Showing papers on "Phase (waves) published in 1979"

A power law phase screen model for ionospheric scintillation: 2. Strong scatter

Abstract: In this paper the weak scatter scintillation theory is reformulated to show explicitly the ramifications of an arbitrarily large ionospheric outer scale. The measured temporal phase spectrum, for example, is effectively truncated at a fixed frequency corresponding to the detrend time or the length of the data interval over which it is measured (whichever is smaller). As a consequence, the rms phase exhibits a complicated dependence on the relative irregularity drift velocity and the propagation geometry. This effect has not been included in previous analyses. By comparison, intensity scintillation data are intrinsically high-pass filtered by the diffraction process. By taking advantage of this fact a simple closed form expression for the S4 intensity scintillation index has been derived. The theory is applied to representative data sets from the Wideband satellite. The interpretation of the ionospheric parameters deduced from the analysis is also discussed.

Matrix formulation of the reconstruction of phase values from phase differences

Abstract: Methods in speckle imaging and adapative optics, as well as a new technique in digital image restoration, require the calculation of the Fourier phase spectrum from measurements of the differences on a two-dimensional grid of the phase spectrum. The calculation of phases from phase differences has been analyzed in the literature and relaxation mechanisms for computing the phase have been derived by least-squares analysis. In the following paper we formulate the phase reconstruction problem in terms of a vector-matrix multiplication, and we then show that previous solution methods are equivalent to this general description. We also analyze the errors in reconstruction and reconcile previously published error results based on simulations with an analytical error expression derived from Parseval’s theorem. Finally, we comment upon the rate of convergence of phase reconstructions, and discuss numerical analysis literature which indicates that the methods previously published for phase reconstruction can be made to converge much faster.

Modal wave-front estimation from phase derivative measurements

Abstract: Modal estimation of wave-front phase from phase derivatives is discussed. It is shown that it is desirable to minimize the number of modes estimated and the number of measurements used to maintain the quality of the estimates of low-order modes. It is also shown that mode cross coupling occurs when one tries to estimate modes higher than astigmatism.

A theoretical and experimental investigation of the modes of optical resonators with phase-conjugate mirrors

Abstract: We present an analysis of resonator properties for a cavity bounded by a phase conjugate mirror, which is generated by a degenerate four-wave nonlinear optical interaction. Using a ray matrix formalism to describe the conjugate mirror, resonator stability conditions are derived. Longitudinal and transverse mode characteristics are discussed. Results are compared with an experiment where laser oscillation was observed at 6943 A using carbon disulfide as the nonlinear interacting medium comprising the phase conjugate mirror.

Phase measurements in the frequency domain photoacoustic spectroscopy of solids

Abstract: Photoacoustic spectroscopy provides information about both the amplitude and phase of the response of a system to an optical excitation process. This paper presents a theoretical model of photoacoustic processes in the frequency domain which includes the relaxation time of the radiationless deexcitations and a two‐layer absorbing system. Emphasis is placed on the effect of these conditions on the phase of the photoacoustic signal and the utility of this measurement in evaluating material parameters. Circumstances under which the phase may be used to measure the optical absorption coefficient of the solid and the nonradiative relaxation times are defined. The value of the phase measurement in the study of surface films is discussed.

Interplanetary phase scintillation and the search for very low frequency gravitational radiation

Abstract: Observations of radio-wave phase scintillation are reported which used the Viking spacecraft having an earth-spacecraft link very similar to that which will be used in very low-frequency (VLF) gravitational-wave searches. The phase power-spectrum level varies by seven orders of magnitude as the sun-earth-spacecraft (elongation) angle changes from 1 to 175 deg. It is noteworthy that a broad minimum in the S-band (2.3 GHz) phase fluctuation occurs in the antisolar direction; the corresponding fractional frequency stability (square root Allan variance) is about 3 x 10 to the -14th for 1000-s integration times. A simultaneous two-frequency two-station observation indicates that the contribution to the phase fluctuation from the ionosphere is significant but dominated by the contribution from the interplanetary medium. Nondispersive tropospheric scintillation was not detected (upper limit to fractional frequency stability about 5 x 10 to the -14th). Evidently, even observations in the antisolar direction will require higher radio frequencies, phase scintillation calibration, and correlation techniques in the data processing, for detection of gravitational bursts at the anticipated strain amplitude levels of no more than 10 to the -15th.

Method for automatically setting the correct phase of the charge pulses in an electrostatic flow sorter

Abstract: In order to initiate the charging of droplets at a specific point in time with respect to the formation of those droplets in an electrostatic flow sorting system, the charge phase of the system of the present invention is continuously and automatically adjusted by droplet break point monitoring. The charge phase is therefore flow rate and fluid velocity independent. The break point is monitored by a light source which is focused onto the jet stream at the droplet formation break point, or close to it, and the modulation of light caused by the scatter induced by the sheath stream portion as it passes the focused beam of light is detected via the use of a suitable electro-optical detector. From the output of the electro-optical detector, after appropriate signal conditioning, an electrical wave form is obtained which shape depends upon the shape of the fluid column passing the focus beam. Using this conditioned detector output, the charge pulse phase is automatically controlled to occur at a set point in time with respect to a transition point on the waveform thus obtained. Additionally, in order to compensate for large flow rate variations, the focused beam detector can be automatically repositioned to track with the breakpoint. The correct phase of the charge pulse will accordingly continue to be derived from the breakpoint electrical waveform. Alternatively, by monitoring the jet stream at points above or below the breakpoint, the phase adjustment is possible, however, somewhat fluid velocity dependent.

Phase-jitter compensation using periodic harmonically related components

Abstract: A quadrature amplitude-modulated (QAM) data signal receiver employs a phase compensation arrangement (16, 31, 33) before the equalizer (17). The arrangement utilizes the assumption that the frequency components typically present in the phase perturbance are power-line related. This enables an effective phase compensator to be of relatively low complexity compared to the equalizer (17). Since the compensator is "pretuned", only the phase and amplitude of the frequency components need be adaptively found. This makes for a relatively stable arrangement with a suitable convergence rate. In an alternative arrangement, a phase compensator (216, 233, 240) is provided for use after the equalizer (217).

Retroreflective arrays as approximate phase conjugators.

Abstract: Arrays of corner reflectors behave similarly to nonlinear optical phase conjugators in correcting phase distortions in imaging systems. An experimental demonstration and a preliminary analysis of these properties are presented.

Variable energy standing wave linear accelerator structure

Abstract: Variable energy selection is accomplished in a side cavity coupled standing wave linear accelerator by shifting the phase of the field in a selected side coupling cavity by π radians where such side coupling cavity is disposed intermediate groups of accelerating cavities. For an average acceleration energy of E 1 (MeV) per interaction cavity, and a total number of N interaction cavities, the total energy gain is E 1 (N-2N 1 ) where N 1 is the number of interaction cavities traversed beyond the incidence of the phase shift. The phase shift is most simply accomplished by changing the selected side cavity configuration mechanically in repeatable manner so that its resonant excitation is switched from TM 010 mode to either TM 011 or TEM modes. Thus, the total energy gain can be varied without changing the RF input power. In addition, the beam energy spread is unaffected.

Method and apparatus for radiant energy modulation in optical fibers

Abstract: Radiant energy is caused to modulate in phase and frequency in a single mode optical fiber by means of a relatively movable, spatially periodic perturbation

Scattering by linearly vibrating objects

Abstract: The scattering problem for a plane wave incident upon a perfectly conducting linearly oscillating object is investigated both theoretically and experimentally. The theoretical analysis, accurate to order v/c where v and c axe the velocities of object and light, respectively, shows that the target oscillation changes the scattered far field of a motionless target only in phase. The oscillation is assumed to be periodic, and this period is shown to be impressed on the scattered field. Spectral analysis of the modulation shows that the power distribution varies with the shape of the motion, wavelength of the incident field, and the magnitude of the projections of the oscillation in the direction of incidence and receiver. Power spectra have been calculated for square, triangular, and sinusoidal target motion and, in general, the power content in the higher harmonics is found to increase with cartier frequency and magnitude of oscillation. For backscattering from an object moving sinusoidally along the direction of incidence, the power in the first harmonic is shown to exceed that at the carrier frequency when d > 0.23\lambda where d is the magnitude of the oscillation. These calculations are shown to agree with experimental measurements of the phase modulation of the field scattered from a vibrating disk at the X -band. Experimental results were obtained with continuous wave backscatter equipment at 10 GHz that utilized separate tunnel antennas for transmitting and receiving. The receiving section of this equipment was modified to separately display phase modulation and amplitude modulation characteristics of the backscattered signal in both time and frequency, as well as characteristics of the overall modulation envelope. Phase modulations introduced by target oscillations as small as \pm 0.001 in were readily detected, as were amplitude modulations of a few percent.

Interferometric measuring method

Abstract: Two radiation components differing from each other with regard to their state of polarization or their wavelength are directed onto closely adjacent points of the object to be measured. The reflected components are recombined and are fed to a polarization- or wavelength-dependent phase shifter periodically shifting the phase positions of the two components by λ/2 against each other. A phase shift of one of the components caused by the object to be measured is fully compensated for by periodically shifting the phase position of the other component at particular points in time, which can be determined, for example, by means of a connected analyzer and a photodetector. The values of the control voltage effecting the periodical phase shift in the phase shifter are measured at those points in time at which the phase difference between the two components equals zero. These values are proportional to the difference in height between the points of incidence of the two radiation components on the object surface or the slope of the object surface.

Method for the contactless measurement of the potential waveform in an electronic component and arrangement for implementing the method

Abstract: A method for the contactless measurement of the potential waveform in an electronic component with a scanning electron microscope in which the electron beam is aimed at a measuring point of the integrated circuit until at least one phase range of the measuring voltage is determined by phase-shifting the pulses of the primary electron beam with respect to the measuring voltage and subsequently, the electron beam jumped to at least one further measuring point where a phase range is determined in the same manner permitting measurement of the potential waveform at different points of the integrated circuit and displayed together on a picture screen.

Digitally programmable phase shifter

Abstract: A phase shifter is disclosed which provides a reference-phase square-wave as a first output and a second square-wave of the same frequency as the reference-phase square-wave and having the phase thereof shifted, with respect to the reference-phase square-wave, synchronously by a phase increment which is programmable in steps equal to 360/2 N degrees, where N is an integer equal to number of stages in a shift register receiving binary phase control information.

The solar-cycle period-amplitude relation as evidence of hysteresis of the solar-cycle nonlinear magnetic oscillation and the long-term (55 year) cyclic modulation

Abstract: A new dynamical model of the solar cycle has predicted that the cycle should have a hysteretic nature: the behavior of each 11 year cycle should depend on previous cycles. In the light of this new understanding of the dynamical mechanism of the solar cycle, Waldmeier's (hypothetical) law was examined as a yet unexplained characteristic of the cycle by studying the observed sunspot frequency curve. Contrary to this hypothetical law, however, it was found that sunspot cycle curves did not form a single-parameter family characterized by the maximum amplitude of the cycle. The evolutionary trajectories in period-amplitude phase space verified the hysteretic nature of the observed cycle and revealed long-term (55 year instead of the previously claimed 80 year) periodic modulations, called here 55 year grand cycles. Each 55 year grand cycle forms a loop in the phase space, and the characteristics of each 11 year cycle depend on its position in the ascending or descending phase of the grand cycle. This new law was analyzed by the nonlinear multiple-period dynamo oscillation model which has predicted the hysteretic nature. The era from cycle 11 to cycle 15 turned out to be an anomalous one characterized by alternating amplitudes for oddmore » and even cycles. Cycles 16--20 seem to constitute one grand cycle. If this is true, cycle 21 would be the beginning of another grand maximum and the model predicts that its duration would be short.« less

QPSK Suppressed carrier with rotating reference phase

Abstract: A suppressed carrier signal is offset quadrature phase shift key modulated so the reference carrier phase is stepped 90° in the same direction in synchronism with sequential bits of a serial data stream and is further bi-phase modulated in response to the binary data source having first or second binary values. A coherent receiver responds to the suppressed carrier signal to establish an equivalent sequence of stepping reference phases at the carrier frequency. The reference phases synchronously rotate in 90° increments in the same direction as the suppressed carrier reference, being permitted a four-fold initial phase ambiguity (0°, 90°, 180°, and 270°). The rotating reference phase is compared in a bi-phase manner with the appropriate component of the suppressed carrier signal to derive sequential d.c. polarities indicative of the binary bit values during the sequential binary data bits.

Initial phase analysis of R waves from great earthquakes

Abstract: Phase equalization was carried out for R waves in order to obtain information on source mechanisms of four earthquakes, the Kurile earthquake of 1963, its largest aftershock, the Rat Island earthquake of 1965, and the Tokachi-oki earthquake of 1968. The initial phase was computed using the corresponding complete great-circle phase velocity, so that influences of the lateral heterogeneity of the earth's structure were considerably reduced. The fault length of the Kurile earthquake was determined from the initial phase radiation pattern on the basis of a simple propagating fault model. There is no trade-off in this method between the fault length and the rupture velocity. Such a trade-off is inherent to the conventional directivity method. A fault length of 250 km was obtained, which was found to be nearly equal to the length of the aftershock area. We have introduced a dynamic fault parameter ‘source time’ that can be determined from the phase measurement using the complete great-circle phase velocity rather than the average phase velocity of the individual multiple R waves. This quantity corresponds to the rise time of the source time function of an equivalent point source. Source times of 97, 62, 174, and 115 s were obtained for the above four earthquakes.

The imaginary components of T=1 nucleon-nucleon phase-shifts and their effect on spin-dependent inelastic cross sections

Abstract: By means of a model involving the Delta (1236), an improved set of imaginary components for the T=1 nucleon-nucleon phase-shifts is obtained. These phase-shifts are then used to calculate inelastic nucleon-nucleon cross sections below 720 MeV, including the spin-dependent inelastic cross sections Delta sigma Ti and Delta sigma Li.

Dispersion-free amplification and oscillation in phase-conjugate four-wave mixing in an atomic vapor doublet

Abstract: This paper presents theoretical and experimental descriptions of a novel application of the dispersion-free point associated with a pair of adjacent doublet transitions in atomic and molecular systems. At this point it is possible to observe enormous pulse amplification of a phase-conjugated wavefront and intense visible oscillation without mirror feedback in the degenerate four-wave parametric mixing in sodium vapor doublet at the characteristic wavelength of 5894 A. At the dispersion-free point one also observes an ac Stark-free condition which permits the generation of a new type of coherent optical radiation called "cooperative phased-array radiation" (COPAR) from a phased-array system of coherently excited atoms in the medium at the wavelength.

Phase conjugate correction for high gain amplifier systems

Abstract: A laser provides light of a first frequency ω+Δ along a first optical path, the light being focused by optics onto a target disposed at the primary focal plane of the optics. A laser amplifier is disposed along a second optical path which receives light reflected from the target and processed through a portion of the optics. This amplifier transmits, substantially unamplified, light at the first frequency ω+Δ and amplifies light substantially at a second frequency •. Phase conjugation apparatus is disposed along the second optical path and provides light which is the phase conjugate of light incident thereupon. The phase conjugated light is provided at the second frequency ω and directed back through the laser amplifier for amplification thereof and through the optics to the target. The phase conjugated light self-corrects for optical distortions introduced into the light caused by the optics and laser amplifier, resulting in a nearly diffraction-limited high-power light beam impinging upon the target. Four specific embodiments are provided which employ stimulated Brillouin scattering, three-wave mixing, four-wave mixing and photon echo processes, respectively, in the phase conjugation apparatus.

Optical phase measurement in real time

Abstract: A method has been developed for the real-time measurement of optical phase. The optical wave whose phase is to be measured is interfered with a spatially coherent plane-wave reference on the face of a photodetector array. The irradiance is measured simultaneously at all array elements for each of three specific phase shifts of the reference, and the phase and magnitude at each array element are calculated from the three measured irradiances by a simple algorithm. The method can be used for hybrid optical-digital analog computation of 2-D Fourier transforms: information is introduced coherently into the front focal plane of a lens with a spatial light modulator, and the phase and magnitude are measured in the back focal plane. Experimental results of the Fourier transform technique are described.

Power frequency converter

Abstract: A power converter which provides precise waveshape regulation. An input pr waveform (three-phase or single phase power) is rectified and modulated to form a chopped waveform within an envelope defined by the rectified input waveform. The modulation is removed by passing the chopped signal through a low-pass filter. The output of the low-pass filter, which is equal to the instantaneous value of the chopped waveform envelope times the instantaneous value of the duty cycle of the chopped waveform, is converted to a complete sine wave output voltage in a power inverter. The output of the power inverter is sampled and compared with a low-power reference waveform in a differential amplifier. The output of the differential amplifier is phase compensated for the effects of the low-pass filter and applied as an error signal to a pulse-width-modulated oscillator to adjust the duty cycle of the chopped waveform so that the sine wave output voltage follows the reference waveform.