Showing papers on "Total external reflection published in 2000"

Resonant magneto-optical properties of Fe near its 2p levels: [] Measurement and applications

Abstract: Resonant magneto-optical properties of Fe are considered across its $2p$ core levels. General equivalence of the classical magneto-optical formalism (dielectric tensor) and the resonant atomic scattering factor in the electric dipole approximation is shown in describing pure charge contributions as well as first- and second-order magnetic contributions. Thickness effects in transmission absorption measurements are considered and shown to be minimized in Faraday magneto-optical rotation measurements. Transmission absorption and Faraday rotation spectra obtained using linear polarization are normalized to the complex refractive index and atomic scattering factor for pure circular modes and their polarization average, showing that the pure magnetic part is roughly 50% of the pure charge part at the ${L}_{3}$ resonance. Magnetic linear dichroism (Voigt effect) measured in transmission is only 2% of the pure charge scattering at resonance. These magneto-optical constants are used to calculate important polarization-dependent experimental quantities including penetration depths, critical angles for total external reflection, Kerr rotation and intensity spectra, and interference and distorted-wave effects that modulate scattering intensities. The results reveal the importance of knowledge of these properties and use of full magneto-optical formalisms in planning and interpreting experiments involving resonant $2p$ optical properties of the $3d$ transition metals.

Refractive index of human whole blood with different types in the visible and near-infrared ranges

Abstract: Knowledge of the optical properties of human whole blood has always been of great interest for medical applications. The aim of this study was to provide the dispersive relations of refractive index of human whole blood with different types in the visible and near-infrared ranges and other conditions. In order to overcome the scattering effect, we applied an unusual method based on total internal reflection. A focused light, a semicylindrical lens in contact with tissues and a linear CCD camera are used in the experimental apparatus. The critical angle and therefore the refractive index can be obtained from the spacial distribution of internal reflective light. A monochromator is chosen as the light source, the chromatic dispersion curve of materials can be determined directly and quickly. A set of values has been presented that relates the refractive index to wavelength and types of whole, undiluted blood. Our results suggest that the refractive dispersions be almost the same in the visible and near-infrared ranges no matter which blood type it belongs to. In addition, the relationship can be described by Cauchy's formula.

Energy-dispersive, x-ray reflectivity density measurements of porous SiO2 xerogels

Abstract: X-ray reflectivity has been used to measure nondestructively the density of thin, porous, silica xerogels used for interlayer dielectric applications. The critical angle, defined through total external reflection, was measured for multiple x-ray energies to correct for sample misalignment error in the determination of the density for the films. This density was used to extrapolate the percentage porosity, assuming a bulk SiO2 density standard. The results were compared to those obtained by Rutherford backscattering and ellipsometry techniques.

Measurement of refractive-index change at a liquid-solid interface close to the critical angle.

Abstract: We measured the refractive-index change on a liquid sample, using the reflection of a polarized Gaussian laser beam close to the angle of total reflection. We applied this technique to a solution of nickel (ii) phthalocyanine tetrasulfonated (NiPTS) in water–ethanol (1/1 v/v), in which the nonlinearity of the refractive index is due to optically induced thermal effects. We show that close to the angle of total reflection the sensitivity of this technique is four times bigger than at normal incidence.

A parabolic mirror x-ray collimator

Abstract: A robust and stable x-ray collimator has been developed to produce a parallel beam of x-rays by total external reflection from a parabolic mirror. The width of the gold-coated silica mirror varies along its length, which allows it to be bent from a plane surface into a parabolic form by application of unequal bending forces at its ends. A family of parabolas of near constant focal length can be formed by changing the screw-applied bending force, thus allowing the collimator to cater for a range of wavelengths by the turning of a screw. Even with radiation with a wavelength as short as that as Mo K 1 ( = 0.07 nm), a gain in flux by a factor of 5.5 was achieved. The potential gain increases with wavelength, e.g. for Cu K 1 radiation this amounts to over a factor of ten.

On the use of total reflection x-ray topography for the observation of misfit dislocation strain at the surface of a Si/Ge–Si heterostructure

Abstract: Synchrotron x-ray topography was used in total reflection topography (TRT) mode to observe strain-induced surface bumps due to the presence of underlying misfit dislocations in strained-layer SiGe on Si epitaxial heterostructures. In these experiments, the x rays approached the sample surfaces at grazing incident angles below the critical angles for total external reflection for a number of reflections, and hence, surface strain features nominally less than a few tens of angstro/ms from the sample surface have been observed. These are similar to the surface bumpiness observed by atomic force microscopy, albeit on a much larger lateral length scale. The fact that TRT mode images were taken was confirmed by the observation of conventional backreflection topographic images of misfit dislocations in all samples when the grazing incidence angle became greater than the critical angle.

Folded cavity, broad area laser source

Abstract: A broad stripe semiconductor laser has a folded cavity that permits the laser to produce output powers into a high quality beam with low divergence. The folded cavity includes a first material region disposed within the cavity having a first refractive index and a second material region having a second refractive index less than the first refractive index, and forming a first interface with the first material region. The first interface is disposed to reflect a lowest order reflection mode light beam propagating within the first material region. The first interface is disposed at a predetermined angle so that the lowest order reflection mode intracavity light beam is incident on the first interface at an angle below the critical total internal reflection angle, and higher order reflection modes are incident on the first interface at angles in excess of the total internal reflection critical angle. The interface may be curved to control the divergence to the light emitted from the cavity.

Total reflection measuring apparatus

Abstract: PROBLEM TO BE SOLVED: To provide a total reflection measuring apparatus, capable of obtaining a total reflection by easily and accurately changing the incident angle using one apparatus. SOLUTION: The total reflection measuring apparatus 122 which obtains a totally reflected beam 120 converges an incident beam 118 at an incident angle of critical angle or larger to an abutting surface 131 of a total reflection prism with a sample to be measured. The apparatus 122 comprises an incident angle changing means 164, capable of changing the incident angle of the beam 118 to the surface 131 of a total reflection prism 110 with the sample 112 within a range of the angle capable of measuring total reflection. The apparatus 122 obtains the beam 120 by changing the incident angle of the beam 118 by the means 164.

Free-space thermo-optical devices

Abstract: A thermo-optical device to alter the direction and/or intensity of a light beam is described In the thermo-optical device, a first material in contact with a second material defines an interface therebetween The first and second materials have disparate thermo-optical coefficients such that, at a first temperature, the refractive indices of the two materials are the same and, at a second temperature, the refractive index of one material is less than the refractive index of the other material At the first temperature, when the two refractive indices are equal, a light beam incident on the interface is transmitted through the interface without refraction At the second temperature, the light beam propagating through one of the material, if incident on the interface at an appropriate angle, will be reflected off, instead of transmitted through, the interface

Stress relief mechanism for optical interference coatings

Abstract: An optical interference coating for reflecting infra-red radiation and transmitting visible light. The coating comprises alternating layers of high index of refraction material and low index of refraction material. As the total number of layers increases, the ratio of high index of refraction material to low index of refraction material must also increase.

Device for x-ray and fluorescent analysis

Abstract: X-ray spectrometric quantitative analysis of element composition of substance for X-ray and fluorescent analysis of microsamples SUBSTANCE: device for X-ray and fluorescent analysis incorporates source of primary X-ray radiation, mirror collimator in the form of wedge with reflecting internal surfaces, reflector in the form of logarithmic spiral, convex reflector in the form of transcendental curve, reflecting plate with sample mounted at angle of total external reflection with reference to formed beam and detector to raise sensitivity of it without increase of power of source thanks both to more complete concentration of radiation of formed beam on sample and to increase of input aperture EFFECT: raised sensitivity of device 1 dwg

The method of partial fluxes : Reflection of optical radiation from a semi-infinite homogeneous medium with a trinomial phase function

Abstract: This paper continues the analysis of the problem of light reflection from a semi-infinite dissipative medium. Using the method of flux separation, we perform an analytical calculation of the first partial reflection function S (1) integrated over the azimuthal angle in the case when the expansion of the scattering phase function in spherical harmonics involves three Legendre polynomials. The phase functions corresponding to isotropic and Rayleigh scattering of light from random scattering centers are particular cases of the phase function of the considered type. The first partial reflection function S (1) describes the angular distribution of photons that escape from the medium reversing the sign of their velocity projections on the direction of the inner normal only once. In the case of the normal incidence of radiation on the surface of a medium, the first partial reflection function is compared with the total reflection function S, obtained by the numerical solution of the relevant nonlinear integral equation. We analyze the influence of the parameters of the scattering phase function on the accuracy of the S (1) approximation. It is demonstrated that the first partial reflection function adequately describes even some specific features in the spectrum of reflected radiation, including local maxima and inflection points, For media with strong absorption, the quantities S and S (1 are shown to coincide with each other with an accuracy up to several percent. For media with weak absorption, the remaining part of reflected radiation (i.e., S- S (1) , which is associated with photons that reverse the sign of their velocity projections on the direction of the inner normal to the surface of the medium three and more times, is described by a dependence close to a cosine function.

II. Geometrical optics of variable-frequency light rays in special relativistic and nonrelativistic situations: The general law of reflection

Abstract: The general law of reflection concerns situations when the light ray undergoes a shift of frequency at the reflection point. For example, it governs reflection of light rays from a moving mirror (either in a vacuum or in a transparent medium), reflection from a motionless mirror coated with a layer of Raman-active molecules in the coherent-scattering regime, or external reflection of X-rays from the surface of a condensed matter sample, with partial dissipation of energy within the skin depth. The general law of reflection is derived from the extremum principle for propagation of variable-frequency light rays. It states that the angle of reflection depends not only on the angle of incidence but also on the frequency shift in the reflection point and dispersion of the refractive index of the medium in contact with the mirror. The compatibility of the general law of reflection and the special relativistic treatment of reflection is examined in detail. Applications of the new law of reflection are discussed ...

A method for the formation of ultrathin X-ray beams

Abstract: It is demonstrated that ultrathin beams with an effective cross sectionh≲100 nm and an angular divergence Δϕ≲2′ below the diffraction limit can be obtained. This is achieved by irradiating the edge of an optically polished face by an X-ray beam with a wavelength of ∼0.1 nm at a grazing angle close to the critical angle of total external reflection and subsequent transmission of the refracted beam through an adjacent side face. Under conditions ensuring effectiveh values of 81 and 96 nm, the values of Δϕ observed experimentally for GaAs and Si samples at wavelengths of 0.154 and 0.139 nm are much smaller than the diffraction limit calculated according to the theory of prism spectrometers. This allows for the formation of an X-ray probe that can be used for local analysis, for example, and layer-by-layer investigations of thin film structures.

Analysis of reflection coefficient dependence of fibre Bragg grating on index modulation profile

Abstract: We present the impact of changes in core refraction modulation profile and index on the shape of fibre Bragg grating reflection coefficient. It is shown that there exists a shift of reflection coefficient characteristics towards longer wavelengths and an increase in amplitude and the grating effective length as well. Reflection coefficient shapes are plotted for the profile described by hyperbolic tangent function for the selected positive values of a parameter.

Light Amplification and Attenuation in Stratified Structures with Complex Refractive Index

Abstract: We report a new kind of laser threshold resonance in electromagnetic wave propagation inside a layered medium. Specifically, for large values of the gain coefficient, the wave interaction with only the first few lattice interfaces results in transmission and reflection values much greater than unity. We also show that the duality phenomenon between losses and gains on the field amplitude decay is due to the existence of counter-propagating waves on reflection from the layer interfaces.