Showing papers on "Interference (wave propagation) published in 1968"

The physics of vibrations and waves

Abstract: Introduction to First Edition. Introduction to Second Edition. Introduction to Third Edition. Introduction to Fourth Edition. Introduction to Fifth Edition. Introduction to Sixth Edition. 1 Simple Harmonic Motion. 2 Damped Simple Harmonic Motion. 3 The Forced Oscillator. 4 Coupled Oscillations. 5 Transverse Wave Motion. 6 Longitudinal Waves. 7 Waves on Transmission Lines. 8 Electromagnetic Waves. 9 Waves in More than One Dimension. 10 Fourier Methods. 11 Waves in Optical Systems. 12 Interference and Diffraction. 13 Wave Mechanics. 14 Non-linear Oscillations and Chaos. 15 Non-linear Waves, Shocks and Solitons. Appendix 1: Normal Modes, Phase Space and Statistical Physics. Appendix 2: Kirchhoff's Integral Theorem. Appendix 3: Non-Linear Schro..dinger Equation. Index.

Further Experiments on Interference of Independent Photon Beams at Low Light Levels

Abstract: Interference fringes produced by the superposition of light beams from two independent lasers have been investigated under conditions where the light flux was so low that one photon was usually received at the detector before the next one was emitted by one or the other source. Because the average number of photons detected in each observation was only about 10, a photon correlation technique was used to demonstrate the presence of interference fringes. The measurement procedure was automated, and this led to much greater statistical accuracy than was previously reported. The effect of varying the observation time and the number of interference fringes sampled was investigated, and found to be in good agreement with theory.

Light modulator by gated interferometry

Abstract: A light modulator employing a Michaelson interferometer in which an incident beam is divided and recombined producing interference fringes in space. The light output may be selectively modified by providing a gate or mask at the output, and by electrically changing the optical path length of one leg. This can be accomplished through the Kerr or Pockels effect. In a modifications, Faraday rotation is employed to destroy the interference between two coherent beams.

Frequency control for tunable laser utilized in a position control system

Abstract: A CALIBRATION SYSTEM FOR A TUNABLE LASER UTILIZED AS A POSITION INDICATING DEVICE IN A POSITION CONTROL SYSTEM INCLUDES AN INTERFEROMETER COUNTING THE INTERFERENCE FRINGES IN A PATTERN PRODUCED BY THE LASER OUTPUT AND A PORTION OF THE OUTPUT RETURNED FROM A PRISM DISPOSED ON A CARRIAGE WHICH IS MOVED THROUGH A PRECISELY KNOWN, REPEATABLE MOVEMENT. BY USING THE INTERFEROMETER OUTPUT TO COUNT DOWN A DIGITAL COUNTER INTO WHICH A NUMBER HAS BEEN PRESET WHICH CORRESPONDS TO THE CHANGE IN THE NUMBER OF FRINGES THAT SHOULD BE OBSERVED AT A GIVEN LASER FREQUENCY, ANY REMAINING COUNT AFTER THE MOVEMENT INDICATES ERROR DUE TO CHANGES IN TRANSMISSION CHARACTERISTICS OF THE BEAM PATH. THE REMAINING COUNT MAY THEN BE USED TO PROVIDE AN ANALOG VOLTAGE FOR ADJUSTMENT OF THE LASER FREQUENCY.

Laser frequency stabilization system and method

Abstract: A method of stabilizing the operating frequency of a laser which includes comparing by means of interference the relative phase of two beams of radiant energy from the laser, one of which is a reference while the other passes through the active lasing material The optical path traversed by the reference beam is adjusted to produce a selected condition at the point of interference when the laser is oscillating at a frequency which corresponds exactly to an anomaly in the dispersion of the lasing material Thereafter, the laser frequency is stabilized by adjusting its operating frequency to maintain this condition Preferably, the comparison is made by varying the reference phase about the selected value Apparatus for performing this method includes means defining two substantially equal optical paths for radiation emitted by the laser, one of which extends through the active material of the laser The two paths are terminated at the same point so that interference occurs and the apparatus includes means for detecting the output from the point of interference Finally, means are provided for controlling the laser frequency to maintain a predetermined interference condition

Coherent optical adaptive techniques.

Abstract: : A system was designed, constructed and tested which provides dynamic adaptive phase compensation for atmospheric distortions. This demonstrates that arrays can be built larger than previously thought possible because of atmospheric effects. Without adaptive controls, the atmosphere limits the signal-to-noise ratio improvement and the beamwidth reduction which can be obtained using a larger transmit-receive aperture. We accomplished phase compensation for the transmitted beams and the received signals of a two-element 10.6 micron array. By providing adaptive phase control to assure that the two transmitted beams arrived at the target in phase, the power on target was increased by at least 75 percent over the nonadapted case. In addition, the amplitude fluctuations of the received signals were drastically reduced because the adaptive transmitting system eliminated the frequent destructive interference normally seen when two beams are transmitted. Adaptive control of the relative phase of the two received signals before adding also resulted in comparable increases in signal power. The locking of two lasers with a 4.5 MHz difference frequency provided the local oscillator for heterodyne detection. A near target 500 feet and a far target 3 miles from the transmitter were used. (Author)

Static sampling distance relays

Abstract: A sampling technique has been developed which allows a comparison of instantaneous values derived at different instants of time, thereby dispensing with the need to phase-shift or mix signals derived from the primary line quantities. Both amplitude and phase comparisons are used to derive a variety of impedance characteristics. The relays combine high sensitivity with a high resistance to interference. Detailed results are presented for a current-polarised relay with a characteristic surrounding the probable fault area.

Transmission Fringes in Reflection Multiple-Beam Interferometry

Abstract: Transmission fringes in reflection multiple-beam interferometry are obtained independently of the characteristics of the coating of the reference surface by coupling a two-beam interferometer to the multiple-beam interferometer.The two-beam interferometer is defined by the reference surface of the multiple-beam interferometer and one additional mirror in a Twyman configuration.

An interference method for determining the degree of parallelism of (laser) surfaces.

Abstract: A method for measuring the angle between two nearly parallel surfaces is presented. Convenient to use, the method has ample brightness and sensitivity for use in aligning the various surfaces often found in laser cavities. A cw laser is focused to provide a point source of light which illuminates the two surfaces in question. The reflected light beams form an interference pattern from which the angle between the surfaces can be easily measured. A simple equation is given relating the fringe position to angular separation.

The use of a null-point method to study the acquisition ok simple and complex transformation skills

Abstract: A null-point experimental method for measuring human performance is described. This method can be used in studies of learning and in other situations where the effect of learning is appreciable, though irrelevant to the experimenter's objective. It provides a form of constancy of experimental conditions which is appropriate if the subject is conceived as an imperfect goal-directed system. The method is exhibited in connexion with two experiments and a subsidiary study. One experiment involves the acquisition of a skill in which the human subject learns to apply a single transformation rule. For the other main experiment, the subject learns to deal alternately with two rules (so chosen that interference as well as positive transfer of training takes place). Further, in this case, the subject learns a concept which (in an operational sense) comprehends the pair of rules. The subsidiary experiment involves a modification of the original technique which may be useful in more detailed investigations of concept learning.

Methods and apparatus for producing a holographic light pattern from an ultrasonic impulse

Abstract: A method and apparatus employing an ultrasonic signal to cause an interference pattern between a coherent light reference beam and a second coherent light beam which is ultrasonographically modulated to form recordable interference patterns in the form of a hologram.

Receiver for detecting and analyzing amplitude or angle modulated waves in the presence of interference

Abstract: This receiver includes in its IF channel a summing network by means of wh the output of a calibrated reference oscillator may be added to the received signals The frequency and amplitude of the reference oscillator are adjusted to match those of a desired one of several co-channel signals which may be simultaneously present in the IF channel The combined signals are amplitude limited and applied to a frequency deviation detector in which the wide frequency deviations caused by the interaction of the reference and desired signal are detected The technique can be used to demodulate angle or amplitude modulated signals obscured by jamming signals and to measure the frequency and amplitude of signals which are similarly obscured

Validity of the interference model for $$\pi \mathcal{N}$$ scattering

Abstract: It is shown in an extensive analysis of the\(\pi \mathcal{N}\) scattering data between 2 and 6 GeV/c that the interference model does not account correctly for some features of the data. Therefore some modifications of the model would be needed, if it is further applied to analyse all the forward and backward data in the intermediate energy region.

Automatic Interferometer with Digital Readout for Refractometric Analysis

Abstract: The paper describes an interference refractometer for liquids and gases which operates automatically and reads out in digital or analog form. A compensating technique using white light is used for measurement. Zero adjustment is achieved by rotating the compensator and capturing the zero-order white light fringe by photoelectric means. Measurement of the path difference compensated by the compensator is based on electronic interpolation and counting of interference fringes by optointerferometric means, a time division multiplex technique with pulse amplitude modulation being used to obtain the electrical fringe signals.

Absorptive Lines as RFI Filters

Abstract: A new class of ?distributed constant? filters has been recently developed using the normal propagation path of the electrical current in a wire, a cable, or a line to suppress interference. The three basic characteristics are the following: 1) Instead of using lumped reactive components (inductors, capacitors) connected to the wire, one superposes the suppressive effect to the normal straight and flexible conductor without any additional components. 2) The problem of mismatch at the interfaces with the generator and with the load (for example, a classical ? filter connected to a reactive load) is nonexistent, because the suppression is due to an absorption of the critical frequency components. The Q factor of such a line is substantially equal or less than unity in the frequency range considered. 3) In the case of nonsheathed cables (general case), if the suppression of the conducted interference is sufficiently high along the line (for example, a 20-dB attenuation is obtained for a linelength equal to a tenth of the wavelength at the considered frequency), radiation and induction of parasitic frequencies is automatically suppressed. The necessary absorption can be introduced on the cable or the line by using separately or together three different physical effects: 1) Absorption due to magnetic and dielectric losses. These losses are achieved by the use of special products, like magnetic ferrites with high Fe and Zn content, semiconductive and ferroelectric dielectrics, and with bulk or synthesized dispersive effects.

A measuring interferometer for high accuracy alignment.

Abstract: An interferometer is described that is capable of measuring the deviation of a target device from a plane with an accuracy of 0.1 micro, when the interferometer-target separation is as much as 10 m. This interferometer resembles one described in 1965 by Baldwin and Whitten in that they both use a Kosters prism and a Porro prism. The present use of a laser for the light source yields nonlocalized fringes at the output that are easily monitored by an electronic fringe detector.

Effect of Surface Errors and Misalignment of End Mirrors on the Photometric-Setting Accuracy of the Double-Passed Michelson Interferometer

Abstract: The effect on photometric-setting accuracy of mechanical misalignments and surface errors of the end mirrors of a double-passed Michelson interferometer has been analyzed. Tolerance limits are given for the mirror quality and their misalignments.

Interference of Sub-millimetre Waves over 450 m Path Difference

Abstract: SUB-MILLIMETRE waves are attractive for metrology over long distances, because they are not much scattered by fog or cloud1 and can be specularly reflected from ordinary machined surfaces. A device using interference over a long path difference would give a simple method of measuring small movements of a distant body and could be developed for the precise measurement of distances. Interference between beams which have traversed a large path difference requires that the radiation be confined to a narrow bandwidth, and to this end we were interested in finding the effective line width of the continuous-wave 337µ maser2. A preliminary experiment was carried out by beating two masers together as shown in Fig. 1, using a Putley indium-antimonide detector3 as the nonlinear mixing element.

Instantaneous fourier frequency analyzer using an interferometer

Abstract: INSTANTANEOUS FOURIER ANALYSIS OF THE FREQUENCY COMPONENTS IN A SIGNAL IS PERFORMED BY MEANS OF THE ANALYSIS OF THE PATTERN OF INTERFERENCE FRINGES PRODUCED BY TWO COHERENT LIGHT BEAMS, WHICH ARE INTENSITY MODULATED IN ACCORDANCE WITH THE SIGNAL AND WHICH ARE PROVIDED WITH A SYSTEMATICALLY VARIED PHASE DIFFERENCE BETWEEN INTERFERING RAYS IN THE BEAMS. THE PHASE DIFFERENCE IS VARIED IN ACCORDANCE WITH A LINEAR FUNCTION OF THE ALGEBRAIC PRODUCT OF TIME AND ANY FUNCTION OF DISTANCE FROM A POINT IN THE INTERFERENCE PATTERN WHERE THE PHASE DIFFERENCE IS ALWAYS EQUAL TO ZERO. IN ONE EMBODIMENT, THIS TYPE OF VARYING PHASE IS OBTAINED BY APPLYING A SAW-TOOTH TIME VARYING ELECTRIC VOLTAGE ACROSS A PAIR OF COMPOUND PRISMS, MADE OF ELECTRO-OPTIC MATERIAL IN PART, UPON WHICH THE BEAMS ARE INCIDENT IN EACH ARM OF A MICHELSON INTERFEROMETER ARRANGEMENT, THEREBY DEFLECTING THE BEAMS THROUGH AN ANGLE WHICH IS LINEARLY PROPORTIONAL TO THE TIME AFTER EACH SAW-TOOTH HAS COMMENCED. OBSERVABLE CHANGES IN THE PATTERN OF INTERFERENCE FRINGES OCCUR WHEN THE LIGHT INTENSITY IS THUS MODULATED IN ACCORDANCE WITH THE SIGNAL, AS COMPARED WITH NO SUCH MODULATION, AND THESE CHANGES OCCUR ONLY AT POSITIONS IN THE INTERFERENCE PATTERN DETERMINED BY THE RESPECTIVE FREQUENCY COMPONENTS IN THE SIGNAL.

An autocorrelation approach to the Brown Twiss interferometer

Abstract: A question that often arises about the principles underlying the Brown-Twiss stellar interferometer is "HOW can interference phenomena occur with light produced by incoherent sources?" Starting from the familiar interference pattern produced by two coherent sources, one can proceed in simple steps to a picture of two incoherent sources producing an interference pattern that moves about at random. This randomly moving pattern leaves behind a "footprint" in the form of the intensity autocorrelation function. This report describes how the autocorrelation function for an extended, incoherent source may be constructed. It is this function that is measured by the Brown-Twiss stellar interferometer.

Measurement of Manmade Electromagnetic Radiations from a 200-Mile Orbit

Abstract: The study determined the feasibility of measuring electromagnetic radiations over the 0.1 to 15 GHz frequency range from a orbiting spacecraft. The primary objective was to define an experiment for an Apollo mission, although an unmanned space vehicle experiment is also considered. The study concludes that such an experiment is feasible and suggests an evolutionary series of experiments. Significant objectives of the first experiment are: (1) to measure RF as a function of earth location with -100 dbm receiver sensitivity, (2) enhance the over-all experiment with the astronaut by making decisions and performing real-time analysis of the experiment and of intentionally varied signals, (3) the experiment can be integrated into a mission depending on the spacecraft and other experiments, (4) extensive coverage of populated areas by orbit inclinations of 28 to 90 degrees, and (5) process and display of accumulated data by computers to the extent required by different users. The resulting data may find use in frequency allocation, equipment specifications, operational procedures, and interference maps that will be useful in site selection.

Multiple display of interferograms.

Abstract: Interferometric investigations have been simplified considerably by the application of holographic procedures. The incoherent superposition of holograms, known as the double exposure technique, has eliminated the need for interferometric quality optical components, and a three-beam holographic method has been proposed that avoids using two exposures when cancellation of system defects is not required. The purpose of this note is to bring attention to the possibility for displaying different types of interferograms simultaneously side by side by combining the double exposure method with either the three-beam or the incoherent spatial frequency multiplexing technique.

Effects of Interference on Bottom‐Bounce Propagation of Low‐Frequency Sound in Deep Water

Abstract: A model of surface‐to‐surface bottom‐bounce propagation is described as a summation of plane waves at the receiving hydrophone. The model shows that variations in propagation loss with range consist of long period variations produced by the dipole effect at the source and at the receiver, and faster variations resulting from the interference of two or more bottom bounce arrivals. Theoretical variations derived from the model are compared with the results of propagation experiments for the range interval 0–80 kyd carried out in deep water using hydrophones at depths of 80 and 400 ft and a 230‐Hz CW projector as a sound source. The model parameters were based on the significant propagation paths determined by measurements made with explosive charges during the same experiment. The experimental results agreed in general with those derived from the model but also displayed a random component, the magnitude of which varied with the trial site.