Showing papers on "Total internal reflection published in 1970"

Observation of Waves Radiated from Circular Cylinders Caused by an Incident Pulse

Abstract: Schlieren visualization and hydrophone measurements are used to observe the radiated wavefronts which result when an acoustic pulse is incident on a metal cylinder in water. The range of size parameter ka from 138 to 1419 is considered. The wavefront positions are traced by the refraction, internal reflection, and radiation of shear and compressional waves. In the case of solid cylinders, many wavefronts display an apparent circumferential property derived from the incidence of energy from the normal to the appropriate critical angle. Identification of one of these wavefronts as resulting from previously identified “Rayleigh‐type” wave propagation and a single incident angle is denied, although the circumferential property is verified. A previously identified faster circumferential wave is attributed to a composite wavefront resulting from direct compressional transmission and an increasing number of its internal reflections. Other wavefronts depending on mode conversions are also identified. A mechanism ...

Propagation constants of resonant waves on homogeneous, isotropic slab waveguides.

Abstract: A general graphical study of the complex valued propagation constants, defining the various types of TE waves that are resonant on optical thin-film (slab) waveguides, is presented. The dielectric constants of both the slab and its surroundings are allowed to take on all possible complex values. The corresponding waves are classified in to two general types: surface waves, with conductive losses only; and leaky waves, with both conductive and radiative losses.

Diffraction and channeling

Abstract: A review of the scattering of fast charged particles by crystal lattices in terms of both classical and quantum mechanics is presented and a contrast and comparison of the two approaches is made. The anomalous transmission and absorption phenomena of the Borrmann effect of diffraction are analogs of channeling and blocking, which appear as classical mechanical effects in a mass independent limit. For conditions which correspond to localization of a wave packet in the crystal, accompanied by the elimination of observable diffraction effects, all features of the quantal model become analogous features of the classical model. The patterns seen in reflection, and in transmission with either thin or thick crystals, are then dominated by mass independent critical angles, commensurate with the disappearance of Planck's quantum of action and with the appearance of the laws of geometrical optics. An experimental study of the transmission of low energy protons through single crystals of gold is described and the different effects obtained for thin and thick specimens, analogous to those obtained in diffraction, are discussed. A consequence of the replacement of the extinction distance and the Bragg angle by a continuum of values for the orbital wavelength and critical angle respectively is that of a new phenomenon, referred to as quasi-channeling, which violates continuum potential concepts. It is proposed that quasi-channeling can give rise, in the best circumstances, to an oscillatory Rutherford scattering yield with depth in the `shadow' behind a crystal surface, analogous to the Pendellosung effects of diffraction, and to an additional yield due to scattering in the wake of point or clustered crystal defects.

Multiple reflection of plane SH waves by a dipping layer

Abstract: The problem of a plane SH wave incident at the base of a dipping layer has been considered. A solution by multiple reflection for waves incident at any angle perpendicular to strike has been obtained for the amplitude, phase and phase velocity. Numerical values are calculated on the surface. For waves propagating in the up-dip direction the amplitude versus frequency curves for a constant depth to the interface change slowly with increasing dip for dip angles less than 20°. However, for waves propagating in the down-dip direction, the character of the amplitude curves changes rapidly. It is found in these cases that the diffracted wave plays an important role. In addition to satisfying the boundary conditions at the surface and between the media, the diffracted wave must also satisfy additional conditions along a dipping surface lying between the free surface and the boundary between the two media due to the geometrical nature of the reflected wave solution. It is found that the phase velocities vary rapidly with both period of the wave and depth to the interface, particularly for propagation directions close to an angle which corresponds to vertical incidence in the horizontally layered case.

Apparatus and method for measuring the carrier concentration of semiconductor materials

Abstract: Technique of measuring the free carrier concentration in a silicon specimen by passing a beam of infrared or far infrared energy from a laser through a body of intrinsic germanium to impinge on a surface of the silicon specimen which contacts the germanium at an optically flat interface. The angle of incidence is varied until substantially all of the incident radiation is reflected and detected by a photodetector. This angle of incidence is designated the critical angle and is a measure of the carrier concentration of the silicon specimen.

Optical Properties of the Linear Critical-angle Refractometer

Abstract: The construction of several forms of a new type of critical-angle refractometer with a linear scale has been described elsewhere by the author. In the present paper its optical properties are considered in more detail; it is shown to be surprisingly free from aberrations, the accuracy of measurement using monochromatic light being limited only by diffraction. The conditions for achieving this accuracy and the factors affecting the contrast of the cut-off edge are discussed.

Internally reflecting barrier control filtering apparatus

Abstract: Filtering apparatus is provided for isolating a very narrow optical frequency range in the order of a spectral line width. Features include a fixed geometry of a light input member relative to a barrier member as well as an appropriate selection of the media of these two members. The media of the input member can be any material that is more refractive than the barrier member and it has a flush interface with the barrier member disposed at such an angle that the interface angle of incidence is greater than the critical angle of the two members. Thus, all light wavelengths other than the wavelengths of particular concern, are internally reflected in the input member. To permit the desired optical frequency bank to pass, the barrier member is formed of a media having a capacity for absorbing input light in the immediate vicinity of a wavelength that falls within the narrow frequency pass band. The absorption produces an irregularity in the refractive dispersion curve for the barrier media. When the angle of incidence and the interface of the input and in barrier members is fixed sufficiently close to the critical angle for this interface, the irregularity varies the relative refractive index sufficiently to vary the relationship of the critical angle with the angle of incidence and permit the narrow band to pass into the barrier member and on into the output member.

Non-destructive determination of carrier concentration in epitaxial silicon using a total internal reflection technique

Abstract: A non-destructive optical technique of determining free-carrier concentration in epitaxial silicon layers is described. The extinction coefficient and the refractive index of a semiconductor vary with its free-carrier concentration. The changes in these parameters were used to determine the carrier concentration in the material by measuring the total internal reflection from the surface through a higher-refractive-index medium. Calculations are given for reflectivity on n-type silicon and for the dependence of extinction coefficient and refractive index on the free-carrier concentration of n-type silicon at wavelengths of 3.39 μm and 10.6 μm. Measurements were made on n-type bulk and epitaxial silicon using a helium-neon laser beam at a wavelength of 3.39 μm. The experimental data correlate well with the theory. The sensitivity of the technique is limited to the concentrations of about 1 × 1017 atoms/cm3 in n-type silicon using 3.39-μm radiation; however, the range can be extended to about 1 × 1016 atoms/cm3 using 10.6-μm radiation. Effects of the specimen surface and the effective mass of the material on these measurements are discussed.

Enhancement of the Longitudinal Kerr Magneto‐Optic Effect in Thin Films

Abstract: This paper reports on the observation of substantial rotation and reflection enhancements with thin magnetic films evaporated on the base of high index prisms with films of suitable index on only the air side of the magnetic thin film. Angles of incidence at the prism‐magnetic thin‐film interface were near the critical angle for total internal reflection. The magnetic film thickness and the thicknesses and indices of the dielectrics were obtained with the help of a computer program which calculated the reflection coefficients as well as the Kerr rotations and energy mode transfer. Enhancements of rsp up to a factor of 20 were obtained.

Transient Wave Reflection From Inhomogeneous Plasmas

Abstract: Distortion of an electromagnetic pulse undergoing total internal reflection in inhomogeneous isotropic plasmas with special reference to the lower ionosphere has been investigated. The initial transient response and buildup of the reflected signal for different angles of incidence has been numerically investigated. It is seen that the signal builds up more rapidly for larger angles of incidence, and the dispersion is maximum for normal incidence of the pulse. This observation is in qualitative agreement with the experimental observations of Schmitt (1965) for uniform plasmas.

Prism reflectors for high power lasers

Abstract: A new type of laser reflector is described in which the laser beam is split by frustrated total internal reflection and the components combined again. It has the properties of high reflectivity, high damage resistance, wide bandwidth and variable reflectivity. The design of two particular reflectors is discussed and their performance evaluated. One of these reflectors has the property of lateral inversion of the reflected beam, which is found to aid transverse mode selection in a ruby laser. As an application of the reflectors, a damage free, single transverse mode, mode-locked ruby laser is described.

Arrangement and process for measuring the refractive index of liquids

Abstract: A two-beam arrangement for measuring the refractive index of liquids using the fact that the intensity of a measuring light beam reflected at an interface between a solid reference body and a sample liquid is governed by the refractive index of the sample liquid when the angle of incidence of the light beam striking the interface is smaller than the critical angle of total reflection, in which arrangement the measuring beam and comparison beam are reflected at the same point along an interface between a measuring liquid sample and a reference body, the angle of incidence of the measuring beam being smaller and the angle of incidence of the comparison beam being greater than the critical angle of total reflection.

Silicon p-i-n photodetector using internal reflection method

Abstract: A semiconductor photodetector is proposed which makes use of an internal reflection method to enhance the photoresponse. This method is to let the incident light be multiply-reflected in the detector so that a long distance is traveled and most of the photon energy is absorbed by the detector. Theoretical analysis of the steady-state and time-dependent photoresponses for a p-i-n photodetector is presented. The photodetector is found to be particularly useful in detection of light with wavelengths near the intrinsic absorption edge. The photodetectors are fabricated from 4000 Ω.cm n-type, oriented silicon wafers. Both sides of the wafer are polished with one side inclined one-half degree with respect to the other. The p + n junction and the ohmic contact are formed by alloy method. The measured photoresponses for wavelengths of 1.0 and 1.1 µm are in reasonable agreement with the theoretical predictions.

Improvements in or relating to refractometers

Abstract: 1209036 Critical-angle refractometer NATIONAL RESEARCH DEVELOPEMENT CORP 14 June 1968 [19 June 1967] 28275/67 Index G1U 18 [Also in Division G4] A refractometer comprises a block of transparent material 3 with a concavity in the surface in the shape of the curved portion of a cylinder, which measures the refractive index of a liquid by bringing the curved portion 10 into contact with the liquid and observing the said curved portion with observing means by means of light coming only from a direction perpendicular to the axis of the cylinder. Light from a source 1 is reflected by total internal reflection at a 45 degree face 2 down a transmitting section of the block 3 in the form of a rod of polymethylmethacrylate which is divided into two sections 5 and 6 by an opaque screen in the form of a longitudinal saw cut 7 filled with an opaque plastics material. The end portion of the block has a bevel surface 8 painted white and an aluminized bevel surface 9 both at 45 degrees to the axis of the block and an inner cylindrical surface having its axis parallel to the longitudinal axis of the block. The bevel 8 has its lower edge 11 coinciding with the projection of the screen 7 to reflect the light diffusely from the transmitting section 5 of the rod 3 on to the cylindrical surface of the rod in such a manner that it is reflected by total internal reflection from the cylindrical surface 10. The light is then specularly reflected by the bevel 9 and leaves the receiving section 6 of the rod 3 via a magnifying lens 12 and a small exit pupil 13. The image of the bevel 8 seen through the lens 12 is cut off at a position related to the refractive index of the liquid under test and the value of this refractive index can be read off a scale which may be engraved on the cylindrical surface 10 or preferably is in a flat plane at an apparent distance from the eye-piece such that there is no parallax between the scale and the image of the bevel. The scale may be a graticule (121) Fig. 12 (not shown) at the top of the block viewed by reflection of a metallized strip (122) on the base or it may be in a pit (121) Figs. 13, 14 (not shown) and may be viewed directly Fig. 14 or by reflection Fig. 13, or a graticule may be positioned in the eyepiece of a compound microscope. In a modification Fig. 7 (not shown) the shaped end portion 4 of the rod 3 as shown in Fig. 1 is replaced by separate block of material (71) the material being chosen so as to have a value of its refractive index greater than that of the liquid to be measured. Bevels 8 and 9 are formed on the block (71) and act to transmit and receive light into and from the block of material (71) in the same manner as before. In yet another embodiment Fig. 8 (not shown) a separate block of material (81), similarly to the block of material (71) is attached to an opaque supporting rod (82). In this case light is transmitted into and received from the block (81) by means of polymethyl methacrylate sheets (83 and 84) respectively which are attached to the opaque supporting rod (82). The surfaces that are not used optically are painted matt black to reduce reflection. This arrangement may be used to measure the state of charge of a battery. In an alternative embodiment Fig. 9 a cell or a part of a conduit has a transparent wall 92 with one opalescent face 93 illuminated by an extended light source. Light is reflected through the edge 95 and cut off as before, a scale engraved on the face 93 giving a measure of the refractive index of a liquid in the conduit. Walls of material of different dimensions or quality may be made to study the variations in refractive index with depth to reduce the parallax error. The scale can be observed using a fiducial line to line up the observers's eye or through a coherent fibre optics viewing system. An electrical output signal may be obtained by observing the image with a photocell or a stack of sheet light guides each one of which has a photo-cell associated with it. A second method is to use a split cathode photo-cell which is arranged to lock on a mask carried on a moving pointer to the boundary between the light and dark areas. A third method gives a bright line at the demarcation edge which is observed through a digitizing mask. A mask 181 Fig. 18 with two holes 182, 183 is placed against the face 93 and a combination of total internal reflection and refraction through the liquid gives the pattern shown in (c) and the two light areas are superimposed to provide a narrow bright line the range of values that can be measured may be increased by stacking a number of arcs (191) of increasing cylindrical area, Fig. 19 (not shown) and by providing more than one direction for viewing. If the refractometer is to be used with a very turbid liquid the surface 10 may be illuminated through the liquid.

Improvements relating to the examination of ground surfaces

Abstract: 1,214,201. Beam Splitters. HAWKER SIDDELEY DYNAMICS Ltd. May 27, 1969 [March 1, 1968; May 27, 1968], Nos. 10186/68 and 25284/68. Heading G2J. [Also in Division G1] In an arrangement for examining the ground edge facets of a razor blade a beam of coherent light is used to illuminate the edge and the reflected beams are used to determine the angles and widths of the facets by means of photodetectors. Beam 20 of coherent light is made to traverse path (a) and (b) alternately by means of split prism SP rotating about an axis normal to the paper. Beam (a) illuminates the whole width of the facets 13, 13a and reflects a beam 21 to detector P. Since the angle of the incident beam changes linearly with time; joints 24, 24 1 being conjugate with request to lens L2, the output beam rotates about the edge of the blade at substantially constant rate so that the angle of the facets can be determined. Beam (a) is produced by total internal reflection occurring in the prism. When the prism rotates further the beam passes through and is reflected by mirror M onto the edge of the blade. This beam travels at substantially constant rate across the facet and is detected at P1, P2 so that the facet width can be determined.

Refraction and reflection of ultrasonic surface waves by thin-gold-film layers on lithium-niobate substrates

Abstract: Acoustic-surface-wave phenomena similar to optical refraction and total internal reflection have been observed in thin metal prisms deposited on y cut lithium niobate. In addition, scattering of the surface waves has been observed both at the boundaries and interior of the gold-film prisms. The observed total internal reflection and refraction angles were found to agree with theoretical predictions.