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Showing papers on "Interference (wave propagation) published in 1978"


Journal ArticleDOI
TL;DR: General bounds on the capacity region are obtained for discrete memoryless interference channels and for linear-superposition interference channels with additive white Gaussian noise.
Abstract: An interference channel is a communication medium shared by M sender-receiver pairs. Transmission of information from each sender to its corresponding receiver interferes with the communications between the other senders and their receivers. This corresponds to a frequent situation in communications, and defines an M -dimensional capacity region. In this paper, we obtain general bounds on the capacity region for discrete memoryless interference channels and for linear-superposition interference channels with additive white Gaussian noise. The capacity region is determined in special cases.

804 citations


Journal ArticleDOI
TL;DR: In this paper, the mean sound levels resulting from the interference between direct waves and those reflected from the ground are strongly influenced, especially at frequencies near interference minima, by fluctuations in phase and amplitude of the sound waves induced by propagation through atmospheric turbulence.
Abstract: The mean sound levels resulting from the interference between direct waves and those reflected from the ground are strongly influenced, especially at frequencies near interference minima, by fluctuations in phase and amplitude of the sound waves induced by propagation through atmospheric turbulence. Since it was found experimentally that the correlation length (∠1.1 m) of the meteorological fluctuations is comparable to the separation between the interfering sound paths, previous theoretical work by Ingard and Maling [J. Acoust. Soc. Am. 35, 1056–1058 (1963)] has been extended to allow for partial covariance between the two waves. The theory has been further extended to use the calculations of fluctuations in phase and amplitude of spherical waves, and to include the explicit calculation of the fluctuating acoustical index of refraction from the fluctuating values of temperature and wind velocity. Measurements (1–6 kHz) have been made of the interference spectrum at 15, 30, and 45 m from a point source 1....

69 citations


Journal ArticleDOI
TL;DR: It is shown that the PDI is simple and easy to use and also yields fringes of constant optical path difference similar to those obtained with a Twyman–Green interferometer.
Abstract: A point-diffraction interferometer (PDI) for use in the infrared is discussed. It is shown that the PDI is simple and easy to use and also yields fringes of constant optical path difference similar to those obtained with a Twyman–Green interferometer. The fabrication of the PDI is described, and typical results obtained using the interferometer at a wavelength of 10.6 μm are shown.

58 citations


Journal ArticleDOI
TL;DR: The basic characteristics and instrumentation of the experimental interferometer setup at the Institut Max von Laue - Paul Langevin (I.L.L.), Grenoble are outlined in this article.

44 citations


Journal ArticleDOI
TL;DR: The background in saturation spectroscopy is decreased by balancing the probe beam, in amplitude and phase, against a second probe, using a configuration like a Jamin interferometer, to improve the signal-to-noise ratio.
Abstract: The background in saturation spectroscopy is decreased by balancing the probe beam, in amplitude and phase, against a second probe, using a configuration like a Jamin interferometer. This improves the signal-to-noise ratio. If the phase is adjustable to provide best balance while the laser is tuned, the signal is proportional to the square of the absorption, and the line width is accordingly reduced.

36 citations


Patent
21 Apr 1978
TL;DR: In this article, an approach for the generation and display of interference patterns for the purpose of quantifying the distortion of either a surface or a transmitted wavefront is presented. But the interference pattern is not considered in this paper.
Abstract: Apparatus is disclosed for the generation and display of interference patterns for the purpose of quantifying the distortion of either a surface or a transmitted wavefront. The invention comprises, in one embodiment, means to align the elements comprising the interferometer cavity, means to continuously magnify, i.e., zoom, the aperture diameter of the interference pattern, means to focus either the measured or limiting aperture onto the face of the vidicon, and means for transducing both the alignment spots and the interference pattern with a standard CCTV camera.

36 citations


Journal ArticleDOI
TL;DR: In this article, a broad-band approach to the detection of acoustic emission in which a capacitance transducer has been used to record the transient elastic waves generated by crack growth processes as surface displacements is described.
Abstract: Describes a new broad-band approach to the detection of acoustic emission in which a capacitance transducer has been used to record the transient elastic waves generated by crack growth processes as surface displacements. A unique specimen geometry, the 'Yobell' has been developed to reduce interference from internal reflections of the ultrasonic pulse, so that the measured surface displacements can be compared with those calculated for a source buried below the surface of the half-space. A static source model has been used to relate the rise-time and amplitude of transients to the time-scales and magnitudes of incremental crack growth.

31 citations


Journal ArticleDOI
TL;DR: Optimum performance of an interferometer in terms of highest and most uniform modulation efficiency for unpolarized radiation will be obtained by selecting the beam-splitter thickness to cover the wavenumber range of interest within the first interference lobe and by utilizing higher angles of incidence than the mechanically convenient 45 degrees.
Abstract: Absorption and complete multipath interference have been included in the calculation of the modulation efficiency of a far i.r. Michelson interferometer with 25-μm and 100-μm Mylar beam splitters over the range of wavenumbers between 20 cm−1 and 125 cm−1 for angles of incidence between 45° and 80°. These results show that optimum performance of an interferometer in terms of highest and most uniform modulation efficiency for unpolarized radiation will be obtained by selecting the beam-splitter thickness to cover the wavenumber range of interest within the first interference lobe and by utilizing higher angles of incidence than the mechanically convenient 45°. Practical constraints will usually limit this angle to a value somewhat less than the optimum of about 75° for Mylar beam splitters.

29 citations


Journal ArticleDOI
J. Byrne1
01 Sep 1978-Nature
TL;DR: In this article, the sign reversal of a spinor wave function subjected to a 2π rotation has been observed in the double beam interference experiment using unpolarized neutrons, when one beam traverses a magnetic field before recombination, and equivalent effects may be observed in interference phenomena associated with any two-state system and a realisable photon analogue is proposed.
Abstract: The fringe shift observed in Young's double beam interference experiment using unpolarised neutrons, when one beam traverses a magnetic field before recombination, has been interpreted as implying direct observation of the sign reversal of a spinor wave function subjected to a 2π rotation. This interpretation is unsatisfactory because for any fermion the relative rotation of the spins in the two beams and the interference pattern are mutually incompatible observables. This incompatibility does not arise in the case of bosons which possess a state of zero spin-component. Furthermore, equivalent ‘sign-reversal’ effects may be observed in interference phenomena associated with any two-state system and a realisable photon analogue is proposed.

22 citations


Journal ArticleDOI
TL;DR: A new species of laser Doppler velocimeter is presented based on wavelength detection with a two-beam interferometer based on Deltaphi, which creates a sensitivity of the interference to wavelength changes by means of a fast feedback system.
Abstract: A new species of laser Doppler velocimeter is presented based on wavelength detection with a two‐beam interferometer. A finite optical path difference, Δφ, of the interferometer creates a sensitivity of the interference to wavelength changes. By means of a fast feedback system, the phase, Δφ/λ is kept constant. Wavelength changes are immediately answered by changes of Δφ generated with a Pockels cell. The Pockels cell voltage represents a continuous signal proportional to the instantaneous velocity component of the scattering object. A time resolution of 1 μs or lower can be obtained. The field of applications includes velocity recordings in gas flows containing tracer particles as well as velocity recordings of moving surfaces. A number of experiments are described demonstrating the performance of the system.

22 citations


Book ChapterDOI
01 Jan 1978
TL;DR: In this article, transient gratings have been used for temperature diffusivity measurements and excitation of different types of sound waves, corresponding to the free carrier or exciton density.
Abstract: The optical properties (refractive index and coefficient of absorption) of matter become spatially modulated in the interference region of two intensive light waves. The resulting grating patterns have been observed in liquids and solids by diffraction (“forced light scattering”) of a probing beam or by self-diffraction. Thereby the spatial amplitude of the optical constants is measured with interferometric sensitivity. Permanent gratings by been investigated extensively for holographic applications. This paper emphazises transient gratings, methods for measurement of fast grating decay times, and excitation mechanisms. Thermal gratings, corresponding to a spatially periodic temperature distribution, have been applied for temperature diffusivity measurements and excitation of different types of sound waves. In semiconductors gratings have been produced corresponding to a spatial modulation of the free carrier or exciton density.

Journal ArticleDOI
TL;DR: In this article, the effect of spatial separation on interference effects in pitch memory was investigated, where subjects compared the pitches of two tones that were separated by a sequence of different tones.
Abstract: An experiment was conducted to investigate the effect of spatial separation on interference effects in pitch memory. Subjects compared the pitches of two tones that were separated by a sequence of ...

Journal ArticleDOI
TL;DR: A 20-cm clear aperture modified Twyman-Green interferometer is described, which measures phase with an AC technique called phase-lock interferometry while scanning the aperture with a dual galvanometer scanning system.
Abstract: A 20-cm clear aperture modified Twyman-Green interferometer is described. The system measures phase with an AC technique called phase-lock interferometry while scanning the aperture with a dual galvanometer scanning system. Position information and phase are stored in a minicomputer with disk storage. This information is manipulated with associated software, and the wavefront deformation due to a test component is graphically displayed in perspective and contour on a CRT terminal.

Patent
Carl A. Zanoni1
21 Apr 1978
TL;DR: In this paper, an electro-optical sensor is described which provides an output for precisely locating the centers of interference fringes in either a real-time interference pattern or an interferogram.
Abstract: An electro-optical sensor is described which provides an output for precisely locating the centers of interference fringes in either a real-time interference pattern or an interferogram. By scanning the fringe pattern either by moving the fringe pattern, by effectively moving the photoelectric sensor, or both, the centers of the fringes can be rapidly and precisely determined from the first derive of the output of the photodetector.

Journal ArticleDOI
TL;DR: In this paper, the use of a triangular cyclic interferometer for obtaining two counter-propagating optical beams which are accurately collinear is described, and its performance including the tolerance sensitivity is analyzed.
Abstract: The use of a triangular cyclic interferometer for obtaining two counter-propagating optical beams which are accurately collinear is described, and its performance including the tolerance sensitivity is analysed. A novel technique for facilitating fringe observation has led to the realisation of an instrument with a demonstrated angular alignment capability of 1 mu rad. The new design permits real-time monitoring of the interferometer. The whole alignment operation of the interferometer relies on visual observation of interference fringes.

Proceedings ArticleDOI
15 Dec 1978
TL;DR: An automatic interference pattern processor has been developed for the purpose of rapidly and accurately evaluating either real time interference patterns or interferograms to provide quick and easily interpretable feedback so that the operator can monitor the system's measurements.
Abstract: An automatic interference pattern processor has been developed for the purpose of rapidlyand accurately evaluating either real time interference patterns or interferograms. Thesystem has been designed to provide quick and easily interpretable feedback so that theoperator can monitor the system's measurements. The system includes: (1) a semi -automaticmode to facilitate the measurement of difficult interference patterns and (2) an integral,easily used calibration mode. The results of the least squares evaluation are availablein a variety of formats.IntroductionInterferometry has long been used in optical metrology. The advent of the laser has madeits use widespread not only among optical component and system fabricators but also amongthe users of optical components and systems.For most interferometry the output of the measurement is an interference fringe patternwhich can be observed in real time and photographed to produce an interferogram.. The typeof pattern is determined by the particular measurement configuration and by the errors inthe article under test. The quantitative evaluation of an interference fringe pattern isusually based on ascertaining the fractional deviation of the interference fringe patternfrom some ideal, best - fitting pattern. The denominator of the fractional deviation is themeasured spacing between a pair of fringes in the ideal pattern.The quantitative usefulness of an interference pattern is dependent upon having a methodof data extraction and evaluation. Interference pattern evaluation can range in complexityfrom a simple, subjective visual evaluation to an elaborate evaluation of the data extractedby an automatic microdensitometer with a large computer.1,2,3 In between these extremesthere are a great variety of means for hand evaluation.Unfortunately, the aforementioned techniques are either (1) subjective and, therefore, ofdubious accuracy, (2) extremely tedious and time consuming, or (3) require access to an ex-pensive, sophisticated facility. Therefore, for most users of interferometry, the diffi-culty in evaluating the output interference pattern has been a serious obstacle not only toits broader use but also to the achievement of its inherent accuracy and precision.This paper describes a new electronic instrument, an automatic pattern processor, whichhas been designed specifically to evaluate an interference pattern which has been trans -duced by a low geometric distortion CCTV camera. The system performs a least squares fitto an array of points located on the center of the fringes. The coordinates of the arrayof points located on the fringe centers are obtained either automatically or manually. Thesystem is essentially a video fringe center coordinate digitizer with the numerical computa-tion capability to do rapid, sophisticated analysis of the data. The system is an attemptto make available to most users of interferometry, an objective, powerful, and essentiallyreal -time interference pattern evaluation capability available previously only at a fewfacilities.Technical ConsiderationsGeneralThe fringes in an interference pattern represent contour levels of optical path dif-ference (OPD) between a reference wavefront and a measurement wavefront which has inter-acted with the article or system under test. The positions of the centers of these fringesare the basic raw data for evaluation of the interference pattern.For a numerical evaluation of the interference pattern, it is desirable to have as uni-form as practical a sampling of the interference pattern over the clear aperture (pupil).This is best achieved by using straight -line bias fringes. It is useful to use well-definedpatterns without closed fringes in order to eliminate ambiguity in numbering the fringes,i.e., assigning order numbers. Phase information is ascertained by specifying the locationof the zero order. This can be done either manually or automatically.

Patent
Richard Dr Ing Klemm1
24 Nov 1978
TL;DR: In this paper, the order of interference suppression and coherent integration is changed such that the echo values are first fed to a circuit to effect a Fourier transformation, and a sub-optimal detection method suitable for real-time operation is derived from the optimum detection model in that sub-matrices symmetrical with the principle diagonal are formed from the power spectrum matrix.
Abstract: Disturbing components of the Doppler frequency spectrum in a radar receiver, having coherent integration, are suppressed In this technique, the order of interference suppression and coherent integration is changed such that the echo values are first fed to a circuit to effect a Fourier transformation Then, the disturbing components in the frequency band are deliberately suppressed, and a sub-optimal detection method suitable for real-time operation is derived from the optimum detection model in that sub-matrices symmetrical with the principle diagonal are formed from the power spectrum matrix, through which approximate decorrelation of the disturbing components is achieved


Journal ArticleDOI
TL;DR: Tests of an instrument designed for Fourier transform spectroscopy in the 500-1000-microm spectral range are reported and shown to be in agreement with the analysis of the all-reflection Michelson interferometer.
Abstract: The beam splitter of the all-reflection Michelson interferometer consists of a combination of three parallel diffraction gratings. This paper extends the analysis of the instrument to include the effects of lateral errors in the grating adjustment (i.e., displacements parallel to the grating faces and perpendicular to the grooves). Such errors are shown to introduce a phase shift independent of wavenumber and proportional to grating order number. Tests of an instrument designed for Fourier transform spectroscopy in the 500–1000-μm spectral range are reported and shown to be in agreement with the analysis. For wavenumbers which pass through the instrument in 2 or more orders, cross-order interference effects are expected to occur which cause rapid variations in the efficiency vs wavenumber curve. This possibility should be eliminated in the design of a practical instrument. The resolution of the test instrument (1.6 cm−1) was insufficient to reveal this effect.

Patent
07 Sep 1978
TL;DR: In this paper, phase gradients of an interference pattern produced by optically heterodyning a returned glint from a remote target with a portion of the transmitted beam are used to assign conjugate corrective phase distortion values to COAT actuators.
Abstract: A high speed, two dimensional phase gradient map of atmosphere-induced phase gradients measures the distortion of an optical beam transmitted through the atmosphere. This is accomplished by detecting phase gradients of an interference pattern produced by optically heterodyning a returned glint from a remote target with a portion of the transmitted beam. The phase gradients are utilized to assign conjugate corrective phase distortion values to COAT actuators to alter the phase structure of the waves at the transmitter aperture. In one embodiment, two interference patterns are formed with one pattern phase shifted by 90° with respect to the other. The phase gradients and their direction are detected as a function of position across the transmitter aperture by the use of two optical scanners driven in synchronism to scan the respective interference patterns. An electrical phase shifter is used in one channel along with sum and differencing units and an up-down counter to detect both the amplitude and direction of the phase gradients. This information is used to position wavefront correcting mirrors in the transmitter aperture to cancel out atmospheric distortion by properly predistorting the transmitted beam.

Patent
15 Mar 1978
TL;DR: In this article, a receiving system for digital communication signals modulated on a carrier in the form of binary frequency modulation in a propagation medium which is affected by reflections in which the information losses occurring as a result of phase and amplitude distortions are automatically determined by two mutually supplemental arrangements.
Abstract: A receiving system for digital communication signals modulated on a carrier in the form of binary frequency modulation in a propagation medium which is affected by reflections in which the information losses occurring as a result of phase and amplitude distortions are automatically determined by two mutually supplemental arrangements. One of these arrangements includes in a first branch a frequency discriminator after which is connected a device for recognizing interference peaks caused by reflection distortions and further including a circuit which compensates for these interference peaks. The other arrangement contains an amplitude demodulator which is connected in parallel to the frequency demodulator in a second branch. The outputs of both branches are supplied to a switch which is controlled by an amplitude modulation evaluation device which at a recognizable amplitude modulation of sufficient magnitude connects the second branch to a common output, and at a recognizable frequency modulation connects the first branch to this output.

Proceedings ArticleDOI
01 Jan 1978
TL;DR: In this article, interference effects between large cylinders in waves are described and a prediction method that reduces computer costs by a factor of several hundred when faced with the specific problem of two neighboring circular cylinders, rather than bodies of arbitrary geometry.
Abstract: This paper describes interference effects between large cylinders in waves. Reliable predictions of wave-induced forces on large offshore structures are important from technical and economic standpoints. This paper offers a prediction method that reduces computer costs by a factor of several hundred when faced with the specific problem of two neighboring circular cylinders, rather than bodies of arbitrary geometry. Theoretical predictions were confirmed by experiments in a model wave basin.

Journal ArticleDOI
TL;DR: In this article, a filamentary spatial filter is placed on the diffraction plane of a double-diffraction optical system, and a small phase object is placed in the object plane of the system.
Abstract: A new type of interferometer is developed by putting a filamentary spatial filter on the diffraction plane of a double-diffraction optical system. A small phase object is placed in the object plane of the system. The light passing through the uniform region around the phase object is scattered by the filter. This scattered light interferes with the light passing through the phase object in the image plane; a common path interferometer is constructed. In order to obtain good visibility of the interference fringes in the image plane, optimum conditions are discussed from scalar diffraction theory and are confirmed experimentally. By displacing the filter along the optical axis, we can change the phase difference between object and scattered light. Therefore, the phase acceleration or retardation at a point in the object can be precisely determined by analysing the intensity change at the conjugate point in the image plane during the displacement of the filter. Experimental results show that the error in suc...

Journal ArticleDOI
TL;DR: In this article, an interference acoustical method for measuring velocity, attenuation and reflection of acoustic surface waves was developed for diagnostics and nondestructive testing of acoustic wave devices.
Abstract: An interference acoustical method for measuring velocity, attenuation and reflection of acoustic surface waves was developed. Applications to diagnostics and nondestructive testing of acoustic surface wave devices are discussed.


Patent
06 Jul 1978
TL;DR: In this article, a system for frequency selective location of electromagnetic high frequency oscillations w.r.t. azimuth and elevation has been proposed for extraction of as much information as possible from incident waves, determining when waves arrive simultaneously and cause interference effects.
Abstract: A system for frequency selective location of electromagnetic high frequency oscillations w.r.t. azimuth and elevation has a number of antennas and associated receivers whose output signals are processed. The system is designed for extraction of as much information as possible from incident waves, determining when waves arrive simultaneously and cause interference effects. It determines also the field strength, azimuth and elevation of each incident wave. A network of automatic field strength sensors which scan the complex field strength is distributed regularly or statistically over an area large in comparison with the received wavelength. The sensor high frequency signals are evaluated as to magnitude and phase with reference to the corresp. sensor positions in a central processor.

27 Mar 1978
TL;DR: In this article, a phase detection and timing algorithm, using a priori known dispersion characteristics, is demonstrated to time the onset of simulated teleseismic long-period surface waves within 30 seconds accuracy in 70% of the tested cases.
Abstract: : The feasibility is evaluated of applying instantaneous amplitude, phase and frequency measurements to automatically detect, time and identify seismic events. Detection based on phase measurements is shown to be in principle 6 dB more sensitive than detection based on amplitude measurements. A phase detection and timing algorithm, using a priori known dispersion characteristics, is demonstrated to time the onset of simulated teleseismic long-period surface waves within 30 seconds accuracy in 70% of the tested cases, for waveforms down to 0 dB signal-to-noise ratio. By phase measurement, rather than by amplitude measurement, this algorithm also provides a measure of the surface wave signal-to-noise ratio. These results can be applied in the extraction of weak surface waves. Phase detection of teleseismic short-period bodywaves was not found to be feasible, due to the interference of early- arriving secondary signals. Therefore, short-period P-wave detection and timing are performed essentially by envelope peak detection; instantaneous frequency measurements are also used in the timing process. Measurements of the instantaneous frequency permit analysis of the delay times of secondary signals partially overlapping with earlier primary signals, down to the primary signal detection level.

Journal ArticleDOI
TL;DR: In this paper, the centroid shift method was applied to lifetime measurements using a pulsed beam and a time-centroid spectrum and a mean-life spectrum were created automatically with a minimum of human interference.

Journal ArticleDOI
TL;DR: In this paper, two crystal component interferometers utilizing double-Laue-case diffraction have been constructed and interference finges are observed by inserting aluminum sheets of various thicknesses as phase shifting material.
Abstract: Two crystal component interferometer utilizing double-Laue-case diffraction has been constructed. Interference finges are observed by inserting aluminum sheets of various thicknesses as phase shifting material. The intensities of the forward beam ( O -beam) and the deviated beam ( H -beam) oscillate complementarily with the thickness of aluminum.

01 Jun 1978
TL;DR: In this paper, the first-order statistical probability densities (PDFs) and associated exceedance probabilities (PDs or APDs) are obtained for the instantaneous amplitudes (X), and instantaneous magnitudes, |X|, of Class B noise.
Abstract: This report is the third in a continuing series devoted to the development of analytically tractable, statistical-physical models of man-made and natural electromagnetic interference. Here, the first-order statistical probability densities (PDFs) and the associated exceedance probabilities (PDs or APDs) are obtained for the instantaneous amplitudes (X), and instantaneous magnitudes, |X|, of Class B noise. There are needed not only for experimental studies but, also, particularly for the analysis and evaluation of the performance of optimum and suboptimum receivers in Class B interference environments.