Showing papers on "Total internal reflection published in 1987"

Optical coherence-domain reflectometry: a new optical evaluation technique.

Abstract: An optical evaluation technique is described that is suitable for determining the positions and magnitudes of reflection sites within miniature optical assemblies. This method utilizes the coherence effects exhibited by a broadband optical source and is referred to as optical coherence-domain reflectometry. Background theory is given, and experimental results have demonstrated a resolution of 10 μm with an optical dynamic range of more than 100 dB.

New Green-function formalism for surface optics

Abstract: A new Green-function formalism is developed for calculating fields generated by sources in the presence of a multilayer geometry. The approach is to formulate the problem immediately in terms of s- and p-polarized waves generated, so that the calculation of the effect of interfaces proceeds by the introduction of Fresnel reflection and transmission coefficients and parallels the simple physical picture of light progressing through the structure.

Fluorescence emission at dielectric and metal-film interfaces

Abstract: It is well known that the classical optical properties of a bare or metal-film-coated dielectric surface significantly the emission pattern of a fluorophore in close proximity to it. Most previous classical calculations of this perturb model the fluorophore as a continuous fixed-amplitude dipole acting as a simple radiator. However, for effect modeling steady-state excitation, a fixed-power dipole is more appropriate. This modification corresponds to normalizing fixed-amplitude dipole intensities by the total dissipated power, which is itself dependent on fluorophore orientation and proximity to the surface. The results for the fixed-power model differ nontrivially from the fixed-amplitude model. Using the fixed-power dipole model, we calculate the observation-angle-dependent intensity as a function of the fluorophore’s orientation and distance from the surface. The surface can have an intermediate layer of arbitrary thickness on it, which is used to model a metal-film-coated dielectric. In addition, general expressions are derived for the emission power as observed through a circular-aperture collection system (such as a microscope objective) located on either side of the interface. These expressions are applied to several common cases of fluorophore spatial and orientational distributions at bare glass–water and metal-film-coated glass-water interfaces. The results suggest practical experimental approaches for measuring the spatial and orientational distribution of fluorophores adsorbed at a surface, utilizing the distance-dependent fluorescence near a metalized surface and optimizing the collection efficiency from a well-defined volume near a quenching surface.

Dielectric totally internally reflecting concentrators

Abstract: Dielectric totally internally reflecting concentrators (DTIRCs) which can achieve concentrations close to the thermodynamically allowed limits are introduced. General design methodologies are given explicitly. Geometrical and optical properties of DTIRCs are discussed.

Grazing incidence synchrotron x-ray diffraction method for analyzing thin films

Abstract: A method using synchrotron radiation parallel beam x-ray optics with a small incidence angle α on the specimen and 2Θ-detector scanning is described for depth profiling analysis of thin films. The instrumentation is the same as used for Θ:2Θ synchrotron parallel beam powder diffractometry, except that the specimen is uncoupled from the detector. There is no profile distortion. Below the critical angle for total reflection αc, the top tens of Angstroms are sampled. Depth profiling is controlled to a few Angstroms using a small α and 0.005° steps. The penetration depth increases to several hundred Angstroms as α approaches αc. Above αc there is a rapid increase in penetration depth to a thousand Angstroms or more and the profiling cannot be sensitively controlled. At grazing incidence the peaks are shifted several tenths of a degree by the x-ray refraction and an experimental procedure for calculating the shifts is described. The method is illustrated with an analysis of iron oxide films.

Solar concentrator and manufacturing method therefor

Abstract: A solar concentrator comprises a prism having radiation input, reflection and output faces. Located on the input and/or reflection face(s) is a layer of material with a formed three-dimensional hologram of transmitting type in the case of the input face or of reflecting type in the case of the reflection face. The structure of the hologram permits radiation input to the prism at an angle greater than the critical angle of total internal reflection to be reflected within the prism without being diffracted by the hologram.

General electromagnetic theory of total internal reflection fluorescence: the quantitative basis for mapping cell-substratum topography.

Abstract: Total internal reflection fluorescence (TIRF) has recently been used to look at the contacts made between cells and a glass surface on which they are spread. Our method utilizes the fluorescence of a water-soluble dye that acts as an extracellular aqueous volume marker. Fluorescence is stimulated by the short-range electric field near the glass surface that exists under conditions of total internal reflection. Since fluorescence is normally generated beneath a spread cell and not beyond it, the fluorescence of the image is related to the size of the cell-glass water gap. The images obtained are remarkable for their detail, contrast and the absence of confusing granularity due to cytoplasmic heterogeneity, which is commonly seen in interference reflection (IRM) images. We here develop a rigorous electromagnetic theory of total internal reflection in layered structures appropriate for cell contacts and apply it to quantitative TIRF. We show that: (1) TIRF, unlike IRM, can report cell-glass gaps in a way that is practically independent of the detailed physical properties of the cell; (2) TIRF is also far more sensitive than IRM for measuring cell-glass water gaps up to approximately equal to 100nm. These striking results explain the image quality seen by TIRF. As the initial step towards verifying our theory we show that measurement of the fluorescence stimulated by total internal reflection at a simple glass-water interface matches theoretical predictions.

Röntgenkleinwinkelbrechung an Metalldrähten, Glasfäden und hartelastischem Polyproplen

Abstract: Very thin equatorial small-angle scattering of Cu Kα radiation is observed from metallic wires, glass fibres and hard elastic polypropylene which can be explained quantitatively as a refraction phenomenon if the excess refractive indices n = 1 - ∊ of the samples are smaller than unity. For Cu Kα radiation and SiO2 glass ∊ has a value of 7.2 × 10-6. The intensity Is of reflection within a total reflection angle δ = 3.8 × 10-3 = 13' is negligibly small compared with the intensity of refraction IB. In addition to refraction, diffraction by gaps and holes in strained polypropylene was observed. The scattering of 60 μm particles of Li-Ba silicate glass powders [Nau & Bruckner (1971). Kolloid Z. Z. Polym. 244, 223-233] can be explained by transforming the observed scattering of spheres to cylinders yielding the refraction IB as calculated.

Evanescent detection of adsorbed protein concentration-distance profiles: fit of simple models to variable-angle total internal reflection fluorescence data

Abstract: Total internal reflection fluorescence spectroscopy (TIRF) is an established technique for following the course of interfacial reactions. Theoretically, by gathering TIRF data as a function of observation angle, one can obtain the density of fluorophores with respect to distance away from a solid/liquid interface. In order that the practical application of the theory might be explored, variable observation angle data from solutions of fluorescein and from adsorbed layers of fluorescein isothiocyanate labeled immunoglobulin have been analyzed in terms of simple concentration-distance profiles. In all cases the general shape of the data curves was found to conform to the theoretical expectation. Layer thickness determinations varied over a range of 20 to 100 nm, with concentrations in the layer ranging from 12 to 61 mg/mL. The theoretical background, sources of error, and system improvements are also discussed.

Finger imaging apparatus using curved platen

Abstract: A curved cylindrical segment platen has a concave touching surface. An interrogating slit light beam is scanned around the platen to scan a finger held against the touching surface. An optical imaging system images the zone illuminated onto an array of photo-transducers to provide a signal representing the fingerprint. The optical system is rotated around the platen. The axis of the interrogating light beam is substantially normal to the touching surface. The axis of the imaging system is off normal by about 56 degrees, an amount which is greater than a critical angle equal to the maximum angle of refraction in the platen. This critical angle is approximately 41 degrees. The axis of the imaging system is also off normal to the non-touching surface by an angle that is less than this critical angle of 41 degrees and thus less than the angle of total internal reflection. As a consequence, the image at the photo-transducers provides a completely dark valley zone and a sharply contrasting light image ridge zone. In a second embodiment, a thick flat platen has a flat touching surface and an opposed parallel flat surface through which an illuminating light beam is applied to scan across a finger applied to the touching surface. The illuminating beam is normal to the touching surface. The axis of the imaging system is at an angle of approximately 50 degrees to the normal, an angle that is thus well past 41 degrees, the maximum angle of refraction. The platen has a side face which is at an angle of 45 degrees to the touching surface. The imaging axis emerges from this sloping side face at an angle to the normal that is substantially less than the angle of total internal reflection.

Method of making travelling wave semi-conductor laser

Abstract: A triangular ring laser utilizing total internal reflection at two angled facets and a preselected amount of reflection at a third angled facet is disclosed. Partial transmission occurs through the third facet to reduce the threshold current required for achieving stimulated emission. The facets are at three corners of the triangular laser, and are formed by chemically assisted ion beam etching in which SiO 2 is used as a mask, whereby smooth vertical walls are produced to form facets having reflective characteristics equivalent to those formed by cleaving.

Photo semiconductor device having a multi-quantum well structure

Abstract: A multi-quantum well structure which is formed by laminating thin semiconductor layers is provided with means for injecting carriers in a direction which is parallel to the surface of the laminated thin semiconductor layers, whereby it is possible to obtain satisfactory changes in refractive index of the carrier injection portion. For example, if the total reflection region of an optical switch consisting of optical waveguides which cross each other is provided with a multi-quantum well structure wherein carriers are injected in a direction parallel to the surface of the well, the extinction ratio characteristics of the device can be improved.

Sensor for mixing ratio of gasoline and alcohol

Abstract: A sensor for mixing ratio of gasoline and alcohol comprising: a transparent column, both ends of which are supported by grips; the surface of the column is positioned in direct contact with a mixing liquid of gasoline and alcohol; a light emitting diode disposed so that light beams therefrom are incident on one end of said transparent column and the mixing liquid, said beams incident on said boundary at less than a critical angle being totally refracted, while said beams incident on said boundary at more than the critical angle being totally reflected to pass within said column so as to go out from the other end thereof, said critical angle depending upon a mixing degree of said liquid; a photo diode placed to receive the light beams reflected from the boundary so as to generate an output in accordance with the quantity of the light beams received; and the column being substantially determined its lengthwise and diametrical dimension such that the light beams incident upon the boundary at a critical angle, are allowed to totally reflect only once to enter the photo diode with the mixing ratio of alcohol and gasoline ranging from 100:0 to 0:100.

Measurement of Ultrasonic Wavespeeds in Off-Axis Directions of Composite Materials

Abstract: The relationship of NDE with structural analysis is to provide quantitative information about material mechanical properties. For a composite structure (such as a rocket motor case) which is designed to handle in-plane loading, NDE should, ideally, provide information about the in-plane stiffness and strength properties of the structural material [1]. Because acoustic wave propagation depends on material elastic properties as well as being sensitive to material inhomogeneities, ultrasonic NDE has been nominated as a viable means of satisfying the needs of structural analytical modeling [2]. To address the need to detect in-plane properties, leaky Lamb wave [3,4] and non-normal incidence transmission [1] methods are being developed, for example. Development of composite ultrasonic NDE techniques, which are sensitive to material mechanical properties in the plane of a structure, required an understanding of acoustic wave propagation in anisotropic media. If a wave is introduced into the structure wall with an oblique angle of incidence less than critical angle, the refracted wave will travel in a non-principal or off-axis direction of the composite material. As a result, the wave energy will not generally travel in a direction normal to its phase fronts as it would in an isotropic medium. The acoustic wave energy or wave group propagates at a deviation angle, ψ, with respect to the phase front normal [5,6] as shown in Fig. 1. The deviation angle should be considered when measuring acoustic phase velocities from which the stiffnesses are calculated. The following sections discuss the effect of the group velocity propagation direction upon phase velocity measurements of quasi-longitudinal and quasi-shear waves propagating in non-principal directions in principal planes of orthotropic composite materials. Experimental results are shown for unidirectional graphite composite material samples.

Nanosampling via internal reflection spectroscopy

Abstract: Internal reflection spectroscopy has a number of advantages over other spectroscopic techniques. It can be used with liquid or solid samples, and little or no sample preparation is required. Since it is necessary only to bring the sample in contact with the sampling surface of an internal reflection element (IRE), sample handling is much simpler than it is for other techniques. This is especially important for very small samples (e.g., microgram and nanogram quantities), for which there is currently very wide interest. Furthermore, it has been shown that the interaction of the light (electromagnetic wave), under the right conditions, is stronger for internal reflection than it is for transmission or external specular reflection. Therefore, because of the above-mentioned advantages, internal reflection is the preferred method of micro- and nanosampling.

Optical effects of surface plasma waves with damping in metallic thin films.

Abstract: Effects of optical absorption on surface plasma waves are computed from the Fresnel reflection and transmission coefficients for a metallic thin film. It is shown that the angle of incidence at which the reflectivity exhibits a deep minimum is greater than the angle of incidence at which the H field of the surface plasma wave at the metal–vacuum surface exhibits maximum amplitude. Surface plasma waves can have maximum amplitude at an angle of incidence where reflectivity is near maximum, and a deep minimum in reflectivity can occur without the simultaneous excitation of intense surface plasma waves.

Polarization and Brewster angle properties of light pillars

Abstract: Numerical simulation of the nocturnal light pillar, an atmospheric optical phenomenon inadvertently caused by humans, reveals that the pillars are virtually completely polarized at the Brewster angle for ice as a result of the geometry of rays reflected off near-horizontally aligned ice crystals from a nearby light source. It is also shown for plate crystals that the first-order internal reflection contributes importantly to the display and that the depth of the crystal-containing layer and the effects of atmospheric attenuation serve to limit the height above the horizon to which the pillars are visible. The model findings have been verified with experiments involving the generation of artificial pillars from linearly polarized light sources. Both observations and model predictions support the view that the plate ice crystals causing the display have tilt angles that are distributed normally from the horizontal plane.

Approximate solution of eigenmode problems for layered coupled waveguide arrays

Abstract: The characteristic modes of coupled waveguide arrays with a simple layered structure are examined using the approximate coupled wave theory. It is shown that evanescent waves may arise from total internal reflection at a boundary between two semi-infinite arrays. The transmission and reflection coefficients for this process are derived. If a suitable, finite, array is sandwiched between two semi-infinite arrays so that total internal reflection occurs at both boundaries, "guided" characteristic modes may arise. These have most of their power confined between the boundaries. The theory is used to specify an array distribution suitable for use in a transverse-mode-locked array laser.

Traveling wave semi-conductor laser

Abstract: A triangular ring laser utilizing total internal reflection at two angled facets and a preselected amount of reflection at a third angled facet is disclosed. Partial transmission occurs through the third facet to reduce the threshold current required for achieving stimulated emission. The facets are at three corners of the triangular laser, and are formed by chemically assisted ion beam etching in which SiO2 is used as a mask, whereby smooth vertical walls are produced to form facets having reflective characteristics equivalent to those formed by cleaving.

Parasitic Oscillations And Amplified Spontaneous Emission In Face-Pumped Total Internal Reflection Lasers

Abstract: Parasitic oscillations and amplified spontaneous emission (ASE) can often strongly influence the operation and efficiency of laser devices, as has been shown previously for disk and active-mirror amplifiers. Here we report the first comprehensive investigation of those phenomena in total internal reflection (TIR) face-pumped lasers. The results to be presented here were made possible by the development of two three-dimensional computer codes. The first (PARA) systematically searches for parasitic oscillations in slab lasers and determines the gain required to reach threshold. Our second code (AMSPE) is a three dimensional raytrace model which includes temporal gain and allows for non-uniform gain profiles. AMSPE calculates the gain depletion as well as changes in spatial gain profile and thus the decrease in amplifier efficiency as a function of a number of critical parameters such as slab aspect ratio, spontaneous emission spectral profile, and slab face angle. In this paper we first review the classes of parasitics in slab lasers and show how symmetry breaking can significantly increase the energy storage capability of such deyices. We then review the construction of the AMSPE code and show how it may be used to identify maximum efficiency slab laser configurations.

Prism couplers in guided-wave optics: design considerations.

Abstract: Two important considerations for designing coupling prisms for optical waveguides are (a) coupling the incident wave to the full range of effective indices for the modes in the waveguide and (b) the ability to observe the optically contacted area, the wet spot, between the prism and waveguide. The latter becomes a problem with high-index prisms owing to total internal reflections. Design parameters for prisms satisfying both of these requirements are derived, and numerical examples are presented for both symmetrical and right-angle rutile prisms.

Method and apparatus for determining the level of an analyte in a sample of whole blood

Abstract: A method for determining the level of an analyte in a sample of whole blood uses the technique of internal reflection spectroscopy and an apparatus suitable for the technique. The method is of particular use to detect the attenuation of the totally reflected light by absorption of the evanescent wave, e.g., by haemoglobins. In the apparatus (1) incident light is directed via a light guide (7) to the reflection element (3) and the attenuated totally reflected light is directed out of the element to a photodetector (12) by a light guide (11). In the whole blood in the cuvette (18) the cells are removed from the interface (8) by gravity to leave blood cell free plasma (4) adjacent the interface (8). Thus analytes present in the plasma can be detected. The extent of haemolysis can be estimated.

Use of a Conical Axicon as a Surface Acoustic Wave Focusing Device

Abstract: Ultrasonic axicons generate waves which focus on a line. They are used in various imaging applications as hulk wave focusing devices with a very long depth of focus. A new type of conical axicon is introduced. It consists of a concave parabolic surface immersed in a liquid medium and insonified obliquely by wavefronts generated by a plane transducer. The parabolic cylinder can be approximated by a portion of a circular cylinder without losing significantly in the focus- ing performance of the axicon. It is also shown that conical axicons can be used to excite surface waves provided that the cone angle of the axicon coincides with the Rayleigh critical angle of the liquid-solid in- terface. The generated surface waves focus into a diffraction-limited spot. This new surface wave focusing scheme is easy to use and has a conversion efficiency and sensitivity far better than other existing tech- niques.

What can the polarisation of shear waves tell us

Abstract: The direction of polarisation of seismic shear waves and the time shift between shear-wave arrivals of different polarisation contain important clues to the internal structure of the medium through which the waves have passed. For instance, the direction of polarisation can be used to infer the average orientation of cracks (and thus the direction of tectonic stresses), while the time shift depends not only on the orientation of the ray path with respect to the plane of the cracks, but also on the product of crack density and path length through the cracked medium. Before the direction of polarisation and the time shift can be used for this purpose, one must ascertain that these parameters are not contaminated by spurious effects. Disturbances that must be corrected for occur at the free surface, but even in vertical seismic profiles (VSPs) disturbances might occur due to transmission through interfaces: unless the shear waves are polarised parallel or perpendicular to the 'plane of propagation' that contains the ray and the normal to the interface (or unless the angle of incidence is zero), the direction of polarisation changes at transmission due to the different transmission coefficients of the two component waves. For incidence at and beyond the critical angle, the transmission coefficient of the component parallel to the plane of propagation is complex, resulting in a time shift. The effects at the free surface and at individual interfaces are relatively small (though not negligible). However, passage through several interfaces can lead to the accumulation of time shifts. In the limit this accumulation results in two shear waves with different veloeities, i.e. to anisotropy.

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.

Focal shift of convergent ultrasonic beams reflected from a liquid-solid interface

Abstract: It is shown by schlieren photography that a convergent acoustic beam reflected from a liquid–solid interface can exhibit a focal shift in the axial direction when the angle of incidence deviates slightly from the critical angle. The results confirm the recent predictions of Bertoni et al. [Trait. Sign. 2, 201–205 (1985)] about this interesting detail of the general Rayleigh angle phenomenon.

Reflection and transmission of ultrasound from a planar interface

Abstract: Information about the local forces at an interface between two solids is of considerable technological interest. We have used a simple model of a homogeneous solid. We consider a cubic crystal with springs connecting the nearest and the next nearest neighbors. Two such crystals can be joined by a different set of springs at the interface. The force constants of the springs at the interface describe the local forces at the interface. If a longitudinal wave is incident on such an interface at an angle less than the critical angle, it will be partly reflected and transmitted as a longitudinal and transverse wave. We have derived the equations for the transmitted and reflected amplitudes. These can be expressed in terms of the macroscopic properties of solids on either side of the interface, and in terms of the force constants at the interface. It is shown that at low frequencies our equations reduce to those derived from macroscopic theory in which it is assumed that the bond at the interface is perfect and that the boundary atoms on both sides of the interface have equal displacements. If the force constants at the interface are weak compared with the force constants in the bulk media on either side of the interface, deviations from the macroscopic results occur. Thus, measurements of scattered wave amplitudes at frequencies where the deviation from macroscopic results occurs can provide valuable information about the nature of forces at the interface.