Showing papers on "Total external reflection published in 1987"

Evanescent absorption in kinematic surface Bragg diffraction.

Abstract: The Bragg scattering excited under the conditions of total external reflection is discussed within a kinematic approach based on the distorted-wave approximation. Due to evanescent absorption at grazing angles the maximum of the interference function of the surface Bragg reflection is displaced into the vacuum by an amount determined by the mean electron density of the medium. X-ray scattering experiments performed on a mosaic single crystal with synchrotron radiation confirm the predictions of the kinematic theory and indicate the potential for obtaining structural information on the first atomic layers.

Spectral filter with integral antireflection coating

Abstract: A gradient index filter can be fabricated with integral antireflection properties without degrading the inband performance of the filter. The filter is for placement between an incident medium and a substrate to reflect incident electromagnetic energy having wavelengths within a predetermined band of wavelengths and to transmit incident electromagnetic energy having wavelengths outside of the reflection band. The filter includes an antireflecting portion having a nominal refractive index profile selected to reflect a minimum amount of electromagnetic energy from a theoretical interface between a first medium having a first predetermined refractive index and a second medium having a second predetermined refractive index. A band rejecting portion has a periodic refractive index profile whose periodicity and amplitude are selected to reflect a maximum amount of electromagnetic energy within the relfection band. At least part of the nominal refractive index profile is modulated by the superposition thereon of at least part of the periodic refractive index profile. The entire periodic refractive index profile maybe superimposed on the monial refractive index profile, while the periodic refractive index profile may be a rugate profile. In addition, the nominal incident and substrate refractive index profiles may be quintic refractive index profiles.

Lattice‐parameter‐difference measurement of heteroepitaxial structures by means of extremely asymmetrical Bragg diffraction

Abstract: The sensitivity of measurements of the lattice-parameter difference in monocrystalline heterostructures can be enhanced by use of an extremely asymmetrical diffraction geometry. If the angle of incidence is somewhat higher than the critical angle for total external reflection, the Bragg peak is shifted from the position calculated by kinematic theory. The amount of shift depends on the angle of incidence as well as on the mass density of the material used. For heteroepitaxic structures both the layer and the substrate peaks are shifted but by different amounts. Therefore it becomes possible to characterize layers of totally lattice-matched structures also.

High efficiency reflectors and methods for making them

Abstract: An article of manufacture includes a substrate carrying at least two coating layers, one layer being of approximately quarter wave optical thickness, the other layer of approximately two quarter wave optical thickness, with the layers alternating between a material such as a dielectric having a first index of refraction and a second material such as a dielectric having a second index of refraction lower than the first index of refraction. These layers form a filtering system which removes narrow bands of light such as laser wavelengths by efficient reflection while permitting the remainder of the light spectrum to pass through the article. The coating layers have optical thicknesses and indices of refraction appropriate to reflect more than 99% of incident light at one or more predetermined wavelengths of light in the range of about 300 to about 1,200 nanometers and to transmit a substantial amount of all other incident light in the range. These articles are made by an electron beam evaporation technique under vacuum and under controlled conditions of temperature, partial pressure of oxygen, and deposition rates.

8. Adsorbed Monolayers and Intercalated Compounds

Abstract: Publisher Summary This chapter discusses that an enormous increase of research in the area known as “surface physics” or “two-dimensional physics,” and rapid growth in this area continues to this day This interest has been fueled partly by the technological importance of understanding the properties of surfaces and thin films, partly by some of the novel features of physics in dimensions less than three, and partly by the richness and variety of the phenomena available for study The most prevalent investigative tool for the study of surface structure has been low-energy electron diffraction (LEED) It also discusses that the biggest problem in such studies is to find ways to detect the weak diffraction signal from the surface and to prevent it from being overwhelmed by scattering from the bulk This may be accomplished in two ways; (1) to use materials that have very large specific surface areas and (2) to use the technique of total external reflection, that is, with the grazing angle that the incident radiation makes with the surface being less than the critical angle for total reflection The chapter discusses that neutron scattering has been a surprisingly successful probe for studying surface phenomena, particularly in physisorbed systems This has been due to the existence of graphite substrates with large and homogeneous surface areas that provide excellent model substrates with a low bulk signal in the regions of interest for the study of a variety of physisorption phenomena

An optical study of thin interfacial liquid films using total reflection of light

Abstract: The light totally reflected at the interface between a glass prism and a liquid (water) of lower index can be partly transmitted as a droplet of liquid of larger index (oil) approaches this interface. By using the variation of the reflected intensity, one can study the static structure and the thickness variation of the intermediate water film in a range of thickness of a few 10 A to 102 A. A preliminary experiment is presented together with the optical technique.

Wave reflection from inhomogeneous media at normal incidence

Abstract: Wave reflection from a medium with continuously varying refractive index is examined. A differential equation is developed, the solution of which yields the back-reflected part of a wave of unity amplitude incident on a non-homogeneous medium at normal incidence.

Wave reflection from inhomogeneous media at normal incidence

Abstract: Wave reflection from a medium with continuously varying refractive index is examined. A differential equation is developed, the solution of which yields the back-reflected part of a wave of unity amplitude incident on a non-homogeneous medium at normal incidence.

Reduced crosstalk optical switch

Abstract: An optical switch comprises a pair of glass prisms (10, 11) of refractive index n g and base angle θ one on either side of a liquid crystal interface (12) of positive dielectric anisotropy and having an extraordinary refraction index n o and an ordinary refraction index no. To reduce crosstalk the refractive index n g is so chosen that