Summary form only given. The reflection Z-scan technique was recently suggested for the study of nonlinear effects in absorbing materials. This technique allows us to measure the modification in the reflection coefficient of a nonlinear material and to evaluate n, and /spl beta/ from this change. It is less sensitive than the transmission Z-scan technique because the beam distortion caused by the surface reflection is much smaller than the one caused by the transmission through the whole volume of the material. To overcome this small sensitivity, we suggest the use of a polarized incident beam close to Brewster angle. In this case the relative change in the reflection coefficient is increased due to the reduction in the linear term of reflection.

Time-resolved fluorescent X-ray interference.

Abstract: A fluorescent X-ray interference method can effectively measure nanometer-level conformational changes for non-crystallized molecules and proteins in aqueous conditions. The time-resolved technique can be used to obtain information about the dynamics of molecules and proteins. Instrumentation for time-resolved fluorescent X-ray interference has been designed. A typical interference-fringe pattern was observed with approximately 3 s of X-ray exposure time from K-fluorescent X-rays emitted from a Zn monoatomic layer on an Rh substrate. The primary X-ray beam was polychromed with a mirror for total external reflection of X-rays and was tuned to an energy level at which only Zn K radiation became optimally excited. The glancing angle of the primary X-ray beam was fixed at a glancing angle at which the total intensity of K-fluorescent X-rays emitted from Zn atoms corresponded to the maximum value. The fluorescent X-ray interference fringes were monitored with an imaging plate (IP) as a non-energy-dispersive two-dimensional detector. The exposed interference fringes on the IP were integrated along the direction of the fringes. The integrated fringes were in close agreement with a theoretical estimate based on the interference among transmitted and reflected waves at interfaces in the sample.