Showing papers on "Phase (waves) published in 1971"

Temporal-Frequency Spectra for a Spherical Wave Propagating through Atmospheric Turbulence

Abstract: Tatarski has found the frequency spectra for the amplitude, phase, and phase-difference fluctuations of an infinite plane wave propagating through turbulence. Many practical optical beams, used in atmospheric studies, closely resemble point sources, for which the spherical-wave theory is more applicable. The same spectra, calculated for spherical waves, reveal contributions at higher frequencies for amplitude scintillations, nearly identical phase results, and a phase-difference spectrum with no nulls, in contrast with the plane-wave results. Comparison with recent data is shown.

Injection locking of microwave solid-state oscillators

Abstract: Simple theory indicates a phase range of from 0° to ±90° when phase locking oscillators, but these limits do not apply where Q(ΔΩ/ω 0 ) is not small. This can cause problems in multiple-source devices and other locked oscillator systems where small phase angles are desirable.

Vehicle guidance system

Abstract: A vehicle guidance system includes first and second current-carrying conductors defining a portion of the vehicle guide path and in which current flows. The current in one conductor is equal in magnitude to 90 DEG and out of phase with the current in the other conductor. The conductors, when located in a parallel substantially overlapping relationship, establish a magnetic field having an effective phase different from the phase of the current in either conductor. The conductors are separated at at least one point of divergence to define separate vehicle guidepaths. A sensor unit on the vehicle sense the magnetic field of the conductors and controls the steering of the vehicle. The circuit which responds to the sensing unit is selectively controlled so that an output signal from only one or the other of the conductors controls the vehicle steering. In addition, the sensor unit which is on the vehicle senses data located along the guidepath in the form of lobes or nodes defined by the conductors. Furthermore, the sensor functions to sense phase modulation in the guidepath conductors as controlled from a central processor, and additional circuit means senses a change in phase modulation in the current flowing through the conductors and provides an output in response thereto so that data can be transmitted to the vehicle by phase modulation of the current transmitted through the guidepath conductors.

Enhancement of optical second harmonic generation by utilizing the dispersion of air

Abstract: The dispersion of air, which causes a phase shift of 27.4°/cm between optical waves at 1.06 and 0.53 μ, has been used to compensate for phase shifts between the fundamental and second harmonic in a two‐pass second harmonic generation experiment. Use of this dispersion enables the net phase shift to be adjusted to zero, doubling the effective interaction length of the nonlinear crystal. The extension of this technique to multiple‐pass experiments is discussed, and applications to internal harmonic generation are treated.

The method of multiple scales and non-linear dispersive waves

Abstract: The method of multiple scales is used to analyze three non-linear physical systems which support dispersive waves. These systems are (i) waves on the interface between a liquid layer and a subsonic gas flowing parallel to the undisturbed interface, (ii) waves on the surface of a circular jet of liquid, and (iii) waves in a hot electron plasma. It is found that the partial differential equations that govern the temporal and spatial variations of the wave-numbers, amplitudes, and phases have the same form for all of these systems. The results show that the non-linear motion affects only the phase. For the constant wave-number case, the general solution for the amplitude and the phase can be obtained.

Millimeter wave holographic imaging of concealed weapons

Abstract: Experiments are described in which optical images of small metallic objects were reconstructed from millimeter wave phasigrams (phase-only holograms). Since the well-established term HOLOGRAM introduced first by Gabor implies a "total record," namely of amplitude and phase, the term phase-only hologram would be contradictory. The authors propose the term PHASIGRAM for a "phase record" based on the Greek work "phasis" for phase. Sufficient resolution is present in the images obtained to allow the identification of a toy metallic gun, even when covered with a layer of clothing or synthetic leather. The phase distribution of the 70-GHz millimeter wave field scattered by the object was determined by mechanically scanning a harmonic mixer over a 0.75-m diameter circular aperture in a spiral pattern. The resulting electrical phase signal was converted to a light intensity pattern which was recorded on photographic film. A He-Ne laser was used to illuminate a reduced transparency replica of the recorded phasigrams and reconstruct the images.

Observations of rapid fluctuations of intensity and phase in pulsar emissions.

Abstract: Pulsar emission data, presenting average phase shapes and pulse to pulse intensity fluctuations

Optical low pass filter

Abstract: An optical low-pass filter which is inserted in an image forming optical system in order to attain the response to zero in a frequency over the cut-off frequency and which is adapted so that the response in said optical system may not undergo a change depending upon the variation of F-number of the optical system The filter gives a blur to all images formed by said image forming optical system, and is composed of phase elements provided on a transparent base plate The phase elements are disposed systematically on a base plate for giving the phase difference to the wave front of light ray incident upon said transparent base plate

Phase variations in atmospheric optical propagation.

Abstract: Temperature structure in the atmosphere, transported by the wind across a laser beam, produces time variations in the optical path length. Using a He-Ne laser (0.6328 μm) on a 70-m propagation path, we measured the optical phase variations at four different spacings, ρ≤30 cm. Simultaneously, a midpath measurement of wind velocity and temperature structure parameter, CT2, provided the necessary meteorological measurements to compare the observed phase structure function with Tatarski’s theoretical curve. We obtained excellent agreement between theory and experiment. Direct measurements of the outer scale of turbulence, taken continuously over a 24-h period at a height of 1.6 m, indicated an average outer scale of 1.3 m with diurnal variations of ±20%. The frequency spectrum of the received phase difference at each of the four spacings is plotted and its implications for the data-sampling rate are examined. The curves obtained exhibit excellent agreement with the predicted spherical-wave phase-difference frequency spectrum.

Timing and measuring methods and means for laser distance measurements

Abstract: An improved laser distance measuring apparatus of the type that automatically calculates distance to a remote reflection target based upon a measured phase difference between a modulated transmitted laser beam and a reflected return beam from the remote target. The improved apparatus incorporates means for insuring that phase measurements for the return beam are made only when the amplitude of the demodulated return signal is within predetermined limits thereby insuring a desired degree of accuracy for the resulting phase measurement. Furthermore, rather than performing an absolute phase difference measurement, better overall accuracy is obtained by calculating a relative phase difference corresponding to the difference between external and internal reflected beam path distances. Since reflected laser beam components usually exhibit rather severe scintillations due to rapidly changing atmospheric conditions over the beam path length, means are disclosed for insuring that successive phase difference measurements are taken from different packets or bunches of reflections thus insuring that an average of several such measurements is not taken from only a single packet and hence insuring that the resultant average measurement more accurately represents the true distance to the remote target site. In addition, added electrical phase shift means are switched into operation for substantially one-half of the predetermined number of distance measurements on the most critical phase measurements to substantially cancel nonlinearities inherent in such measurements due to corresponding nonlinearities in the demodulated return signals having a significant harmonic content therein. Furthermore, when the detectable phase difference measurement is less than a predetermined limit, there is a possibility of phase ''''jitter'''' causing a counter ''''stop'''' signal to occur before the counter ''''start'''' signal thereby resulting in erratic counter operation and correspondingly erroneous phase measurement. Accordingly, means are provided for detecting such an ''''overlap'''' condition and for automatically accepting the second instead of the first available ''''stop'''' counter signal whenever such overlap conditions occur thereby introducing an additional 180* phase difference which is then compensated by complementing the counter in compensation for this fixed added phase difference. The net result is stable counter operation and the elimination of completely erroneous phase difference measurements due to phase jitter.

Phase-Shift Measurement of Evanescent Electromagnetic Waves*

Abstract: Phase shifts suffered by evanescent electromagnetic waves traversing an air gap between two glass prisms have been measured. Because the evanescent waves propagate parallel to the glass-to-air interface, they should be able to penetrate in a direction normal to the interface, without change of phase, although the amplitude is expected to decrease with depth of penetration. This has been confirmed by the experiment, which showed that the phase shifts are substantially independent of the width of the air gap.

Soft-modes in displacive transitions

Abstract: Displacive phase transitions which do not change the size of the unit cell may be classified under two types depending on their order parameter : in the elastic transitions, this is the amplitude of an elastic strain ; it is the amplitude of a relative displacement of the atoms in an optic transition In this last case, we prove that there always exists at least a whole plane of optical phonons, which are Raman inactive in the high temperature phase, and the frequency of which goes to zero at the transition temperature These soft modes become Raman active in the low temperature phase Should these phonons be Raman active in the high temperature phase, they would induce an elastic transition as shown by Miller and Axe : an elastic constant will pass through zero for a still finite frequency of the optical phonon In the case of an elastic transition, if the Landau theory allows it to be second order, we show by group theory that there always exists at least one sound velocity which passes through zero at the critical temperature We also prove that the optical or elastic soft mode never carries an electric field with it Nevertheless the dielectric constant becomes infinite at the transition temperature, and at low temperature is polar, either if the optical soft mode is infrared active or if the elastic mode induces a piezoelectric strain The damping effect associated with such transitions is not taken into account in this paper

On‐Frequency Masking with Continuous Sinusoids

Abstract: The detectability of brief, 1000‐Hz sinusoids added in phase or in quadrature to a continuous tonal masker (pedestal) of the same frequency as the signal was examined in the presence of a continuous wide‐band noise. The effects of signal duration, shape of the signal's energy‐density spectrum, sound‐pressure level (SPL) of the pedestal, and noise spectrum level were investigated. For conditions in which the background noise level was low, two unusual phenomena were noted: (1) a complete absence of the customary trading relation between signal power and duration; and (2) an extremely shallow masking function relating signal SPL and pedestal level. These departures from the law of temporal integration and Weber's law are consistent with a simple filter model of the ear in which it is assumed that the location of the auditory filter is altered in response to changes in the parameters of the signal and masker. A basic assumption of the model is that the location of the filter is changed in order to maximize the ratio of signal energy to masker energy at the output of the filter. For detection of a tonal signal in the presence of another sinusoid, it appears that observers can listen at frequencies far removed from that of the signal, where signal energy is as much as 40 dB down from the peak.

Digital distance measuring apparatus employing modulated light beam

Abstract: An improved distance measuring apparatus of the type that automatically calculates distance to a remote reflection target based upon a measured phase difference between a modulated transmitted light beam and a reflected return beam from the remote target incorporates means for ensuring that phase difference measurements are made only when the amplitude of the demodulated return signal is within predetermined limits and therefore that the desired degree of accuracy for the resulting distance calculation is obtained. Additionallly, means are included for ensuring that successive phase different measurements are taken from time-spaced return signals in order that an average of several measurements are obtained from spaced packets or bunches of reflections ordinarily resulting from scintillations due to changing atmospheric conditions over the beam path length, and that the resultant average measurement more accurately represents the true distance to the remote target site.

A Model of Eye Movements Induced by Head Rotation

Abstract: It is well known that head rotation will induce eye movements known as rotational nystagmus, the slow phase of which compensates for head rotation fairly well, and the quick phase of which takes place intermittently in the opposite direction to the preceding slow phase. From both frequency and transient responses, it is confirmed that the slow phase velocity is proportional to the output of the semicircular canal, the main transducer of head rotation. The relationship between the canal output and the quick phase is also discussed. A simple model is proposed in which the quick phase and slow phase are separately generated. In cats under controlled ether anesthesia, it is found that both phases of the rotational nystagmus can be decomposed into primary and secondary components, and a new model of the vestibulo-ocular system is proposed which includes the simultaneous influence of these two components. The model is analyzed to find a condition where the summed effect of primary and secondary components of response constituting the slow phase of rotational ocular nystagmus can be made proportional to the canal output. Many simulation results are presented to demonstrate the validity of the model.

Interferometric Determination of the Distance Dependence of the Phase Structure Function for Near-Ground Horizontal Propagation at 6328 Å

Abstract: A triple-beam interferometer has been used to determine the transverse-distance dependence of the phase fluctuations for short, near-ground horizontal propagation paths on a meteorologically instrumented range for typical-day turbulence conditions. Experimental results are compared with the predictions of the 23-power law; it is found that the unmodified Obukhov–Kolmogorov theory does not describe the results correctly, and a considerably lower value for the exponent is observed.

Jones's Matrix Representation of Optical Instruments. I: Beam Splitters.

Abstract: A general method is provided for constructing Jones’s reflection and transmission matrices of any beam splitter. Derivations are presented for the various known configurations. The method uses Abeles’s matrices and pays special consideration to the different expressions of Jones’s matrices relative to the various beams in an interferometric arrangement. The reversibility of the beam splitter in its action on the amplitude or phase, or both, of an incident light is studied. It is finally suggested that, even for an asymmetric beam splitter configuration, the symmetry of the interferogram can still be preserved by adjusting the thickness of the beam splitter in a prescribed manner.

Variable center frequency filter

Abstract: A system for analyzing the frequency response of apparatus such as rotary machinery includes a plurality of vibration sensors which are multiplexed to apparatus utilizing amplitude sensitive phase detection with a two phase clock operating at a selected frequency at which the analysis is to be performed. The two phase-detected waves are passed through vector solution apparatus which provides the summation of the rectified waves and a weighted rectified difference in the rectified waves. Various two phase clock controls and filters are disclosed.

Synthesized four channel stereo from a two channel source

Abstract: This invention relates to a synthesized four channel output from a two channel stereo source. The invention operates on left and right ((L), (R) input signals to produce difference signals (L-R), (R-L) by combining a left signal with a phase shifted right signal and by combining a right signal with a phase shifted left signal. The amount of phase shift introduced on each phase shifted signal is frequency dependent and varies from 0 DEG -180 DEG with low frequency components being 180 DEG out of phase and the high frequency components substantially in phase. In addition another phase shift is introduced on at least one difference signal, to place a phase shift of less than 90 DEG between the two difference signals. The two difference signals are then fed to the rear speakers in a four channel reproduction system.

Note on antenna pattern synthesis using numerical iterative methods

Abstract: Numerical iterative methods such as the steepest descent are shown to be a very powerful tool for pattern synthesis since they take full advantage of all available parameters such as element spacings, current's amplitudes and phases, pattern phase when not specified, and even frequency. Furthermore, the method allows the introduction of linear and nonlinear constraints in all parameters with no special difficulty.

Determination of the ellipticity of light and of optical constants by use of two reflection polarizers.

Abstract: A method is described which allows the determination of the ellipticity of light (i.e., the degree of polarization as well as the phase difference of the mutually perpendicular electric field components) by intensity measurements behind two reflection polarizers. The method yields simultaneously the complex reflection coefficient of the first polarizer and its optical constants if it consists of only one mirror. The method is especially suited for the extreme ultraviolet where neither transmission polarizers nor simple phase shifters are available.

A 360/spl deg/ Reflection-Type Diode Phase Modulator (Correspondence)

Abstract: A 360/spl deg/ phase modulator using two series-tuned varactors in a parallel connection is described. The design minimizes the change in total phase shfit with frequency and gives a small attenuation ripple. The modulator is centered at 2 GHz and gives a total phase shift at 360/spl deg/ at the center frequency, an attenuation ripple of 1.3 dB over a 10-percent bandwidth and a 7/spl deg/ decrease of phase shift at the band edges.

X‐ray holographic interferometry in the determination of planar multilayer structures. Theory and experimental observations

Abstract: A theoretical treatment of X-ray diffraction from composite multilayer systems is given. These systems consist of two or three structures placed beside one another, each containing a number of different bimolecular leaflets as unit cells. Phase information for one of the structures in the composite system can be obtained, if another structure in the system is known precisely, from the interference of X-ray photons diffracted by the known structure with photons diffracted by the unknown structure. The experimental feasibility is demonstrated in an X-ray diffraction experiment.

Amplitude-modulated eight-phase phase-modulation system

Abstract: A multiple modulation system for obtaining an amplitude-modulated eight-phase phase-modulated wave employed for transmitting three channels of binary information, in which the amplitude of an eight-phase phase-modulated wave is deviated by substantially six decibels when the eight-phase phase-modulated wave assumes any of four phase-positions alternately predetermined from possible eight-phase positions.

Generalized phase shifts for a cluster of muffin‐tin potentials

Abstract: Starting with the partial wave method generalized to non-spherically symmetric potentials by Demkov and Rudakov a purely algebraic scheme is proposed how to calculate the generalized phase shifts for a cluster of non-overlapping muffin-tin potentials. These cluster phase shifts and the corresponding partial wave amplitudes are determined by a system of homogeneous linear equations, into which the phase shifts of each muffin-tin potential and the structure enter separately, completely similar to the KKR method for the band structure of a crystal. By the proposed scheme bound states can also be calculated, the number of which is limited by the properties of cluster phase shifts. As a mathematical remedy an addition theorem about the spherical Neumann functions is derived. [Russian Text Ignored].