Showing papers on "Total internal reflection published in 1981"

Light dispersive optical lightpipes and method of making the same

Abstract: The optical lightpipes are provided with an internal structural configuration which enables the pipes to either transmit light with greater efficiency or to emit light more effectively along the length of the lightpipe. For light emission, light transmitting optical fibers are doped in the core region with refractive and/or reflective light scattering particles. When with a single optical fiber lightpipe, ribs are formed on the exterior of the lightpipe to prevent the lightpipe from being deformed to an angle greater than the critical angle for light conductance. A single tubular lightpipe of plastic may be formed with an internal reflective layer and outer ribs to control bending of the pipe.

Total internal reflection microscopy: a surface inspection technique

Abstract: Structure at and near the surface of a transparent sample or in a film on a transparent substrate can be observed by illuminating the sample from within using a well-collimated polarized laser beam incident at an angle equal to or greater than the critical angle of the sample material and examining the air side of the surface using an optical microscope. Although the technique is similar to dark-field microscopy, additional information can be obtained here concerning the size and depth of scattering sites on or near the surface. This technique, total internal reflection microscopy (TIRM), is complementary to phase contrast (Nomarski) microscopy. Two TIRM microscopes are shown, one of which is used as an attachment to a commercial Nomarski microscope and the second of which is used in laser damage measurements. This surface inspection technique had been used to study surface polishing and cleaning methods, laser damage nucleation sites, ion milling of optical surfaces, and thin film inclusions. A biological application for liquid medium studies is suggested. A description of the electric fields present at and near the air sample interface is given.

Total and partial reflection from the end of a parallel‐plate waveguide with an extended dielectric slab

Abstract: This investigation concerns a TEM wave obliquely incident onto the open end of a parallel plate wave guide with a truncated upper plate. The lower plate as well as the dielectric slab between the two plates is assumed to extend out indefinitely in order to support the propagation of at least one surface wave mode. Reflection from the wave guide opening is determined as a function of incident angle via a dual Wiener-Hopf formulation. It is found that total reflection, i.e., a reflection coefficient with magnitude equal to unity, is possible for incident angles greater than the critical angle associated with the lowest-order surface wave mode of the grounded dielectric slab. The field external to the parallel plate wave guide in this case becomes completely evanescent in the cross-sectional plane perpendicular to the plane of incidence, which is determined by the propagation direction of the incident wave and the edge of the upper plate. It is shown that the phase of the reflection coefficient thus obtained can be used to construct the modal equation for the fundamental mode(s) of a wide microstrip.

Mie scattering near the critical angle of bubbles in water

Abstract: Mie-scattering algorithms were used to compute scattered intensities and phase differences for air bubbles in water. Results are plotted as a function of the scattering angle ϕ in the general range of 30–90° for size parameters ka of 25, 100, 1,000, and 10,000 (corresponding to radii a ≃ 1.3 μm to 0.8 mm). As ϕ decreases below the critical scattering angle at 82.8°, the intensity increases and undergoes broadly spaced oscillations that are described by a physical-optics approximation developed by the authors in a separate publication. Mie scattering also exhibits finely spaced oscillations.

Quantitative ATR spectroscopy: some basic considerations

Abstract: A comprehensive treatment of ATR spectra on the basis of the Lorentz-Lorenz law and Fresnel equations is given. The standard equation for the effective thickness is redefined showing how the lossy case deviates from the lossless case. A matrix effect due to the influence of the real part of the refractive index within an absorption band is demonstrated theoretically as well as experimentally. The concentration of a nonabsorbing solute sample, i.e., glucose, is determined by ATR spectroscopy near the critical angle.

Scattering by a bubble in water near the critical angle: interference effects

Abstract: A physical-optics approximation is derived for light scattering by dielectric spheres with refractive indices less than their surroundings, and it is applied to air bubbles in water. The approximation gives the coarse structure in the scattering when the scattering angle ϕ is near the critical scattering angle ϕc, where ϕc ≃ 83° for bubbles in water. Diffraction has been observed to be important in the critical region because of an abrupt change in the amplitude of the reflected wave [ P. L. Marston , J. Opt. Soc. Am.69, 1205– 1211 ( 1980)]. Interference that is due to a refracted wave produces oscillations in the intensity with an angular quasi-period of magnitude (λ/a)1/2 rad near ϕc, where λ is the wavelength and a is the radius. Unlike diffraction-related oscillations, the interference oscillations increase in magnitude as forward scattering is approached. Optical tunneling through bubbles is also discussed.

Total Internal Reflection Raman Spectroscopy

Abstract: Feasibility of total internal reflection (TIR) Raman spectroscopy as a new tool for characterizing thin surface layers has been investigated, starting with selection of the material for the internal reflection element (IRE). Sapphire was found to be the most suitable for the IRE among TiO2, SrTiO3, several kinds of flint glasses, and sapphire itself. The potential of TIR Raman method was proved by measurements on the two‐layered samples consisting of a thin surface layer of polystryene and a base layer of polyethylene. The thickness of the surface layer that could be measured by the present technique was then extensively investigated for the two‐layered samples which had the surface layer of polystryrene varying in thickness (0.006–0.93 μm) and the base layer of a constant thickness of polycarbonate (12 μm). We could measure vibrational spectra of the surface layers as thin as 0.006–0.2 μm sufficiently separately from those of the base layer. Thickness of the measurable surface layer could be varied to a great extent by changing the incident angle. The observed results were in good agreement with what was deduced from the nature of the evanescent wave.

Small fast large-aperture light modulator using attenuated total reflection

Abstract: An optical modulator is described which offers several advantages in terms of speed, aperture size, and ease of operation over other techniques for amplitude modulation of a collimated light beam. This simple device consists of a prism separated from a metallically reflecting surface by a small micron-size gap. Varying the gap thickness changes the intensity of the light reflected off the base of the prism. The prism acts as a coupler for the excitation of surface plasmons on the metallic surface. This paper explains the principle of operation and presents experimental results obtained on a simple realization of the device.

Modified technique for measurement of orientation from polymer surfaces by attenuated total reflection infrared dichroism

Abstract: : For a sensitive measurement of surface molecular orientation by attenuated total reflection IR dichroism, a modified sample holder was developed utilizing a symmetrical, double-edged internal reflection crystal. This modified sample holder allows the sample to be rotated without the disassembling and reassembling operations which change the contact area between the polymer and the ATR crystal. Therefore, correction of the reflectivities to an internal standard absorption band which is insensitive to orientation is not necessary in this modified apparatus. This was tested on two types of polypropylene. Results with uniaxially drawn polypropylene show that the surface orientation is similar to the bulk, as expected. On the other hand, the orientation as measured by this technique was greater on the surface than in the core of an injection molded polypropylene plate, a tendency confirmed by birefringence. This technique can be used for estimating bulk orientation of a thick sample without sectioning when the surface has similar orientation to the bulk. In cases where the surface differs significantly in orientation from the bulk, our technique should provide a more surface-sensitive estimation than birefringence, since the surface probed is much thinner (only about 1 micron) in this technique. (Author)

Evaluation of reflection interference contrast microscope images of living cells

Abstract: Reflection contrast microscope methods are generally used for studies of those portions of the cell that are turned towards the glass coverslip, to comprehend the structure of the cytoskeleton and the dynamics of cell movement, as well as formation of cell-glass contacts. In incident illumination only reflected light contributes to picture formation. The intensity of which in the case of observation of unstained cells is small because of small refraction differences. To overcome this problem a reflection contrast system was developed by Leitz according to Ploem [49], in which by using contrast preserving measures the reflection becomes prominent in comparison with the lens reflexes. The emerging pictures are a result of interferences of reflections at glass-cell, cell-culture medium and culture medium-cell interfaces. According to Fresnel's equations the reflected intensity depends on the differences of the particular refractive indices and the thickness of the layers, which determine the phase of interfering beams. In idealized systems of thin films the reflected intensity is a measure for their optical constants. Relative reflection measurements from glass-cell areas is comparison with the known glass-medium reflection, can therefore be revealing as far as refraction index, cell-glass distance or cell thickness are concerned. The estimates by Bereiter-Hahn et al. [15] were made in the assumption of vertical illumination neglecting its actual conical shape: the comparison of two Fresnel functions of cytological relevant measurements show - in accordance with Gingell and Todd [24] - that this is only permitted under certain conditions, depending on the required accuracy of the measurements; an incidence angle of about 30 degrees leads to an error of about 10%, an angle of 50 degrees to more than 50%.

Optical measurements of the surface plasmon of copper

Abstract: The optical properties of the noble metal copper are determined by computer fitting the experimentally obtained attenuated total internal reflection (ATR) spectra of its surface plasmon in the visible spectral region (0.42 to 0.63 μm). The dispersion curves of the surface plasmon resonance of copper are determined; they show that the resonance exists on the steep absorption edge of ϵ2 at 2.16 eV. This absorption edge, which is due to the d-band to Fermi level transition, causes the large shift in the location of the surface plasmon excitation from ϵ1(ωs) = −1 to ϵ1(ωs) = −4.7 and causes the true resonance to occur in the complex frequency plane.

Method and apparatus for reproducing optically an information recorded on a record medium along tracks

Abstract: In a method and apparatus for detecting an information signal and a focussing error signal of an objective lens with respect to a video disc on which main and sub beams emitted from a laser light source are to be focussed as light spots by the objective lens, the main and sub beams reflected by the video disc are made incident as parallel light fluxes upon a detection prism surface which is set substantially at a critical angle with respect to the main beam, but at an angle smaller or larger than the critical angle with respect to the sub beam, and two light fluxes of the reflected main beam which situate on respective sides of a boundary plane including the central light ray and perpendicular to a plane of incidence, and are reflected by the reflection surface are separately received by two light receiving regions which are divided along a boundary plane including the main beam reflected by the reflection surface and perpendicular to the plane of incidence. The focussing error signal is derived as a difference between output signals from the two light receiving regions and the information signal is derived as a sum of the output signals from the two light receiving regions. The sub beam transmitted through and refracted by the reflection surface is received by a light detector and a tracking error signal is derived by detecting a variation in a light amount of the sub beam impinging upon the light detector.

Total Internal Reflection Raman Spectroscopy at the Critical Angle for Raman Measurements of Thin Films

Abstract: Total internal reflection Raman spectroscopy at the critical angle has been shown to be useful for Raman measurements of not only thin films but also of any samples that can be directly coated or intimately contacted on the internal reflection element (IRE). Usefulness of this technique was demonstrated for a polystyrene film (0.70 μm thick) coated on the IRE, signal enhancement being 40 as compared with the conventional normal illumination. The technique was also applied to a thin coating layer of bovine albumin on the IRE to give the spectrum of excellent signal/noise ratio.

Luminescent Solar Concentrators

Abstract: Various planar configurations of the luminescent solar concentrator (LSC) are discussed including the uniformly doped, the stacked plate, the thin film, and the multilayered film LSC. Radiation which is lost from the luminescent plate by falling within the critical angle for total internal reflection is examined in terms of the above configurations. A ten parameter efficiency profile has been developed to better evaluate the collector performance and to allow direct comparison with other photovoltaic devices. A collector efficiency of 3.2% is reported and the feasibility of 8 to 10% efficient devices discussed. Several optical distribution factors have been defined and experimentally evaluated for the luminescent plate and associated photovoltaic cell. These factors have been used to calculate a plate-to-cell optical coupling coefficient for two commercially available solar cells. LSCs based on organic and inorganic phos-phor systems are compared and the problem of dye staility discussed.

Molecular Orientation Measurements in Polymers by Infrared Spectral Subtraction

Abstract: The data manipulation ability of a Fourier transform IR spectrometer is exploited to characterize molecular orientation in polymers. In particular, the application of spectral subtraction to dichroic ratio determination and to the measurement of three-dimensional orientation via sample tilting and internal reflection spectroscopy is explored for nylon film samples.

Method and apparatus for recording optically an information signal on a record medium along tracks

Abstract: In a method and apparatus of recording optically an information signal on a disc along tracks by projecting a main beam modulated with the information signal onto the rotating disc by means of an objective lens, in order to obtain focussing and tracking error signals, a sub beam inclined with respect to the main beam is also projected onto the disc by means of the objective lens. The main and sub beams reflected by the video disc are made incident as parallel light fluxes upon a detection prism surface which is set substantially at a critical angle with respect to the main beam, but at an angle smaller or larger than the critical angle with respect to the sub beam, and two light fluxes of the reflected main beam which situate on respective sides of a boundary plane including the central light ray and perpendicular to a plane of incidence, and are reflected by the reflection surface are separately received by two light receiving regions which are divided along a boundary plane including the main beam reflected by the reflection surface and perpendicular to the plane of incidence. The focussing error signal is derived as a difference between output signals from the two light receiving regions. The sub beam transmitted through and refracted by the reflection surface is received by a light detector and the tracking error signal is derived by detecting a variation in a light amount of the sub beam impinging upon the light detector.

Fiber optic transducer

Abstract: A fiber optic transducer is provided by cutting and polishing the ends of two optical fibers, having equal indexes of refraction, at angles with respect to their axis such that all light signals propagating within the optical fibers are incident to the end face at angles that are greater than the critical angle defined for an interface between a medium with an index of refraction equal to the index of refraction equal to that of an intervening medium between the two fibers. The two end faces so cut are positioned to be in a parallel relationship, a distance apart that is less than the wavelength of the light propagating within the input fibers. Variations of this distance with the pressure changes caused by the acoustic environment produces variations in the optical signal energy coupled from the input optical fiber to the output optical fiber, thus creating an amplitude modulated light beam that propagates in the output optical fiber.

X-ray fluorescence analysis in the nanogram region with a total reflected and a Bragg polarized primary beam

Abstract: Improvements of the detection limit in photon induced X-ray fluorescence analysis are obtained by the reduction of the radiation background at constant excitation conditions. Two methods are presented: 1) Bragg-reflection at 2 ν=90° results in a beam linearly polarized and monchromatic. Positioning the detector at an angle 90° to the direction of the polarized beam suppresses the production of scattered photons from sample and sample carrier into the detector. The use of single crystals instead of amorphous scattering materials increases the intensity of the polarized beam, in some cases up to a factor 104. Detection limits and actually used crystal materials and lattice planes for Braggreflection are given in tables. Samples may be of either form, liquid or solid, no special sample preparation is required. 2) The application of X-ray total reflection on the polished and plane surface of a reflector which serves as the sample carrier reduces the radiation background. In the case of X-ray total reflection there is scarcely a penetration of the X-rays into the reflector material. The penetration depth of some 100 A in the reflector-substrate can be compared to an extreme thin foil of same thickness. Therefore the reflector-substrate combines its mechanical strenght, its compact and constant geometric form, its chemical resistance and the possibility of easy handling-with the low background properties of ultra-thin foils. Samples should be liquids where the liquid part of the matrix is evaporated and the remaining trace elements are investigated. Both method are capable of detecting elements in the nanogram region.

Plasma silicon oxide films on garnet substrates: measurement of their thickness and refractive index by the prism coupling technique

Abstract: The prism coupling technique has been used to measure the refractive index and thickness of plasma silicon oxide films deposited on garnet substrates. The film thickness is also measured with a mechanical stylus (Talystep) for comparison. A linearly polarized He-Ne laser at 632.8-nm wavelength or a He-Cd laser at 441.6-nm wavelength is used as the light source in the prism coupler. The use of the He-Ne laser is demonstrated to result in a fluctuation in the detector output due to light interference in the substrate. The He-Cd laser is shown to be superior because the substrate is sufficiently absorbing that interference is eliminated. It also permits thickness measurements on thinner films. The agreement between thickness measurements by the prism coupler and the mechanical stylus is within +/-0.015 microm for films of 0.4 microm or thicker and +/-0.010 microm for thinner films. The error in thickness measurement caused by an error in refractive index assumed or in determining the coupling angles for films thinner than 0.30 microm is also estimated.

Theory of Plane Wave Reflection and Refraction by the Nonlinear Interface

Abstract: This report includes a review of published as well as recent results. In previous papers a new kind of optical bi-stability was proposed which is connected with reflection and refraction of light by a single surface on a nonlinear medium without a resonator or feedback; its first experimental observations were made recently by Smith et al. The main conditions required for its existence are very exact matching of the optical densities of both media and almost grazing incidence of light. These effects are available for positive nonlinearity as well as for negative non-linearity. In the last case, it is possible to excite a new kind of nonlinear wave (longitudinally inhomogeneous travelling waves) which could provide a phenomenon of strong nonlinear parallax of refracted rays along the interface. For more simple observation and some applications of reflection bistability, the use of an electro-optic element as an “artificial” nonlinearity can be proposed; this light-feedback method is analogous to that used in hybrid devices. Our last result is connected with a proposition for a new way to realize reflection bistability which consists of application of single-mode optical waveguides (one of which must be nonlinear) rather than using two semi-infinite media. This allows us to avoid the secondary effects of self-focusing and self-bending of bounded refracted beams of light in a nonlinear medium. At the same time it conserves all features of the main phenomenon of reflection bistability.

Proposed frustrated-total-reflection acoustic sensing method.

Abstract: Modulation of electromagnetic energy transmission through a frustrated-total-reflection device by pressure-induced changes in the index of refraction is proposed for use as an acoustic detector. Maximum sensitivity occurs for angles of incidence near the critical angle. The minimum detectable pressure in air is limited by Brownian noise. Acoustic propagation losses and diffraction of the optical beam by the acoustic signal limit the minimum acoustic wavelength to lengths of the order of the spatial extent of the optical beam. The response time of the method is fast enough to follow individual acoustic waves.

Liquid crystal display device for total reflection switching with fluorescent dye addition

Abstract: Bias dependences for reflectivity curves were measured in the total reflection range for several liquid crystals, and orientation near the boundary was investigated. Incident angle dependences of the transient response for total reflection ON and OFF switching were measured. Fluorescent dye addition effects for total reflection switching were investigated. Using a mixture of the fluorescent dye (coumarin 6) and MBBA + BBCA, a novel display device for a wide viewing angle has been successfully demonstrated.

Device for dividing a laser beam.

Abstract: A device for dividing a laser beam (1), e.g. into parallel equidistant beams (12) includes a glass plate (2) with two opposing planar, parallel surfaces. A transmission grating (3) is arranged on one glass surface. A reflecting layer (4) is applied over the grating (3), and an opening (5) is arranged in the layer (4) at half the length of the plate, for taking the beam (1), which is to be divided, to and through the grating. The laser wave-length and the grating line density are selected to give total reflection at the free surface of the glass for a beam (11) diffracted at the opening (5) of the grating (3). By altering the angle of incidence (Alpha) of the beam (1), the distance a between the subdivided beams can be continuously varied within given limits. The device is also utilizable for combining a plurality of separate beams into a single beam.