Showing papers on "Total internal reflection published in 1980"

Ultrasonic system for measuring fluid impedance or liquid level

Abstract: An ultrasonic system that measures either the impedance of a fluid or liquid level utilizes moderately directional, bulk SV mode sound waves generated by a transducer and propagated in a homogeneous, flaw-free solid member. The SV wave propagates in the solid along a zigzag path that reflects at a solid-fluid interface in at least two areas and at an angle of incidence that exceeds the first critical angle by at least five degrees and is less than the second critical angle by at least ten degrees. The attenuated amplitude of the wave due to acoustic coupling between the solid and the fluid measures the impedance or an impedance related parameter of the fluid. The system preferably includes a second acoustic path that serves as a reference to compensate for changes in parameters such as temperature, the nature of the fluid, the transducer, the transducer coupling, and residues or corrosion at the solid-fluid interface. In another form, the reference mechanism is a series of reflections from notches in the solid member. For liquid level measurement desensitized to variations in the liquid impedance, the solid is an elongated member that is oriented at an oblique angle, or is parallel to, the surface of the liquid. Other liquid level measurement systems utilize multiple receivers or reflectors located at the points of reflection of the zigzag wave.

Touch position sensitive surface

Abstract: A touch sensitive device is arranged with substantially parallel surfaces inside which light from a synchronized source, such as a CRT, can become trapped by total internal reflection. The edges of the device are fitted with photodetectors which respond to the entrapment of light within the surfaces. The top surface is arranged so that a touch of the device at a particular point will cause a medium change on the surface at that point. The medium change causes light to become entrapped within the surface by total internal reflection thus making it possible, by comparing the photodetector output with the CRT raster position, to determine the exact surface position of the touch. Using this arrangement, positional determination is uneffected by raster drift.

Scattering of an obliquely incident acoustic wave by an infinite cylinder

Abstract: Expressions are derived for the scattered farfield pressure which results from the illumination of an infinite aluminum cylinder by a plane acoustic wave, whose propagation direction makes an arbitrary angle, α, with the normal to the cylinder axis. Computations are made at angles between α=0 ° and the Rayleigh critical angle, α=31.3 °. Changes in the scattered field are related to shifts in the paths of geometric and elastic surface waves from circumferential at α=0 °, to helical, to axial Rayleigh surface waves generated at the Rayleigh critical angle.

Frustrated-total-internal-reflection multimode fiber-optic hydrophone.

Abstract: A multimode fiber-optic hydrophone based upon the principle of frustrated total internal reflection has been constructed and tested. The sensitivity of the device to acoustic waves in water is in good agreement with predictions derived from its measured sensitivity to applied static displacements in air. The minimum detectable pressure for the device was 62 dB relative to 1 μPa at 500 Hz. Static displacements as small as 4.8 × 10−3 A can be detected. The sensor is compatible with present multimode fiber-optic sources, detectors, and components.

Die Spiegeloptik des Flußkrebsauges

Abstract: In the superposition eye of the crayfish (Astacus leptodactylus), images are formed by radial plane mirrors arranged in an orthogonal pattern. The optical structure of the crayfish eye can be described as a family of virtual reflecting cone envelopes concentric around each direction in space. There exist two reflection mechanisms: total internal reflection at the sides of the crystalline cones and reflection by multilayer mirrors attached to the distal parts of the cones. Image-forming rays have to be reflected twice in the general case, and once in the case of perpendicular position of the plane of incidence and the mirror plane. For rays incident at small angles to the ommatidial axis, this condition is almost satisfied due to a particular axial variation of the refractive index of the crystalline cone, and for rays incident at large angles, due to the spectral reflecting properties of the multilayer reflector.

Reflection of a Gaussian beam from a nonlinear interface.

Abstract: A numerical analysis of the reflection of a two dimensional Gaussian beam from the interface between a linear and a nonlinear medium is presented. The refractive index of the nonlinear medium is a function of the intensity of the radiation field, having a smaller value than the linear refractive index for zero field intensity. The Gaussian beam is incident from the linear medium and suffers total reflection at low intensity. At sufficiently high intensity nonlinear effects are observed. Above a threshold value the incident beam breaks up into a reflected wave and a surface wave. Once the beam is sufficiently strong for a surface wave to form, its interaction with the boundary becomes surprisingly independent of field intensity; but for very strong fields the reflectivity is increased at the expense of the surface wave. A very different behavior is observed when the refractive index is constrained to remain below a certain maximum value. Now the field detaches itself from the surface and penetrates into the nonlinear medium forming one or more distinct beams. The plane wave theory predicts the existence of hysteresis so that two different solutions should exist for the same physical parameters. A second solution was indeed found in one case with constrained refractive index, but its validity is somewhat uncertain at this time.

A systematic method of estimating the performance of X-ray optical systems for synchrotron radiation. I. Description of various optical elements in position–angle space for ideally monochromatic X-rays

Abstract: The performances of various optical elements are presented for ideally monochromatic X-rays in terms of position–angle space, which is used in the phase-space method. The optical elements discussed are a synchrotron radiation source, flat perfect crystals (reflection and transmission geometries), mosaic crystals, curved crystals of reflection (Johansson, Johann and logarithmic spiral types) and transmission geometries, and an elliptic total reflection mirror. The angular widths of acceptance and emergence for diffraction are properly taken into account in both the flat and curved crystals. It is shown that focusing optical elements such as a curved crystal and an elliptical mirror should not be treated simply as lenses.

Dark field surface inspection illumination technique

Abstract: A method and apparatus for observing imperfections on the surface of and imbedded in an optical sample using a dark field technique. Linearally polarized laser light is entered by a prism-fluid index matching method which causes internal reflection at the critical angle. The internally reflected beam then coherently combines with the incident beam in the vicinity of the sample surface. This results in a standing wave pattern which can be adjusted by changing the laser wavelength, the angle of incidence or polarization to selectively illuminate variously regions at and below the surface. One polarization will have maximum intensity at the surface level while the alternate polarization will have a null at the surface level. Defects within the optical sample scatter light such that it does not reach the surface at an angle equal to or greater than the critical angle. This light is emitted from the sample surface and appears as a pattern of bright spots on a dark background. A viewing piece is used to systematically scan the surface of the sample. Using the above standing wave pattern, it is possible to illuminate the surface with a maximum intensity, to learn the position of optical sample imperfections and to determine the sizes of those imperfections. Placing a drop of oil on the surface of the sample removes surface irregularities as a source of scattered light. The oil drop also permits greater control of standing wave patterns within the sample.

Acoustic resonances and sound scattering by a shear layer

Abstract: The energy reflection coefficient is evaluated numerically for plane waves incident on a plane shear layer having a linear velocity profile. The shear layer is found to exhibit no resonances and no Brewster angles. The behavior of the reflection coefficient depends crucially on the parameter tau, a nondimensional measure of the disturbance Strouhal number with respect to the disturbance Mach number in the mean flow direction. For moderate values of tau, the amplified reflection regime degenerates into the total reflection one, whereas in the ordinary reflection regime the variation of the reflection coefficient with tau depends on whether or not the corresponding vortex sheet has a Brewster angle. The results indicate that caution should be exercised in uncritically modeling a finite thickness shear layer by a corresponding vortex sheet.

Proposed fiber-optic acoustical probe.

Abstract: An optical fiber whose end face is polished to an angle θ close to the critical angle θc is proposed as an acoustical detector probe Since θc can be tuned by optical material dispersion of the glass fiber to bring θc close to θ, probe sensitivity can be controlled Also, tuning would allow the probe to be either phase or amplitude modulated by the acoustical wave, depending on whether θc were tuned to greater than or less than the incident angle θ

Plane electromagnetic waves in moving media and reflections from moving interfaces

Abstract: A general discussion is given of the properties of electromagnetic plane waves in moving isotropic and anisotropic media. This includes working out the general constitutive relations and the dispersion relation for the isotropic case. Treatment of the moving interface involves determining not only the Doppler shifts but also generalization to a moving interface of the law of reflection, Snell’s law, formula for the critical angle, Brewster’s angle, and the reflection and transmission coefficients. The latter involve generalization of the Slater impedances associated with the incident, reflected, and transmitted waves. The maximum angle of incidence in the frame moving with the interface is shown to be that which represents a flow of energy parallel to the interface.

Method and device for quantitative determination of optically active substances

Abstract: 1. A process for the quantitative determiantion of a dissolved optically active substance in aqueous or non-aqueous solutions by means of polarimetry by splitting the light beam after the sample by means of a beam splitter, thereby producing a measuring beam and a reference beam, and forming a difference or quotient signal of the signals of the measuring and the reference beam detected by corresponding detectors, whereby the polarized light of the light source prior to passing through of the sample is eventually subjected to frequency, phase, or amplitude modulation, and the difference or quotient signal formed of the signals of the measuring and the reference beam is demodulated correspondingly, characterized in that for simultaneously obtaining beam splitting and an analyzing effect the light beam after the sample is directed to an optical interface at an incidence angle (alpha) between the polarization angle and the limit angle of total reflection.

Whispering gallery lasers on semi-insulating GaAs substrates

Abstract: Double heterostructure lasers are described in which light is guided by total internal reflection along a dielectric interface formed by the perimeter of an etched mesa. By means of the crowding effect, injection current is restricted to a narrow strip adjacent to the edge of the mesa. This results in the preferential excitation of optical modes which are localized in the vicinity of the dielectric interface. Both half-ring lasers formed at a single cleaved facet and quarter-ring lasers formed at a cleaved corner were fabricated.

Fiber optic transducers

Abstract: A fiber optic transducer for sensing ambient conditions by converting small displacements into light intensity variations comprises first and second optical signal transmission lines (21, 23) each of transparent material with a refractive index n₁ and a planar end face (26, 27) oriented at an angle with respect to the longitudinal axis; means for positioning said end faces (26, 27) in a substantially parallel relationship and separated by a transparent material with a refractive index n₂ less than n₁, a distance (d) that is variably dependent on variations caused by said ambient condition to be sensed, said distance (d) having a maximum of the order of a wavelength, in the separating material, of an optical signal to be propagated in said transmission line; said angle of said end faces being determined such that at least one light ray of an optical signal propagating within said first and second transmission lines (21, 23) is incident thereto at angle of incidence greater than the critical angle for an interface between transparent materials with refractive indices n₁ and n₂, respectively.

Non-imaging optical energy transfer system

Abstract: A non-imaging optical energy transfer system includes a tapered light pipe and associated field lens as its central energy transfer mechanism. The light pipe/lens combination is located between two separate sections of the system which individually have the same throughput or etendue but otherwise differ in f/#, beam focus, and pupil sizes. The transfer system is disclosed used in combination with a circular variable filter-absorption cell infrared spectrometer and an internal reflection spectrometer, employing a multiple internal reflection crystal.

Some Bottom-Reflection Loss Anomalies near Grazing and Their Effect on Propagation in Shallow Water

Abstract: The bottom-reflection loss near grazing from a hard bottom, or from one that has a hard sub-bottom, can in certain cases be fairly high. This can result in higher propagation losses in shallow water than are usually expected. Two frequently observed cases have been studied, one where the bottom can propagate shear waves and another where the bottom is covered by a layer of soft unconsolidated sediments. The first case causes a low-frequency attenuation whereby an optimum frequency is created for the propagation, whereas the second case creates selected frequencies for which the propagation is poor.

Graphical approach to Fresnel’s equations for reflection and refraction of light

Abstract: A coordinate‐free approach to Fresnel’s equations is developed. The method applies to arbitrary transparent media, with light of either s or p polarization, at any angle of incidence. A graphical construction is described for finding the vector amplitudes of the reflected and transmitted waves. Total internal reflection and Brewster’s Law have a simple graphical interpretation.

Electrooptical scanning device

Abstract: An electrooptical scanning device for deflection of an optical beam of light across an image plane. The device comprises a body of electrooptical crystal material and a periodic array of parallel, spaced electrodes associated with one surface of the body. A light beam entering the crystal body is caused to interact with electric fields established at the one surface by step applied voltages to the electrode array that influence the deflection of the light beam at the moment of total internal reflection at the one surface. By varying the magnitude of the applied voltages across the electrodes, a corresponding approximation of a desired phase retardation can be produced along the phase front of the light beam. The phase retardation across the light beam can be designed to produce a linear phase front angled beam or can be designed to produce a curvalinear phase front forming a focused spot at the image plane. With the changing of the magnitude of the applied voltages across the electrode array, the beam or spot may be made to move about or scan across the image plane.

Method and apparatus for detecting focussing error signal of objective lens

Abstract: In a method for detecting a focussing error signal of an objective lens with respect to a video disc on which a light beam emitted from a laser light source is to be focussed as a light spot by the objective lens, a light flux reflected by the video disc is made incident upon a detection prism surface which is set substantially at a critical angle with respect to a central light ray in the reflected light flux, and two light fluxes 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 central light ray 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.

Holography with guided optical waves

Abstract: Waveguide holograms are recorded in a storage material layer covering a planar dielectric waveguide with a guided mode as reference wave. They are also read-out with a guided mode. In the storage material, assumed to have a lower refractive index than the waveguiding film, the fields of the reference and of the read-out wave are evanescent waves.

A Model of the Blue Phase of Cholesteryl Esters

Abstract: A model of the so-called Blue Phase of cholesterogenic liquid crystalline systems is proposed with the molecular axes inclined to the helix axis by a critical angle of 54.74°. This model results in a spherical refraction indicatrix compatible with the lack of birefringence as well as with the cholesteric-like optical properties.

An x‐ray resonator based on successive reflections of a surface wave

Abstract: Total reflection of x rays is considered by expanding the Fresnel coefficient in the grazing angle of incidence, assumed to be much less than the critical angle. A study is made of resonatorlike mirror systems that are capable of changing the direction of the incoming wave by 2π rad. The possibility of modulating the refractive index n=1−δ−iβ and the influence of scattering losses are briefly discussed. A high number of successive reflections may lead to a nonzero limit exp(−π√2 βδ−3/2) for the relative intensity. It is usually more important to have a ’’horizontal’’ reflectivity curve than a high critical angle.

Total internal reflection from nematic liquid crystals

Abstract: 2014 The attenuated total internal reflection (ATIR) conditions for a plane monochromatic wave, incident on the interface flint-glass prism-deformed homeotropic nematic layer with applied d.c. or high frequency a.c. electric field are considered. The theoretical results obtained with the aid of WBK method show that there are two essential conditions for the wave behaviour : the condition for the exponential variations of the electromagnetic wave components and the ATIR condition obtained from the requirement for equality between the moduli of the incident and the reflected amplitudes. Estimates for the influence of the lower limiting glass plate (e.g. the penetration depth of the evanescent wave) are made. The first two terms in the ATIR condition were used in the experiment performed with MBBA films. The surface energy of the liquid crystal molecules interacting with a thin lecithin layer giving a homeotropic orientation was determined to be in the range of 2 x 10-2 erg/cm2. The accuracy of the method is low in the range of deformation angles 0-5° (~ 1°) and higher for the other regions. The total internal reflection measurements give new and important information about the formation of the double electric layers, the inhomogeneity of the electric field and the flexoelectric properties of the investigated liquid crystals. Revue Phys. Appl. 15 (1980) 1307-1321 AOÛT 1980,

Method and apparatus for generating and detecting acoustic surface waves particularly useful in the non-destructive testing of materials

Abstract: A method and apparatus for generating and detecting acoustic surface waves particularly useful in the non-destructive testing of materials. In this method, the acoustic surface wave is generated in the test sample by a generator transducer coupled to the test sample so as to cause the acoustic wave to impinge on it at the required critical angle. The acoustic surface wave is detected by a pair of spaced steel wedges having their narrow ends in contact with the surface of the test sample so as to detect the shear component of the acoustic surface wave and to generate bulk waves in the steel wedges which travel away from the plane of the contact surface to pick-up transducers. In one described embodiment, the steel wedges provide two spaced, rounded-surface, long-line contacts with the test sample; and in a second described embodiment, a three-member contact is provided in which two of the members are defined by rounded-surface short-line contacts of the wedges, and a third, stabilizing contact is provided by a ball.

Examination of laser damage sites of transparent surfaces and films using total internal reflection microscopy

Abstract: This paper describes total internal reflection microscopy (TIRM), a microscopic inspection technique useful in examining the laser-damaged surfaces of transparent samples. In this technique, the surface is illuminated from within the sample with a well-collimated polarized laser beam at an angle of incidence just greater than the critical angle. Since total reflection occurs, the illuminated region appears to be dark when viewed from outside the sample except for scatter caused by surface defects such as laser damage sites. We will describe two instruments used for TIRM inspection of samples. Finally, various damaged regions will be shown as they appear under TIRM inspection and under Nomarski microscopy. It will be seen that the two techniques are complementary, and that, on highly polished surfaces, TIRM shows somewhat more detail than does Nomarski microscopy. All of the damage sites shown will be the result of 1.06-pm, 1-nsec irradiation of fused silica or BK-7 surfaces.

Low frequency sound absorption of orifice plates, perforated plates and nozzles

Abstract: Analyses of impulse time history data from acoustic transmission tests for conical nozzles attached to a pipe show internal reflections from the solid contraction and open area tend to cancel. To gain understanding of the opposing reflections, tests were conducted by replacing the conical nozzles with orifice plates. The primary variable was the open to solid area ratio. Internal reflection coefficient data reveal that, at an area ratio of 10-12%, the low frequency internal reflection is reduced from unity to about 0.2. Based on comparisons of far-field and internal data, acoustic energy is not conserved. Results are presented for complex reflection coefficient and far-field noise for a series of orifice and perforated plate configurations.

Transmissive projection screen

Abstract: PURPOSE:To obtain an image of high brightness over a broad observation range and to suppress a blur in projected pictures, by providing a Fresnel lens sheet substrate at a projector side and a lenticular lens sheet at an observer side. CONSTITUTION:The Fresnel lens surface and lenticular lens surface of Fresnel lens sheet substrate 15 and lenticular lens sheet substrate 16 are opposed to each other, and Fresnel lens sheet substrate 15 and lenticular lens sheet substrate 16 are arranged at the sides of projector 4 and observer 6 respectively. Further, a light scattering material reproducing a projected luminous flux as an image is dispersed in lenticular lens sheet substrate 16. With regard to the thus obtained screen, light from projector 4 incident to the lenticular lens surface of >1 in refractive index from the air of 1 in refractive index, so no total reflection is caused on the lenticular lens surface, so that while the total beam transmissivity is improved, effective light scattering is obtained.