Showing papers on "Interference (wave propagation) published in 1980"

Rough surface interferometry at 10.6 µm

Abstract: An IR Twyman-Green interferometer is described. It uses a cw CO2 laser as a light source operating at a 10.6-μm wavelength. Theoretical analysis and experimental measurements of the relationship between the contrast of the interference fringes and the rms roughness of test surfaces are discussed. Interferometric testing results and special alignment methods are shown for rough surface optics.

Automatic gain control system

Abstract: An automatic gain control for a receiver includes a gain controller for controlling the gain of the receiver, a control device connected to the tuning device of the receiver for varying and controlling the tuning frequency of the tuning device, and a level detector connected to the control device and the receiving signal system of the receiver for detecting the receiving level. The control device includes a calculation processor connected to the tuning device, the level detector and the gain controller, and the calculation processor includes a detector for detecting the absence or presence of other broadcasting waves (interference waves) in a predetermined relation with the receiving frequency of the receiver and for controlling the gain controller in such a manner as to reduce the gain thereof when the signal intensity of the interference broadcasting waves exceeds a predetermined level predetermined by the level detector.

A residual intersymbol interference error bound for truncated-state Viterbi detectors

Abstract: The Viterbi algorithm has been proposed for the symbol-by-symbol detection of discrete pulse amplitude modulated signals transmitted over noisy time-dispersive channels. The resulting detector has considerable complexity, requiring the storage of 2^{m} state variables for binary signaling. A truncated-state detector assumes the channel memory m is much less than it really is and as such neglects some of the channel's intersymbol interference. An upper bound is prescribed for the detector's bit error probability due to this neglected interference in the case of binary signaling. This interference degrades the detector's performance in the same functional manner that intersymbol interference degrades the performance of the standard quantizing detector. This degradation can be considerably reduced for troublesome channels by optimally choosing the state variables for truncated-state detection.

Infrared surface wave interferometry

Abstract: An interference phenomena is described which involves infrared surface electromagnetic waves on coated metals. The interference is demonstrated with a two‐beam surface wave interferometer of variable path length which utilizes the strong coupling between surface and bulk electromagnetic waves at coating edges.

Hybrid adaptive sidelobe canceling system

Abstract: A system for adjusting the sidelobe response of a main antenna is disclosed. This iterative process results permits the sidelobe canceling in sequential step reduction in interference thereby greatly reducing the time required to respond to changes in the characteristics of the interference. The response of the phased array is adjusted by combining the composite signal from the main antenna with signals from auxiliary channels which have an adjustable phase and amplitude. The desired amplitude and phase of the auxiliary channels is determined using an iterative mathematical process which emphasizes the most recent data. Emphasizing the most recent data permits the system to be used in the scanning mode or to reduce interference from moving sources.

Chapter vii – elements of the theory of interference and interferometers

Abstract: Introduction IN Chapter III a geometrical model of the propagation of light was derived from the basic equations of electromagnetic theory, and it was shown that, with certain approximations, variations of intensity in a beam of light can be described in terms of changes in the cross-sectional area of a tube of rays. When two or more light beams are superposed, the distribution of intensity can no longer in general be described in such a simple manner. Thus if light from a source is divided by suitable apparatus into two beams which are then superposed, the intensity in the region of superposition is found to vary from point to point between maxima which exceed the sum of the intensities in the beams, and minima which may be zero. This phenomenon is called interference. We shall see shortly that the superposition of beams of strictly monochromatic light always gives rise to interference. However, light produced by a real physical source is never strictly monochromatic but, as we learn from atomistic theory, the amplitude and phase undergo irregular fluctuations much too rapid for the eye or an ordinary physical detector to follow. If the two beams originate in the same source, the fluctuations in the two beams are in general correlated, and the beams are said to be completely or partially coherent depending on whether the correlation is complete or partial. In beams from different sources, the fluctuations are completely uncorre-lated, and the beams are said to be mutually incoherent. When such beams from different sources are superposed, no interference is observed under ordinary experimental conditions, the total intensity being everywhere the sum of the intensities of the individual beams.

An Adaptive Antenna for Rejection of Wideband Interference

Abstract: A modification to the adaptive array under the directional constraint [1] is proposed to improve its performance of rejecting wideband interference. By analogy to the pattern synthesis of an antenna array which produces a flat null in its radiation pattern, an additional quantity that corresponds to the derivative of the pattern is generated and combined with the standard feedback quantity to control the weights of the array. This composite system is tested by computer simulation experiments and the following points are demonstrated in contrast to the conventional, simple system: 1) faster adaptation against wideband interference, 2) remarkable improvement of the signal-to-noise ratio of the output, i. e., very small fluctuation.

Scanning Fabry-Perot interferometer: performance and optimum use in the far infrared range

Abstract: A compact scanning Fabry-Perot interferometer using metallic meshes as reflectors is described. Its performance characteristics such as finesse, transmission, and resolution are measured as functions of the interference order for several wavelengths in the 100–400-μm range. The good agreement found between theory and experiment leads to a set of curves from which the effective finesse of the instrument and its optimum use, for a fixed far infrared wavelength and given meshes, can be predicted. It is found that the effect of the incident light cone angle is more important than that of surface defects of parallelism of the meshes and that it limits the maximum resolution.

Method and device for the measurement of the phase shift of the waves in a ring interferometer

Abstract: 1. A method of measuring the phase difference of electromagnetic waves circulating in opposite sense in a ring interferometer, comprising the step of generating an electromagnetic wave, separating this electromagnetic wave into two phase components which are fed into the end of the ring in order to generate the waves ciculating in opposite sense, modulating the phases of the two waves in periodical and reciprocal manner, recombining the two waves at the ends of the ring and detecting the recombined waves, characterized in that in the modulating step the phase of the two waves circulating in opposite sense are modulated at least at one end of the ring according to a function satisfying the relation PHI(t)=PHI(t+2 tau), wherein tau is the time necessary for each wave for passing through the optical way provided by the ring, and at that the step of detecting the phase difference between the two recombined waves is carried outs by measuring, at the frequency (1/2 tau) or at an entire multiple (k) of this frequency the optical power of the component of the recombined waves proportional to the sine of the phase difference between the waves.

Dual surface interferometer

Abstract: A double-pass interferometer is provided which allows direct measurement of relative displacement between opposed surfaces. A conventional plane mirror interferometer may be modified by replacing the beam-measuring path cube-corner reflector with an additional quarter-wave plate. The beam path is altered to extend to an opposed plane mirrored surface and the reflected beam is placed in interference with a retained reference beam split from dual-beam source and retroreflected by a reference cube-corner reflector mounted stationary with the interferometer housing. This permits direct measurement of opposed mirror surfaces by laser interferometry while doubling the resolution as with a conventional double-pass plane mirror laser interferometer system.

Location of the interference structure near the lower oblique (whistler) resonance cone

Abstract: By numerically solving the dispersion relation for electrostatic waves in a Maxwellian magnetoplasma with stationary ions, it is shown that above a certain frequency fα the interference structure may be either inside or outside the resonance cone, depending on the distance from the source.

Length Measurement of Gauge Blocks Using a 3.39 µm He-Ne Laser Interferometer

Abstract: An infrared interferometer is described for length measurement which uses a simply stabilized 3.39 µm He-Ne laser as a light source and has a piezoelectric-transducer scanning system for recording interference fringes of two fields of view simultaneously and automatically. Pointing accuracy of the order of interference obtained is estimated to be 0.5° in phase. Using this interferometer, the refractive index of air at a wavelength of 3.39 µm is measured with an accuracy of 3×10-8 and Edlen's dispersion formula is confirmed with an accuracy of less than one part in 107. The length of a gauge block of nominal length 200 mm is measured with an accuracy of 5×10-8 in standard deviation.

Autocorrelation method for measuring the transfer function of optical systems.

Abstract: An unconventional autocorrelation method is described for measuring the transfer function of optical systems. The interference takes place between the scattered waves obtained from two laterally sheared correlated partial diffusers. The output of a detector responding only to an extremely narrowband of spatial frequencies is proportional to the autocorrelation of the system pupil function. An automatic display of the transfer function is obtained by continuously varying the shear between the diffusers. We present the theory and some experimental results of this simple and inexpensive device. A study of various parameters affecting the performance of the instrument is also given.

Short-range doppler radar

Abstract: In a Doppler radar system for measuring the velocity of a vehicle, such as an automobile, in order to lessen interference with external electric wave appliances, such as radios and televisions, caused by transmitting microwaves, one of the higher harmonics generated from a mixer diode driven by the fundamental waves of a local oscillator is selected by a filter for transmission and is used as the transmission output wave, whereby the power of the transmission waves is remarkably reduced in comparison with the mixer driving power.

Wide band demodulator of phase modulated signals

Abstract: A wide band demodulator of phase modulated radio frequency signals is disclosed, wherein first and second sets of sonic waves are generated within a Bragg cell, one set being phase shifted with respect to the other set, together with means for directing a linear diffraction pattern of the light output of the Bragg cell at first and second phase displaced correlation masks, together with a first and second array of photodetectors which receive the integral of the light passing through associated masks, thereby to enable the simultaneous detection of a very large number of phase modulated signals on a real time basis, and wherein there is virtually no interference between channels and the need for a very large number of local oscillators is eliminated.

Lateral shear interferometer using twin three-beam holograms.

Abstract: A lateral shear interferometer using twin three-beam holograms is described. In the interferometer two first-order diffracted light beams from the first hologram play the role of a beam splitter; the second hologram eliminates the effect of tilt. This interferometer has two advantages over the single three-beam hologram lateral shear interferometer: (1) it can be used for small f/No. lens tests; (2) any small aberration of the optical system of the interferometer can be canceled by using the second hologram. In this paper, shearing interferograms of lens aberration, of refractive indices around a flame, and of spouting gas are demonstrated.

Pressure sensitive fibre=optic sensor e.g. hydrophone - has reacting fibre in series with optical delay line with light source coupled to one end of light path

Abstract: The sensor has a light path formed by a pressure-sensitive optical fibre (25) in series with at least one optical delay line (26). A light source (11) is coupled to one end of the light path with the propagation times for the light through the pressure-sensitive optical fibre (25) and the optical delay line (26) being equal. Pref. the light source (11) comprises a semiconductor laser, which is coupled to a beam splitter (20), with two inputs and outputs (21...24), two of which are coupled via the optical path, the remaining output being coupled to a photodetector (17). The light is pref. transmitted in both directions along the optical path to set up interference in the beam splitter with the photodetector (17) monitoring variations in this interference. The sensor can be used as a fibre-optic hydrophone.

On the interference between overlapping autoionisation lines

Abstract: The conditions under which interference effects may appear in the decay spectrum of coherently excited overlapping initial states are considered. It is demonstrated that interference effects are excluded under such experimental conditions as those reported in a recent study of the autoionisation spectrum of sodium.

Computer synthesis of optical interference figures

Abstract: The interference figures produced by anisotropic crystals under the petrographic microscope can be synthesized by a digital model. This model allows the evaluation of a body of optical crystallographic theory as applied to interference figure phenomena. The accuracy and clarity of the figures produced by the digital model suggest applications for petrographers.

Transfer function with quadratic detection: coherent illumination

Abstract: The visibility of the interference terms over the image irradiance of a complex amplitude object immersed in a uniform background is described by an interference transfer function (ITF). It is shown that the ITF is the linear transfer function for coherent optical systems with quadratic detection when the test object either has low contrast or is periodic.

Folded-wave interferometer for laser-matter interaction studies.

Abstract: A folded-wave interferometer that allows for independent adjustment of the background fringe separation of two output interferograms is described. This white-light wide-angle instrument, based on the Michelson interferometer, has a large field of view limited only by the imaging optics.

Neutron total cross section of sulfur: Single level to multilevel to optical model

Abstract: This paper is a further analysis of the high resolution total cross section of sulfur for 25--1100 keV neutrons that previously were measured by Halperin, Johnson, Winters, and Macklin and evaluated by single-level analysis. The usual procedure in reporting the results of high resolution neutron cross sections has been to present the data and resonance parameters with corresponding neutron strength functions resulting from some type of R-matrix analysis. Often the important nonresonant phase shifts are not reported. In this paper, making use of both strength functions and phase shifts, we extend the analysis to include an average nuclear potential (a spherical optical model). An optical model analysis not only facilitates comparison with a broad spectrum of other nucleon-nucleus experiments, but also may provide an incentive for microstructure calculations. Six average empirical functions, two each for s/sub 1/2/, p/sub 1/2/, and p/sub 3/2/ partial waves, are derived from the R-matrix analysis. From these we deduce optical model parameters, the real and imaginary well depths for s- and p-wave neutrons, and the spin-orbit well depth for p waves. The resulting real well is deeper for p waves than for s waves and for averages over partial waves at higher energies. The depthmore » of the imaginary wells are about half those deduced at higher energies. An interesting feature of the analysis is that the multilevel curve including interference effects is produced from single-level parameters including the phase shifts.« less

Saddle-point approximation for M-ary phase-shift keying with adjacent satellite interference

Abstract: As the geosynchronous orbit for satellite communication becomes increasingly crowded, the effect of adjacent satellite interference is of primary concern. We describe here the saddle-point approximation technique for evaluating the error probability of M-ary PSK systems with adjacent satellite interference. In comparison with previous methods, this technique has the advantages of both computational simplicity and accuracy. Results include a sample calculation to study the effect of fading on the uplink of a 12/14-GHz quadraphase-shift-keying system with 3-degree satellite spacing and 3-m earth stations.

Power optimization in adaptive arrays: A technique for interference protection

Abstract: A weight control algorithm that may be used in a two-element adaptive array to protect a desired signal from an interference signal is described. The algorithm is a constrained gradient technique that either maximizes or minimizes array output power. It is shown that by choosing appropriately between minimization and maximization, a useful desired signal-to-interference-plus-noise ratio can be maintained at the array output over a wide range of signal powers.

Effects of interference between one- and two-photon processes

Abstract: Solutions are given for interaction between a three-level system and three arbitrarily intense fields, one of which has the sum frequency of the other two field frequencies. The results of a nonperturbative analytic treatment of the three-level Schr\"odinger equation are described. We find that the time dependence of the occupation probabilities of the three levels is strongly modified by the effects of interference between one- and two-photon processes.

Information recordinggreproducing method

Abstract: PURPOSE:To reduce the fluctuations in the angle of inclination of interference fringes and obtain good quality reproduced information by so radiating a hologram that spherical object waves and spherical waves for reference have a nearly equal angle of inclination with respect to the normal of the hologram disc. CONSTITUTION:Laser beam from a light source 8 is focused at the point S' by collimator lenses 9a, 9b, condenser lens 10, after which it is diverged as spherical waves for reference. Laser beam from a light source 3 is focused at the point S, after which it is diverged as object spherical waves. The optical axis B5 and B2 of both waves have the same angle of inclination with respect to the normal N1 of the surface of a hologram disc 1. Similarly the optical axis B4 and B1, B6 and B3 have nearly the same angles of inclinations with respect to the normal N1. Hence, the interference fringes formed on the hologram by the radiation of the object spherical waves and spherical waves for reference become parallel with respect to the thickness direction of the hologram and even if the hologram thickness fluctuates, the fluctuations in the angle of inclination of the interference fringes become slight.