Showing papers on "Total external reflection published in 1989"
TL;DR: In this paper, a general theory for the scattering of x rays from a single nonideal interface between two dielectric media is developed for arbitrary polarization and at all angles of incidence (measured from the normal) less than the critical angle for total external reflection.
Abstract: A general theory is developed for the scattering of x rays from a single nonideal interface between two dielectric media. It is then extended to describe the scattering of x rays from a multilayer structure composed of many nonideal interfaces. The most unique feature of this theory is that there are no constraints on the physical structure of the interfaces; the interfaces can have any form of roughness or compositional inhomogeneity. A simple analytical expression is derived for both the near and far radiation field to first order, assuming that the scattering is weak. The theory is valid for arbitrary polarization and at all angles of incidence (measured from the normal) less than the critical angle for total external reflection. Finally, the results are applied to study the effect of different interface structures on the performance of multilayer x‐ray optics.
228 citations
TL;DR: In this paper, the interface between a dielectric of high refractive index and the sample is taken as the reflecting surface, and a reflection spectrum of high contrast and intensity is obtained, which strongly resembles a transmission spectrum.
188 citations
TL;DR: In this paper, a new approach is proposed, based on considering the contribution of each bilayer to the extinction in a given stack of bilayers, and the discrete equations governing the choice of layer thicknesses are derived and solved.
Abstract: Multilayer structures, analogous to broadband optical filters, may be used to reflect X-rays or neutrons at angles larger than the total external reflection angle intrinsic to the bulk mirror material. These so-called supermirrors have generally been designed using continuum theories, which predict that the thickness of the jth layer in the multilayer should vary smoothly as j−1/4. A new approach is proposed, based on considering the contribution of each bilayer to the extinction in a given stack of bilayers, and the discrete equations governing the choice of layer thicknesses are derived and solved. In the limit of zero layer thickness, the continuum result is recovered. The design produces essentially perfect reflectivity over the entire supermirror range. An optimal technique for trading reflectivity to gain angular range also emerges naturally from the physics of the design.
110 citations
Patent•
19 Oct 1989
TL;DR: In this paper, a nearly index matched (NIM) optic is formed from at least two elements having indices of refraction that are substantially the same over a given range of wavelengths.
Abstract: A nearly index matched (NIM) optic is formed from at least two elements having indices of refraction that are substantially the same over a given range of wavelengths. The optical cell can have matched solid and fluid lenses in which the solid has at least one curved interface in contact with the fluid. The solid and fluid share a boundary with equal but opposite curvature at each point over the aperture of the NIM optic. The effective optical curvature of the boundary is reduced by the difference in the index of refraction between the two elements of the NIM optic. This difference in the index of refraction can be controlled by changing the index of refraction of at least one of the elements so as to change the difference in the index of refraction across the optical boundary.
88 citations
TL;DR: The local atomic structure surrounding uranium in borosilicate glass has been investigated by fluorescence x-ray absorption spectroscopy as discussed by the authors, which demonstrates that uranium occupies a uranyl-like environment that hydrates as leaching progresses.
Abstract: The local atomic structure surrounding uranium in borosilicate glass has been investigated by fluorescence x-ray absorption spectroscopy. By employing angles of incidence either side of the critical angle for total external reflection, surface and near-surface structure can be distinguished. The results of leaching in water at 100{degree}C have been examined in detail. Wet and dried glass surfaces can be differentiated. Analysis of glancing-angle spectra demonstrates that uranium occupies a uranyl-like environment that hydrates as leaching progresses. Uranyl complexing occurs in a planar geometry. The initial corrosion process can be readily understood by using the modified random network model for glass structure, which predicts diffusion of cations and water taking place via percolation pathways through the network. Following extended corrosion treatment, evidence for the formation of hydrated uranyl silicates that the surface has been found.
60 citations
TL;DR: In this article, the authors used a grazing incidence asymmetric Bragg geometry to obtain the depth-dependent structure of a nominally Fe2O3 thin film, which was oxidized from an Fe3O4 film.
Abstract: X‐ray depth profiling in a grazing incidence asymmetric Bragg geometry is used to obtain the depth‐dependent structure of a nominally γ‐Fe2O3 thin film, which was oxidized from an Fe3O4 film. As the incidence angle is varied from angles less than the critical angle for total external reflection to angles greater than the critical angle, the x‐ray penetration depth increases from about 20 to several thousand angstroms. The observed diffraction originates from this region of variable depth and a structural depth profile of the thin film can be obtained by measuring the diffraction pattern as a function of incidence angle. The iron oxide film is found to have a 45‐A‐thick surface layer of α‐Fe2O3; beneath this layer the film is predominantly γ‐Fe2O3 but also contains about 2.6 at. % α‐Fe2O3. These data, together with previous chemical and magnetic data, suggest that during oxidation of the Fe3O4 film the surface layer forms by the outward diffusion of Fe ions and their subsequent oxidization to α‐Fe2O3. One ...
26 citations
Patent•
22 Sep 1989TL;DR: In this paper, a method for monitoring the refractive index of an optical film as it is being deposited on a substrate is presented, where the film is illuminated by a source of light at a wavelength that is outside and less than the reflectance band of the coating.
Abstract: A method is provided for monitoring the refractive index of an optical film as it is being deposited on a substrate. The film is illuminated by a source of light at a wavelength that is outside and less than the reflectance band of the coating. If the refractive index of the film is initially matched to the refractive index of the substrate and has no abrupt changes in its gradient-index profile, reflectance from the surface of the film can be detected and measured. In the absence of interference fringing from internal reflections, surface reflectance of the interface of the film with the surrounding air or vacuum is closely related to the refractive index of the film at its surface. Thus, surface reflection is monitored to provide a control signal to the deposition apparatus to conform the refractive index of material being deposited to a predetermined refractive index profile specified for the desired optical film.
13 citations
TL;DR: In this paper, the angular distribution of the reflected light at the interface between two transparent dielectric media is analyzed to estimate the mean extension of the polymer perpendicular to the interface and its mean extension parallel to it.
Abstract: A new method for studying the properties of adsorbed polymer molecules is proposed. If polymer molecules are adsorbed on the low refractive index side of an interface between two transparent dielectric media, they can scatter the evanescent radiation generated by total internal reflection of light incident on the interface from the high refractive index medium. Analysis of the angular distribution of the scattered light yields information about the mean extension of the polymer perpendicular to the interface and its mean extension parallel to the interface. As an example, the theory is illustrated for the case of rods, anchored at one end to the interface, and with uniform angular distribution in the half space of the low refractive index medium. Both analytical and numerical analyses are presented.
11 citations
TL;DR: The local atomic structure surrounding uranium in borosilicate glass has been investigated by fluorescence x-ray absorption spectroscopy as mentioned in this paper, which demonstrates that uranium occupies a uranyl-like environment that hydrates as leaching progresses.
Abstract: The local atomic structure surrounding uranium in borosilicate glass has been investigated by fluorescence x-ray absorption spectroscopy. By employing angles of incidence either side of the critical angle for total external reflection, surface and near-surface structure can be distinguished. The results of leaching in water at 100{degree}C have been examined in detail. Wet and dried glass surfaces can be differentiated. Analysis of glancing-angle spectra demonstrates that uranium occupies a uranyl-like environment that hydrates as leaching progresses. Uranyl complexing occurs in a planar geometry. The initial corrosion process can be readily understood by using the modified random network model for glass structure, which predicts diffusion of cations and water taking place via percolation pathways through the network. Following extended corrosion treatment, evidence for the formation of hydrated uranyl silicates that the surface has been found.
7 citations
TL;DR: In this article, a specially designed goniometer has been used to study dynamical x-ray diffraction in a nearly perfect germanium crystal under total external reflection conditions, showing unusual features arising from the excitation or deexcitation of the wave fields in shallow surface layers of the bulk crystal.
Abstract: Synchrotron radiation obtained from the 6‐T vertical‐wiggler source at the Photon Factory has been used to study dynamical x‐ray diffraction in a nearly perfect germanium crystal under total external reflection conditions. A specially designed goniometer has allowed independent control of the glancing angle and the deviation angle from exact Bragg incidence. The rocking‐curve profiles observed from slightly asymmetric Bragg planes as a function of glancing angle were found to be quite different for both the diffracted and specular beams. These profiles show unusual features arising from the excitation or de‐excitation of the wave fields in shallow surface layers of the bulk crystal. Furthermore, GeK fluorescence signals measured during the Bragg reflection showed characteristic modulations, demonstrating the feasibility of new standing‐wave experiments for determination of interface structures.
3 citations
TL;DR: In this article, the problem of reflection of light from the surface of an amplifying corrugated waveguide is solved, and an increase in the waveguide gain increases considerably the reflection coefficient and reduces the spectral width of the reflection peak.
Abstract: The problem of reflection of light from the surface of an amplifying corrugated waveguide is solved. An increase in the waveguide gain increases considerably the reflection coefficient and reduces the spectral width of the reflection peak.
TL;DR: In this article, the authors used total external reflection and fluorescence detection for the Al/GaAs system and showed that only moderate interdiffusion of Al into the GaAs substrate was observed.
Abstract: Reflection EXAFS experiments, using total external reflection and fluorescence detection, have been performed for the Al/GaAs system. Our preliminary EXAFS results imply only moderate interdiffusion of Al into the GaAs substrate. Technical aspects of the technique are also discussed, such as methods to minimize diffraction-peak contamination of the data.
TL;DR: In this paper, dynamical x-ray diffraction using standing wavefields (XSW), kinematical surface diffraction (KSD), Fresnel reflection (FR), and absorption spectroscopy (SEXAFS, SXANES) are combined to form new methods such as diffraction of evanescent x rays during total external reflection (DEXTER) and reflection EXAFS (this paperLEXAFs).
Abstract: Structural studies of interfaces with synchrotron x‐radiation (SXR) are presently carried out with several different methods which were developed in connection with SXR over the past decade: dynamical x‐ray diffraction using standing wavefields (XSW), kinematical surface diffraction (KSD), Fresnel reflection (FR), and absorption spectroscopy (SEXAFS, SXANES). These methods can determine different, and often complementary parameters of a system such as short‐/long‐range order, relaxation relative to bulk, structure normal/parallel to surface, valence state of surface atoms, roughness of a buried interface, etc. Accordingly, these different principles have also been combined to form new methods such as diffraction of evanescent x rays during total external reflection (DEXTER) and reflection EXAFS (REFLEXAFS). It is, therefore, highly desirable to have the opportunity to study the same interface system with different methods. On the other hand, preparation of a system in ultrahigh vacuum requires in most cas...
TL;DR: Mesure du rendement photoelectronique sous des conditions de diffraction dynamique, sous incidence rasante sur du silicium ayant les plans (111) paralleles a la surface as mentioned in this paper.
Abstract: Mesure du rendement photoelectronique sous des conditions de diffraction dynamique sous incidence rasante sur du silicium ayant les plans (111) paralleles a la surface. Dependances angulaires, experimentale et calculee, du coefficient de reflexion de l'onde diffractee
TL;DR: In this article, a numerical method to calculate the instrumental resolution function at any diffraction conditions is proposed, where the resolution is calculated as a function of the wavelenght and the divergence of the primary beam.
TL;DR: In this article, the authors consider the problem raised by a microscopic interpretation of the refractive index and study the reflection of a plane wave, in the dipolar approximation, and show that a macroscopic description may be recovered to very good approximation when an 'apparent' this article index is introduced, related to both the local polarisability and its gradient.
Abstract: Optical techniques are widely used to study thin layers and more generally interfacial structures. The authors consider the problem raised by a microscopic interpretation of the refractive index and study the reflection of a plane wave, in the dipolar approximation. They describe microscopically the reflection on a layered interface. It is shown that a macroscopic description may be recovered to very good approximation when an 'apparent' refractive index is introduced. This index is related to both the local polarisability and its gradient. The 'p' wave requires two such indexes, the direction of the gradient being specific. Comparison is established with the Lorentz refractive index profile. In a second part the excess of local field on the interface is computed, and this is applied to study the vicinity of the Brewster incidence.