Showing papers on "Total internal reflection published in 1991"

Microscope at the Brewster angle: Direct observation of first‐order phase transitions in monolayers

Abstract: A microscope employing the characteristics of the reflection at the Brewster angle has been built for the study of first‐order phase transitions in monolayers and the growth of two‐dimensional domains without adding fluorescent impurities. It takes about 2.4 s to constitute an image.

Internal reflection of diffusive light in random media

Abstract: The consequences of internal reflection of multiply scattered light at the boundaries of disordered media are studied We show that the effect of internal reflection due to index mismatch can be quantitatively accounted for with a single parameter by incorporating a reflection coefficient into the boundary condition for the diffusive light We measure the angular correlation functions in transmission and reflection at different thicknesses for both high- and low-index mismatch By including the effect of internal reflection, we are able to obtain consistent quantitative agreement between experiment and theory Extensions to other experiments including diffusing-wave spectroscopy, coherent backscattering, frequency correlations, and pulse propagation are discussed

Apparatus and method for detecting the presence of gas in a borehole flow stream

Abstract: A borehole apparatus detects the presence of gas within a formation fluid sample. A light source transmits light rays to an interface between the fluid sample and the flow line. The interface reflects the light rays toward a detector array. The detector array detects light rays having angles of incidences extending from less than the Brewster angle to more than the critical angle for gas. A data base stores information concerning the Brewster angle and critical angle of gas for a plurality of gas volume categories. A processor determines the percentage of gas present in the formation fluid sample and categorizes the fluid sample as high gas, medium gas, low gas, and no gas based on the signal from the detector array and the information from the data base.

An atomic trap based on evanescent light waves

Abstract: A new type of gradient light trap is suggested for neutral atoms, based on the evanescent fields of two laser beams experiencing total internal reflection at a dielectric- vacuum interface A distinctive feature ofthe trap is that its bottom is close to the interface: at a distance of the order of the wavelength of light

Light-emitting diode array with projections

Abstract: A light-emitting diode array in which the light-emitting surface for external output of light from the light-emitting layer is processed to give it a slope, for example, which by increasing the critical angle of the internal reflection between the active layer and the air raises the external light output efficiency.

Total reflection X-ray fluorescence spectrometry for quantitative surface and layer analysis

Abstract: Measurements of X-ray fluorescence spectra versus grazing incident angles provide information on elemental composition as well as density and thickness of near surface layers. Calculations of fluorescence intensities are presented, which are used for the evaluation of data obtained by total reflection X-ray fluorescence (TXRF) spectrometry. The calculation is based on a matrix formalism to account for standing wave phenomena due to transmission and reflection in layered material. For the determination of concentrations the model makes additional use of the fundamental parameter technique in order to include absorption and enhancement effects of the fluorescence radiation. On the basis of experimental data some capabilities of this nondestructive and contactless probing technique are presented.

Polymer thin films and interfaces characterized with evanescent light

Abstract: This paper describes the use of evanescent light for the optical characterization of polymer thin films and interfaces. Firstly, a few basic concepts of evanescent wave phenomena, including total internal reflection, plasmon surface polaritons and guided optical modes, are reviewed. It is shown that the excitation of these waves allows for a sensitive determination of the optical architecture of the interface(s) involved. This “surface light” can then be used for the same broad range of optical techniques as it is known from experimental set-ups designed for the investigation of various optical properties of polymer samples using plane electromagnetic waves, i.e. “normal” photons. This is demonstrated for diffraction experiments, microscopic investigations, inelastic scattering, e.g. Brillouin- or Raman-spectroscopies, etc. The examples given include thin polymer films prepared by spin-coating or by the Langmuir-Blodgett-Kuhn technique. It is shown that properties and processes at solid-solution interfaces can be investigated equally well, and even surfaces of bulk samples can be characterized.

Refractive index measurement of turbid colloidal fluids by transmission near the critical angle

Abstract: The authors describe a modified Abbe refractometer for measuring the optical transmittance across a plane interface from a diffusely scattering turbid sample into a prism. When the prism refractive index exceeds that of the sample, a critical angle is present even when the sample contains particles which are wavelength sized or larger. Hence, the sample refractive index may be measured. However, measurements of transmittance near the critical angle show a poor definition of the critical angle for some samples, with a consequent loss of experimental precision in the refractive index. The method is applied to several polymer latex dispersions and some glass ballotini. For all lattices the measured refractive index varies linearly with latex volume fraction. For all dispersions except one the dependence of refractive index on volume fraction is in good agreement with the theory of refractive index based on Mie scattering by spherical particles.

Ballistic electron transport in semiconductor heterostructures and its analogies in electromagnetic propagation in general dielectrics

Abstract: A comprehensive set of analogies between ballistic electron wave propagation in semiconductors (arbitrary kinetic energy and effective mass) and electromagnetic propagation in general dielectrics (arbitrary permittivity and permeability) is established. The expressions for electron wave propagation, reflection, and refraction are developed and shown to have the same functional form as in electromagnetics, if analogous definitions of electron wave phase and amplitude refractive indexes are used. The reflectivity characteristics such as total internal reflection (critical angle) and zero reflectivity (Brewster angle) are analyzed as a function of material parameters for both general dielectrics and semiconductor materials. The critical angle and Brewster angle results are then applied to electron wave propagation in Ga/sub 1-x/Al/sub x/As, where it is shown that all interfaces in this material will have both a critical angle and a Brewster angle due to differing effective masses across the interface. >

Sample–tip coupling efficiencies of the photon-scanning tunneling microscope

Abstract: The photon-scanning tunneling microscope is the photon analog to the electron-scanning tunneling microscope. It uses the evanescent field due to the total internal reflection of a light beam in a prism, modulated by a sample attached to the prism. The exponential decay of the evanescent field is characterized by the penetration depth dp and depends on the angle of incidence θ, the wavelength, and the polarization of the incident beam. The 1/e decay lengths range from 150 to 265 nm as deduced from the expression of the electric-field intensity in the rarer medium for θ = π/2. If we place another optically transparent medium near the surface, frustrated total reflection occurs. It is shown theoretically and experimentally that, if we choose an appropriate angle of incidence θ(θ ≠ π/2) and change the index of refraction of one of the media, the decay length of the electric field can be extremely small, so that images with an improved resolution can be produced.

Miniature Faraday current sensor based on multiple critical angle reflections in a bulk-optic ring.

Abstract: A novel optical element for a bulk glass current sensor that utilizes the Faraday effect is presented with a demonstrated sensitivity of 1 amp-turn and a flat frequency response in the range of 10–104 Hz. The new sensing element overcomes the problems associated with birefringence in optical fiber current sensors and the requirement to make bulk-optic current sensors in complex three-dimensional topologies.

Fourier transform infrared attenuated total reflection spectra of ion‐implanted silica glasses

Abstract: Fourier transform infrared attenuated total reflection spectra of silica glasses implanted with Si or P were measured using a Ge as an internal reflection element. Calculated penetration depth of the infrared radiation is 0.2–1.0 μm depending on the wavelength. These values are comparable to the depths of ions implanted at conventional acceleration voltages. Upon implantation the frequencies of ω4(LO) and ω4(TO) shifted to lower energy, whereas ω3 moved to higher energy. This opposite direction of the frequency shift was explained by a decrease in the Si‐O‐Si bridging angle, which is caused by ion‐bombarded compaction. The magnitude of frequency shifts observed were much larger than that in thermally compacted silica glasses reported so far, showing that an extremely high fictive temperature state is realized in the implanted silica glass layers.

Apparatus for performing fluorescent assays which separates bulk and evanescent fluorescence

Abstract: This invention uses the evanescent wave detection of particles to distinguish bound from free in an analyte-binding assay. Illumination below the critical angle is employed, and a beveled window is used to eliminate bulk fluorescence from the emitted evanescent wave liquid. The sample is held in a non-rigid film cuvette.

Angled optical fiber input end face and method for delivering energy

Abstract: A fiber optic treatment probe (10) delivers laser light from a laser light source (11) through a diffuser (26) An input end face (30) of the fiber is angled with respect to a plane (36) normal to an optical axis (18) of the fiber The end face angle is selected to excite desired modes of the fiber without exceeding the critical angle of the fiber, thereby producing a desired light output from the diffuser

Planar and other waveguide refractive index sensors using metal cladding

Abstract: A species-specific metal clad segment (18) on a waveguide, including a planar waveguide (12), allows controlled light leakage of light propagating through the waveguide by total internal reflection, to measure refractive index and identify chemical species. A waveguide sensor (10) is designed for a particular chemical species by selecting a metal clad (18) with an affinity for the species and by matching the refractive indexes of the waveguide body, clad, metal clad segment, and chemical species. Dual or multiple measurement methods use a pair of multiple metal clad segments of different specificity. The metal clad segment (18) may include another material to provide a suitable refractive index while having the desired affinity for the chemical species or to provide a catalyst to react the species to form a reaction product which is more readily detected.

Theory of near-critical-angle scattering from a curved interface

Abstract: A new type of diffraction effect, different from the standard semiclassical ones (rainbow, glory, forward peak, orbiting), takes place near the critical angle for total reflection at a curved interface between two homogeneous media. A theoretical treatment of this new effect is given for Mie scattering, e.g., light scattering by an air bubble in water; it can readily be extended to more general curved interface problems in a variety of different fields (quantum mechanics, acoustics, seismic waves). The relatively slowly varying Mie diffraction pattern associated with near-critical scattering is obscured by rapid fine-structure oscillations due to interference with unrelated ``far-side'' contributions. These contributions are evaluated and subtracted from the Mie amplitudes to yield the relevant ``near-side'' effects. A zero-order transitional complex angular momentum (CAM) approximation to the near-side amplitude is developed. The most important contributions arise from partial and total reflection, represented by two new diffraction integrals, designated Fresnel-Fock and Pearcey-Fock, respectively. The total reflection contribution is strongly affected by tunneling, giving rise to a generalized version of the Goos-H\"anchen shift. In terms of short-wavelength asymptotic methodology, in a generalized Huygens-Fresnel-type integral representation, the new diffraction features arise from nonanalyticity of the integrand amplitude function within the range of a saddle point. Also discussed are the WKB approximation, a known physical-optics approximation, and a modified version of this approximation: they are compared with the ``exact'' near-side Mie amplitude obtained by numerical partial-wave summation, at scatterer size parameters (circumference divided by wavelength) ranging from 1000 to 10 000. It is found that the physical-optics approximations lead to large errors in the near-critical region, whereas the zero-order CAM approximation is in good agreement with the exact solution, accounting for the new diffraction effects in near-critical scattering.

Kinetics of epidermal growth factor/receptor binding on cells measured by total internal reflection/fluorescence recovery after photobleaching.

Abstract: Total internal reflection fluorescence (TIRF) microscopy is used to measure the dissociation kinetic rate of fluorescein-labeled epidermal growth factor from its specific receptors on the surface of intact but mildly fixed A431 human epidermoid cells in culture. Prior applications of TIRF microscopy have been limited to nonreceptor binding or to model membrane systems. The evanescent field excites fluorescence selectively at the surface of the cell proximal to the coverslip. “Prismless” epiillumination TIR is employed to avoid space limitations and is achieved by passing the excitation laser beam through a high (1.4)-aperture objective so that the light is incident at the glass/water interface beyond the critical angle. Long-term focus is maintained by a special feedback system. Of the possible effects that can influence the time course of the postbleach fluorescence recoveries—the EGF/receptor dissociation ratek 2, the bulk solution diffusion rate of EGF, and the cell surface motion of the receptors—we infer that the dissociation ratek 2 dominates. Several fitting schemes are compared and indicate the presence of a multiplicity of values fork 2, ranging from about 0.05 to 0.004 s−1, with an average value of about 0.012 s−1. These results compare well with values previously obtained by radiolabel/washing techniques. The significance of the results in terms of kinetic models and the advantages of the TIRF technique for these sorts of measurements are discussed.

Chemistry and Technology of Evanescent Wave Biosensors

Abstract: The purpose of this chapter is to describe fiberoptic biosensors, particularly in relation to the evanescent wave. The basic optical properties of fibers, the configurations of fiberoptic biosensors, the means of attaching biomolecules to optical surfaces, advances in fiberoptics, and related fields of interest are described. More detailed discussions of some of the topics are found in other chapters in this volume.

Electromagnetic Wave Reflection and Transmission at a Chiral-dielectric Interface

Abstract: Reflection and transmission of electronmagnetic waves at a chiral-dielectric interface are analysed for normal and oblique incidence and for critical angles. Graphs of the reflection and transmission coefficients are given for various parameters of the two media as a function of the angle of incidence. The results of the analysis and the behaviour of the graphs are discussed and conclusions are drawn from this discussion.

Reflection and Transmission of Plane Waves at the Planar Interface of a General Uniaxial Medium and Free Space

Abstract: A general uniaxial medium is characterized by its permittivity and permeability tensors having the same preferred axis. The plane wave reflection and transmission characteristics of a planar interface between free space and a general uniaxial medium have been obtained; since application as a polarizer is envisioned, the preferred axis lies in a plane parallel to the interface. Application of the Brewster law, as well as conditions for total reflection are explored.

Simple interferometer for evanescent field refractive index sensing as a feasibility study for an immunosensor.

Abstract: We describe a fiber optic interferometric refractive index sensor to illustrate that, by using the evanescent field of an optical waveguide, a potentially very sensitive determination of changes in the refractive index on the waveguide surface can be obtained. These changes can, e.g., be the result of immunoreactions. We used a Mach-Zehnder interferometer configuration with a flow-through cuvette in one arm with a decladded multimode glass fiber of 0.6-mm diameter and 2-cm interaction length. The obtained resolution in measuring refractive index changes is 1 × 10−3. We also developed the theory describing the sensitivity of this sensor using the modal and the geometrical ray description.

Optoelectronic interconnection based on a light-guiding plate with holographic coupling elements

Abstract: An optoelectronic interconnection based on volume-holographic coupling elements located on a thick light-guiding glass plate has been realized. Diode lasers and pin diodes were used as optoelectronic converters. The holographic coupling elements were recorded in dichromated gelatin and aligned on the surface of a glass plate. The light was guided by total internal reflection inside the glass plate. The system performance has been tested at a data rate of 500 Mbit/s per channel. A total loss of 2.6 dB in the optical system and a signal to noise ratio of more than 28 dB were measured.

Electro-optic attenuated total internal reflection modulator and method

Abstract: Method and apparatus for electro-optically modulating the intensity of an incident light beam including a coupling prism with a high reflective index, a semiconductor substrate in optical contact with the coupling prism and having a conductive area formed therein, an organic electro-optic film formed on the substrate and covering at least a portion of the conductive area, and a transmission line disposed above the electro-optic film and cooperating with the conductive area to form electrodes for use in applying an electric field across the electro-optic film. Light directed through the substrate by the coupling prism couples with surface plasmons at the film-to-metal interface and is selectively reflected or absorbed depending upon whether or not an electric field is applied.

Nanosecond laser‐induced cavitation in carbon microparticle suspensions: Applications in nonlinear interface switching

Abstract: Nanosecond transmission to total internal reflection switching has been demonstrated using a thin absorbing film of carbon microparticles suspended in ethanol. The switching results from laser‐induced cavitation and the large refractive index mismatch that occurs when the vapor bubble meets the surrounding glass substrate. This extraordinarily large refractive index change (≳0.3) causes the incident beam to be totally internally reflected at the glass‐vapor interface. Switching energies below 1 μJ have been measured using a 5 ns doubled Nd:YAG laser (λ=0.532 μm) pulse. We have investigated the effects that particle concentration, film thickness, and bias temperature have on switching performance.

Critical angle light scattering from bubbles: an asymptotic series approximation.

Abstract: The critical scattering angle at 82.8° from an air bubble in water locates the transition from partial to total reflection from elementary geometrical optics. The irradiance scattered into a narrow angular region near the critical scattering is a monotonically increasing function of bubble radius a provided a ≫ λ, and the weak contributions from rays reflected internally from the far side of the bubble are neglected. The asymptotic series for critical angle scattering derived here leads to a simple approximation for the irradiance. It also describes the breakdown of elementary geometrical optics for reflection at the critical angle from a curved surface. The leading correction to the scattering amplitude relative to the perfect reflection amplitude is found to be O(β−1/4), where β = 2πa/λ is the size parameter and λ is the wavelength of light in water. The series is confirmed by comparison (as a function of β) with smoothed Mie computations. The leading correction is significant for β as large as 20,000, and it is larger when the light is polarized with the E field parallel to the scattering plane rather than perpendicular to it. The dependence on β−1/4 is also shown from an average of the reflection coefficient over a Fresnel zone. Applications to optical bubble sizing are noted, and the nature of approximations in previous physical-optics models of critical angle scattering is clarified.