Showing papers on "Phase (waves) published in 1972"

Direct phase detecting system.

Abstract: A system for extracting the phase components of an optical traveling wave field has been constructed. This system consists of the Mach-Zehnder interferometer to capture the wave field as the hologram, a photoelectronic scanning system, and an analog computing circuit. The detected phase signal is immediately displayed on a cathode ray tube as continuous-tone patterns. The method has been confirmed through the experimental results.

Phase‐matchable nonlinear optical interactions in periodic thin films

Abstract: A proposal for a new method of phase matching in nonlinear optical interactions is made. A periodic perturbation of the surface of a thin‐film waveguide generates space harmonics with new propagation constants which can be phase matched. An analysis of this proposal shows it to be particularly interesting for a class of thin‐film nonlinear devices using the cubic optically isotropic semiconductors (such as GaAs, GaP, etc.) which possess high nonlinear optical coefficients but are not phase matchable by the conventional birefringent techniques.

Linear amplification with nonlinear devices

Abstract: Available nonlinear amplifying devices are used to produce bandpass linear amplification of a signal having amplitude variations. The input signal is transformed into two constant amplitude phase modulated components which together contain in their phase fluctuations the total information content of the input. The components are amplified separately by devices which preserve phase, and the recombination of the amplified components reproduces a linearly amplified replica of the original input. The technique is primarily useful at high frequencies and can be modified to provide frequency translation.

Nonlinear waves in a Kelvin-Helmholtz flow

Abstract: Nonlinear waves on the interface of two incompressible in viscid fluids of different densities and arbitrary surface tension are analysed using the method of multiple scales. Third-order equations are presented for the space and time variation of the wavenumber, frequency, amplitude and phase of stable waves. A third-order expansion is also given for wavenumbers near the linear neutrally stable wave-numbers. A second-order expansion is presented for wavenumbers near the second harmonic resonant wavenumber, for which the fundamental and its second harmonic have the same phase velocity. This expansion shows that this resonance does not lead to instabilities.

Atomic timekeeping and the statistics of precision signal generators

Abstract: Since most systems that generate atomic time employ quartz crystal oscillators to improve reliability, it is essential to determine the effect on the precision of time measurements that these oscillators introduce. A detailed analysis of the calibration procedure shows that the third finite difference of the phase is closely related to the clock errors. It was also found, in agreement with others, that quartz crystal oscillators exhibit a "flicker" or |ω|-1type of noise modulating the frequency of the oscillator. The method of finite differences of the phase is shown to be a powerful means of classifying the statistical fluctuations of the phase and frequency for signal generators in general. By employing finite differences it is possible to avoid divergences normally associated with flicker noise spectra. Analysis of several cesium beam frequency standards have shown a complete lack of the |ω|-1type of noise modulation.

Laser Interferometer for High Sensitivity Measurements on Transient Phase Objects

Abstract: A He-Ne laser beam is sent through a common path differential interferometer and the interference signal is detected by a p-i-n photodiode. Weak phase objects can be examined because optical path changes can be resolved to 0.1 A with a time resolution of about 20 ns. Examples for different gas-dynamic investigations show good results and demonstrate the wide field of application for this type of laser interferometer.

Acoustic-surface-wave amplitude and phase measurements using laser probes

Abstract: The investigation of acoustic-field distributions on free surfaces is important in several different classes of application. Measurements of the phase of acoustic surface waves using optical probes allow direct measurement of their velocity. A number of different optical-probe types are compared on the basis of sensitivity and stability. The operation and design of an optical heterodyne probe, capable of high-precision phase and group-velocity measurement, is described.

Theory of parametric oscillation phase matched in GaAs thin-film waveguides

Abstract: The operation of a parametric oscillator phase matched in a GaAs thin-film waveguide is considered. Parametric equations of motion for interacting waveguide fields at three frequencies are developed. From these equations we derive expressions for parametric gain and oscillation threshold. A specific orientation of GaAs allows optically smooth cleaved surfaces to form the oscillator cavity. Conditions for which three waveguide modes at three different frequencies can be phase matched are presented for several specific waveguide-substrate structures. These conditions are in each case determined for a wide variety of mode orders, for a laser pump wavelength of 1.06 μ, and for a large range of signal wavelengths. The deviation in thin-film thickness that can be tolerated while maintaining phase matching over a given interaction length is calculated. We find that transverse coupling strength and oscillation threshold powers are widely variable for different phase matched mode order combinations. Oscillator frequency tuning is investigated by first deriving expressions for variations in waveguide parameters required to effect tuning over a specific range and then evaluating these expressions for some of the previously determined phase-matching situations.

Quantitative visualization of large variation phase objects

Abstract: This paper describes a technique by which a large variation phase object may be visualized in an image having an irradiance which is directly proportional to the object phase. An image of the phase object derivative is formed in a coherent optical system and recorded on photographic film. This photograph is used as the input to a second coherent optical system, in which the image is an integral of the input. No limitations are imposed on the maximum object phase, only on its maximum slope. Experimental techniques for implementation of this system are discussed and results shown.

Random phase shifters for Fourier transformed holograms

Abstract: The random phase shifter method for Fourier transformed holograms is discussed. It is shown that by adopting the random phase shifters of the phase quantization levels beyond 2 (4, for example), the effectiveness becomes about twice that of 2, and that the reduction of the effectiveness by the coincidence between a pattern of the information and a phase shifter can be withdrawn under the probability of 10(-10). Hologram memories of information storage density of 10(5) bits/mm(2) and 2.0 x 10(3) characters/ mm(2) are demonstrated.

Experimental Observation of Nonlinear Wave-Particle Interactions in a Weak Cold Beam-Plasma System

Abstract: Nonlinear evolution of a beam-plasma instability has been investigated by direct measurements on the energy distribution of beam electrons and the field intensity of an externally driven electrostatic wave. The initial exponential growth of the excited single wave is halted when the wave traps the electrons and rotates them in phase space. At the phase of spatial bunching of the beam, its harmonics are observed to have maximum values. The results agree with those predicted by a single wave model.

Apparatus and methods for scanning phase profilometry

Abstract: This disclosure depicts methods and apparatus for detecting minute phase variations on reflective or transmissive specimens. A scanning phase profilometer is depicted which includes means for producing from a coherent input light beam a set, here shown as a pair, of distinguishably coded interrogating beams which are focused and scanned across a specimen as a pair of slightly displaced light spots. The interrogating beams are recombined after interaction with the specimen. Phase demodulating means are provided including a light responsive means in the path of the recombined interrogating means for detecting phase variations between the interrogating beams caused by optical path length variations as the beams are scanned across the specimen. Means are provided for producing an electrical phase differential signal characterizing the detected phase variations and electrical integrating means for integrating the phase differential signal to produce a signal characterizing the phase profile of the scansion across the specimen. Methods and apparatus for producing a two-dimensional display of the phase profile of a specimen are also disclosed.

Absolute Accuracy of the Pulse‐Echo Overlap Method and the Pulse‐Superposition Method for Ultrasonic Velocity

Abstract: It is shown that the errors in the absolute values of the measured delay times (after correction for diffraction phase and bond thickness) in the pulse‐echo overlap and the pulse‐superposition methods can be less than 0.015τ and 0.027τ, respectively, where τ is the period of the fundamental radio frequency of the transducer used. If broad‐band pulses are used with the pulse‐echo overlap method, then the error is larger but still less than 0.10τc at the center frequency. Translated into fractional errors in the single round‐trip delay time, the errors may be as small as a few parts per million. It is emphasized that the diffraction phase can introduce an error up to 0.25τ if the diffraction phase correction is not applied. Empirical methods for finding some contributions to the total error are given.

Optical limited scan antenna system

Abstract: This invention relates to an optical antenna system including an aperture lens, a feed lens and a feed array for scanning a pencil beam or multiple simultaneous beams over a limited angular sector with good sidelobe levels and minimum gain degradation. Both amplitude and phase distributions over the aperture lens are controlled for all scan angles. Also, the feed lens may be positioned in a manner such that virtually the entire aperture lens is illuminated for all scan angles thereby minimizing the size of the aperture lens, energy spillover and rate of gain decrease with angle from boresight.

Electro-optic variable phase diffraction grating and modulator

Abstract: An electro-optic variable phase diffraction device is described for varying a phase diffraction grating and modulating an optical wave. A layer of electro-optic material whose index of refraction may be varied with an electric field is placed in interacting relationship with an optical wave passing through a thin-film optical waveguide. An array of parallel spaced electrodes whose widths are substantially more narrow than the width of the optical wave are so located over the optical waveguide to form longitudinal segments in the electro-optical material for interaction with different adjacent components of the optical wave. A controlled electrical energization of the electrodes causes a corresponding change of refractive index of underlying interacting segments to form a diffracted output optical wave whose intensity is modulated in correspondence with the electrical energization. Various embodiments and methods of modulation are described.

Return-wave, phase controlled adaptive array

Abstract: In accordance with one embodiment of the invention received energy from selected subapertures of an energy transmission and reception system is spatial modulated with respect to an image plane stop structure so as to produce at the output of a detector disposed behind an aperture of the image plane stop structure, modulation components indicative of the relative phase relationship associated with each subaperture receiving path. The modulation components are applied to control variable phase shifters, in common transmission and reception paths of the selected subaperture channels, in such a manner that the optical intensity of the image field transmitted through the stop structure is maximized - that is the received image is centered on the stop aperture and the image spread is reduced to the minimum. The transmitted energy, which is applied through the phase shifters adjusted with respect to the phase relationship sensed from the received signals, is thereby correctly phased to cause maximum energy to be applied to the target.

Laser Magnetic Resonance Spectrum of NO2 at 337 μm and 311 μm

Abstract: The Zeeman components of several rotational transitions of nitrogen dioxide have been observed in absorption using the 311 and 337 μm lines of an HCN laser as a source. The Zeeman components of four rotational transitions (two at 311 μm and two at 337 μm) have been assigned. Two components of the g tensor have been determined from the spectrum by least square fitting. The anisotropic component (aa)g(S), obtained as −0.010, agrees well with that predicted from theory, but the isotropic component (0)g(S), obtained as 2.013, does not agree satisfactorily with theoretical prediction or with solid phase measurements both of which give 1.9997. The rotational frequencies of the four transitions have also been obtained.

Automatic sector indicating direction finder system

Abstract: An automatic sector indicating direction finder system which incorporates a receiving antenna arrangement incorporating four separate antenna patterns, each having a field pattern which is a function of the azimuth angle, the apparatus forming antenna signals which are then transferred through a plurality of antenna sequencing relays to a dual channel receiver. The dual channel receiver is connected to the four antennae in a timed sequence. The two outputs of the dual channel receiver are applied to phase detectors and amplitude detectors which determine the relative amplitude ratios. These ratios and the phase measurements are stored in memory momentarily and are then strobed from memory through a hard wired decoding logic circuit to an external display. The display breaks the 360* of azimuth into sixteen sectors, all equal in size, and indicates the sector location of a target.