Showing papers on "Total internal reflection published in 1989"

Sensitivity of grating couplers as integrated-optical chemical sensors

Abstract: Grating couplers on planar waveguides can be used as integrated-optical sensors responding to (1) changes in the refractive index of a liquid sample covering the waveguide (differential refractometer) and (2) the adsorption and desorption, respectively, of molecules out of a gaseous or liquid sample on the waveguide (gas or chemical sensor). A theory of the sensor sensitivities is developed; conditions for the waveguide parameters in order to obtain high sensitivities are derived. It is shown that effects (1) and (2) can be distinguished by measurements of the effective index changes of both the TE0 and the TM0 modes. In the analysis both nonporous and microporous waveguiding films are considered.

Refractive index of some mammalian tissues using a fiber optic cladding method.

Abstract: The index of refraction n of the many mammalian tissues is an important but somewhat neglected optical constant. Archival and oral papers have quoted the use of values of n for tissue generally ranging from 1.35 to 1.55. However, these values are frequently without experimental basis. They have arbitrarily used values near that of water, which is a major component of mammalian tissue, or have calculated a theoretical n from the weighted elemental composition of tissue. Since these values have not been precise and little information is available on specific indices for each tissue, a study was undertaken to develop a simple, rapid, and reliable method for the experimental determination of n. This was done using the ubiquitous quartz optical fiber. By substituting the usual cladding found on commercial quartz optics by the tissue in question and utilizing the principle of internal reflection, the value of n for the specific tissue can be calculated. This is done by utilizing the known indices for air and quartz and measuring the angle of the emergent cone of light from the output of the optical fiber. A number of indices for mammalian tissue (bovine, porcine, canine, and human) have been determined at 632.8 nm. With few exceptions, for tissues at this wavelength, n was in the 1.38-1.41 range. The species type did not appear to be a factor. Bovine muscle showed normal dispersion characteristics through the visible wavelengths. The denaturation of tissue was shown to alter significantly the refractive index.

New form of scanning optical microscopy.

Abstract: The exponential decay of the evanescent field due to the total internal reflection (TIR) of a light beam in a prism is used to advantage in a new form of scanning optical microscope, the photon scanning tunneling microscope (PSTM). The PSTM is the photon analogue of the electron scanning tunneling microscope. The sample is placed on or forms the TIR surface and spatially modulates the evanescent field. Changes in intensity are monitored by a probe tip scanned over the surface, and the data are processed to generate an image of the sample. Subwavelength resolution in three dimensions is obtained because of the exponential nature of the evanescent field intensity. Images produced by a prototype instrument using 633-nm light and a 1-\ensuremath{\mu}m probe tip are shown to have a lateral resolution of about 200 nm.

Total internal reflection fluorescence microscopy.

Abstract: Total internal reflection fluorescence (TIRF) microscopy provides a means to selectively excite fluorophores in an aqueous or cellular environment that is very near a solid surface (within ≤100 nm: less than one-fifth the thickness of a confocal microscopy section) without exciting fluorescence from regions further from the surface. Fluorescence excitation by this thin zone of electromagnetic energy (called an evanescent field) results in images with very low background fluorescence, virtually no out-of-focus fluorescence, and minimal exposure of cells to light in any other planes in the sample. Figure 21-1 shows an example of TIRF on intact living cells in a culture compared with standard epifluorescence. The above features have led to numerous applications, including the following:

Surface plasmon resonance sensors

Abstract: A surface plasmon resonance (SPR) sensor is adapted for biochemical and similar testing on large area samples such as the gel of an electrophoresis apparatus. The gel is sandwiched between a pair of plates. One of the plates is of transparent material and, sandwiched between itself and the gel is a metal layer of a mosaic of silver dots. Light from a source is directed via a reflector and undergoes total internal reflection at the interfacce between the transparent plate and metal layer. The reflected light is passed via another reflector to a light detector. The equipment is arranged so that SPR occurs at the metal layer, which resonance is critically dependent upon the refractive index of the gel. The structure including the light source and detector, together with reflectors is caused to scan across the gel surface to enable a two-dimensional representation of the changes in refractive index across the gel to be built up. This enables the progress of sequencing to be monitored.

Time domain reflection methods for dielectric measurements to 10 GHz

Abstract: Total reflection methods and instrumentation for their use are described for measurements of dielectric permittivity and loss at frequencies to 10 GHz or more. Several cell designs are shown, together with analyses of their performance. Procedures are given for correcting effects of wave propagation in the cells and residual reflections in the cells by bilinear analysis with calibrations using dielectrics of known permittivity. Representative results are presented for highly polar liquids, dilute solutions of polar molecules in nonpolar solvents, electrolyte solutions, and ionic glasses with appreciable ohmic conduction.

Optical biosensor system

Abstract: An optical biosensor system using internal reflection versus angle of incidence determination for the detection of biomolecules, said system comprising a sensor unit (10) with at least two sensing surfaces (39A-D), a source of light (1), and lens means (2) for forming a convergent beam of light which is focused in wedge-shape fashion to form a streak of light (5) extending transversely over all the sensing surfaces; a photodetector device (7) in the form of a two-dimensional matrix of individual photodetector; optical imaging instrumentation in the form of an anamorphic lens system (6) for the purpose of imaging rays of reflected light from the sensing surfaces on each its own column of photodetectors, so that for each sensing surface there is a corresponding set of columns of photodetectors; and an evaluation unit (8) for determining the minimum reflectance or the resonance angle at each of the sensing surfaces. The invention also relates to a method for calibrating the biosensor system, a method for correcting for baseline drift as well as a method for temperature regulation of thermostat means in the biosensor system.

Frequency-selective reflection and transmission by a periodic dielectric layer

Abstract: The feasibility of using a periodic dielectric layer, composed of alternating bars having dielectric constants epsilon /sub 1/ and epsilon /sub 2/, as a dichroic surface at millimeter-wave frequencies is examined For oblique incidence, it is found that total transmission and total reflection can be obtained at different frequencies for proper choices of epsilon /sub 1/ and epsilon /sub 2/ and the geometric parameters The frequencies of total reflection and transmission can be estimated from wave phenomena occurring in a layer of uniform dielectric constant equal to the average value in the periodic layers For some of the frequencies of total transmission, the bandwidth for 90% transmission is found to be 40% The bandwidth for 90% reflection is always found to be much narrower, the greatest value obtained being 25% >

The scattering of x rays from nonideal multilayer structures

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.

X-ray standing waves at a reflecting mirror surface.

Abstract: Generation d'ondes RX stationnaires au-dessus d'une surface de miroir d'or durant la reflexion externe totale

Infrared reflection spectroscopy of the SiO2‐silicon interface

Abstract: An infrared reflection technique, devised to study the structure of very thin films on substrates of high refractive index, yields an optical spectrum amplification of three orders of magnitude. With the aid of an infrared polarizer, an unanticipated peak at 1240 cm−1 in the internal reflection spectrum of thin (5–100 A) thermal SiO2 films on silicon has been identified as a longitudinal optical phonon peak. The unambiguous identification of this peak supports a similar interpretation of the 1230‐cm−1 peak in oxygen‐containing silicon first proposed by Hu in 1980.

Optical heterodyne sensor using the Goos-Hänchen shift.

Abstract: A new sensing scheme, capable of measuring various quantities using the Goos–Hanchen shift in the polarization phase domain, is proposed. The phase retardation between s and p polarizations on total reflection is enhanced by using multiple reflections in a plane-parallel transparent plate. This phase shift can be sensitively and stably detected using an in-line heterodyne method. As an application of this method, a displacement sensor utilizing the deflection of a light beam by a lens is developed. This displacement sensor has a resolution of 60 nm over a dynamic range of 120 μm. Good agreement between theoretical and experimental results is shown.

Scattered total internal reflectance immunoassay system

Abstract: A new immunoassay system is provided for the detection of ligands or ligand binding partners in solution in a heterogeneous format. The invention relies upon the detection of back scattered light from an evanescent wave disturbed by the presence of a colloidal gold label brought to the interface by an immunological reaction. The evanescent wave existing at the interface in turn is the result of a totally internally reflected incident light wave. Placement of the detector at a back angle above the critical angle insures a superior signal-to-noise ratio.

Diffraction of SV waves by circular canyons of various depths

Abstract: The scattering and diffraction of plane SV waves by circular cylindrical canyons of various depths in an elastic half space is studied in this paper. The canyons studied here range from shallow circular to semicircular canyons in an elastic half-space. The series of Bessel function expansions is used to solve the problem. For incidence beyond critical angle, the surface waves generated are expanded in terms of finite Fourier series that also involve Bessel functions. The number of steps and operations involved in the calculations is small and the method is applicable to a wide range of frequencies, thus making it preferable to the presently available numerical techniques. The surface displacement amplitudes and phases that are presented shows that the results depend on the following parameters; (1) The angle of incidence, θ\Gβ\N; (2) the ratio of canyon depth to its half width, \Ih\N/\Ia\N; (3) the dimensionless frequency of the incident SV wave, \Ighn; and (4) Poisson’s ratio, \Nν\N. The presence of the canyon in the elastic half space results in significance deviation of both the displacement amplitudes and phases on nearby ground surface from that of uniform half space motions, especially at high frequencies.

Polymeric optical waveguide switch using the thermooptic effect

Abstract: An all-polymeric optical waveguide switch which uses total internal reflection from a thermally induced index barrier is discussed. Very large effective index changes Delta N=2*10/sup -2/ were found in the polymeric waveguide. The temperature under the evaporated stripe heater was measured from the change in its resistance. The effective index change due to the temperature increase agrees well with values calculated from the deflection angles. The operation of the switch is, apart from a small waveguide dispersion effect, polarization-insensitive. Switching times of about 10 ms were measured. It should be possible to reduce them to a few milliseconds in optimized thermal designs and with regulated power dissipation in the heater. >

Light and temperature distribution in laser irradiated tissue: the influence of anisotropic scattering and refractive index.

Abstract: The rigorous method of discrete ordinates was used to evaluate the effects of anisotropic scattering and optical discontinuity at the boundaries on light and temperature distribution in tissue. The influence of optical parameters of tissue on its thermal response was examined by using a finite element solution of the heat conduction equation. Calculations were performed for wide ranges of scattering albedo, the anisotropy factor, as well as interface reflectivities. This study shows that the presence of an optical discontinuity due to an air–tissue interface forces the maximum peak intensity to move from subsurface to the surface for tissue with high scattering albedo, which leads to a higher fluence rate in the near surface region. Temperature field calculations show a higher subsurface temperature for a highly scattering medium during tissue coagulation. Neglecting the anisotropic properties of tissue as well as the optical discontinuity at the boundaries would result in considerable error in the calculated temperature rises. Additionally the accuracy of the photon diffusion theory for predicting light and temperature distribution near the tissue surface is examined.

Pulsed photothermal radiometry in turbid media: internal reflection of backscattered radiation strongly influences optical dosimetry

Abstract: The integrated irradiance (energy fluence rate) within tissue can exceed the incident irradiance due to backscattered and multiply reflected light near the sample surface. This was studied quantitatively using pulsed photothermal radiometry, which measures blackbody radiation emitted by a sample during and after absorption of an optical pulse. Aqueous gels containing absorbing dye with or without various scattering materials were studied using a fast sensitive IR detector system and 1-μs tunable pulsed dye laser. For nonscattering samples, the temperature transient (T-jump) due to absorption of a laser pulse was consistent with Beer’s law for homogeneous absorbing media. When scattering was present, increases of up to almost an order of magnitude in the T-jump were observed. For a given absorption coefficient, there was a proportional relationship between the increase in the T-jump and the sample’s diffuse reflectance. A model describing the reflectance of diffuse radiation at the sample boundary was derived to explain this result. To test the model, the refractive index was varied with air as the external medium and was also matched to that of BaF2 as the externalmedium. The subsurface fluence is, to a reasonable approximation, given by E ≅ E0(1 + 2bR), where E0 is the incident fluence of an infinitely wide collimated beam, b is a coefficient strongly dependent on only the refractive index, and R is the measured diffuse reflectance of the sample. This study shows that irradiance within tissues can greatly exceed the irradiance of incident collimated light, an effect that should be accounted for in photomedical dosimetry or research.

Method and apparatus for analyzing material properties using reflected ultrasound

Abstract: A method and apparatus which assesses the mechanical properties of a material by launching an ultrasound signal at the material while varying the angle of incidence and analyzing the amplitude of the ultrasound wave reflected by the material. The method and apparatus correlates extrema (maxima or minima inflection points) in the reflected angle with the angle of incidence of the transmitted signal to identify critical angles of incidence. The velocity of the pressure wave in the material has been found to be a function of a first critical angle corresponding to a first maxima as the angle of incidence is increased in the range 0°-90°. The velocity of the shear wave in the material has been found to be a function of a second critical angle corresponding to a second maxima following the first maxima. Young's modulus of elasticity, Poissons's modulus, and density can be approximated using the velocity of the pressure wave and shear wave for isotropic materials. A third critical angle corresponding to a minima after the first critical angle (reflected amplitude approaching 0) has been found particularly useful in conjunction with the first and second critical angles in assessing bone density and in determining whether the second critical point is at a maximum or an inflection point. The extension of the method in which the plane of scattering is rotated around the normal to bone while keeping the point of observation fixed has been found particularly useful in assessing the mechanical properties of anisotropic materials such as cortical bone.

Liquid crystal optical switching device

Abstract: A pair of transparent trapezoidal prisms each having angled endfaces with the larger bases in juxtaposition with respect to each other forming an interface therebetween are provided with at least one optical input and output coupled to the angled endfaces of the prisms. Optical radiation is applied to the input and normal to the angled endface at an angle greater than the critical angle with respect to the interface between the prisms. A liquid crystal beam splitter is positioned in the interface for splitting the radiation between the prisms each of which has a liquid crystal optical shutter positioned in the respective prisms to receive optical radiation which has been transmitted or reflected from the beam splitter at an angle normal to the optical shutter. Each of the shutters is provided with a variable biasing voltage of a continuous nature which is selectively variable for controlling the radiation passing therethrough thereby forming a controllable optical switch.

Fiber optic continuous liquid level sensor

Abstract: A fibre optic sensor, particularly for ascertaining fluid levels, utilizes two cylindrical lightguides with regular perturbations to emit and/or accept light in a radial direction. Each waveguide is coupled to one (or more) light source and/or to one (or more) light detector. A light source such as a light emitting diode or laser diode is coupled to the lightguide which emits radially, illuminating a planar dielectric surface, which in the presence of a fluid with a low index of refraction, e.g. air, behaves as a mirror, coupling light via total internal reflection to the lightguide which accepts this light radially and channels the light to a light detector. In the presence of a fluid with a high index of refraction, for example water, at the planar dielectric surface the fluid dielectric interface becomes primarily transmissive, with relatively little light being coupled to the lightguide which accepts light radially. The optical signal received at the light detector is thus related to the depth of the planar dielectric surface which is immersed in liquid. Several different embodiments to achieve liquid level sensing, as well as a scheme for eliminating sensitivity to optical signal changes induced in the lead fibre, are disclosed.

Cuvette for receiving liquid sample

Abstract: A new immunoassay system is provided for the detection of ligands or ligand binding partners in solution in a heterogeneous format. The invention relies upon the detection of back scattered light from an evanescent wave disturbed by the presence of a colloidal gold label brought to the interface by an immunological reaction. The evanescent wave existing at the interface in turn is the result of a totally internally reflected incident light wave. Placement of the detector at a back angle above the critical angle insures a superior signal-to-noise ratio. Apparatus and methods for scanning, detecting and manipulating light including a scattered total internal reflectance immunoassay system are provided.

Reflection and trapping of transient Alfven waves propagating in an isothermal atmosphere with constant gravity and uniform magnetic field

Abstract: A time-dependent linear magnetohydrodynamic numerical model was used to investigate the propagation of Alfven waves in an isothermal and stratified atmosphere with constant gravity and uniform vertical magnetic field. Results show that the Alfven wave transit time for the wave source to infinity is finite and that the wave exhibits continuous partial reflection which becomes total reflection as the front approaches infinity. The total reflection causes the waves to be trapped in the cavity that extends from the wave source to infinity and in which the wave energy is stored. The results suggest that the reflection of Alfven waves (of sufficiently long period) from the outer corona is an intrinsic phenomenon for any stellar atmosphere stratified by gravity and an open magnetic field, and that, therefore, such waves may be trapped in the stellar atmosphere.

Fabrication of diffractive–reflective optical interconnects for infrared operation based on total internal reflection

Abstract: Diffractive–reflective optical interconnects (DROIs) for optical chip-to-chip interconnection were introduced in a 1988 paper. In this paper we demonstrate the use of total internal reflection for guiding the light inside the glass plate. The required holographic grating couplers were produced by expoiting the wavelength change from blue light recording to red light reconstruction. Several types of fan-out DROI have been made in dichromated gelatin.

Critical angle measurement of elastic constants in composite material

Abstract: Application of critical angle measurement for determination of elastic constants of composite materials is described. For general orientation of the composite material relative to the plane of incidence, three critical angles exist, for quasilongitudinal and fast and slow quasitransverse waves. It is shown that, for any two‐dimensional composite material, the critical angles are directly related to the phase velocities of bulk waves in the sample plane. A simple and novel type of goniometer is developed for these measurements which utilize a cylindrical reflector for measurement of the double reflection coefficient. The values of the elastic constants are reconstructed from the measured velocity surfaces by using nonlinear least‐squares optimization fitting. Analytical relations between ultrasonic velocity and elastic constants valid for arbitrary anisotropy are implemented in the fitting optimization.