Showing papers on "Phase (waves) published in 1980"

Wave-front estimation from wave-front slope measurements

Abstract: The problem of wave-front estimation from wave-front slope measurements has been examined from a least-squares curve fitting model point of view. It is shown that the slope measurement sampling geometry influences the model selection for the phase estimation. Successive over-relaxation (SOR) is employed to numerically solve the exact zonal phase estimation problem. A new zonal phase gradient model is introduced and its error propagator, which relates the mean-square wave-front error to the noisy slope measurements, has been compared with two previously used models. A technique for the rapid extraction of phase aperture functions is presented. Error propagation properties for modal estimation are evaluated and compared with zonal estimation results.

Signal reconstruction from phase or magnitude

Abstract: In this paper, we develop a set of conditions under which a sequence is uniquely specified by the phase or samples of the phase of its Fourier transform, and a similar set of conditions under which a sequence is uniquely specified by the magnitude of its Fourier transform. These conditions are distinctly different from the minimum or maximum phase conditions, and are applicable to both one-dimensional and multidimensional sequences. Under the specified conditions, we also develop several algorithms which may be used to reconstruct a sequence from its phase or magnitude.

Intuitive explanation of the phase anomaly of focused light beams

Abstract: An intuitive argument is presented for the phase anomaly, that is, the 180° phase shift of a light wave in passing through a focus. The treatment is based on the geometrical properties of Gaussian light beams, and suggests a new viewpoint for understanding the origin of the phase shift. Generalizing the argument by including higher-order modes of the light field allows the case of a spherical wave to be treated.

Approximate two-parameter phase function for light scattering

Abstract: A two-parameter phase function is described for highly anisotropic angular scattering distributions. The phase function has a convenient analytic representation since it is the generating function for the Gegenbauer (or ultraspherical) polynomials. Sample calculations illustrate the large variety of forward-to-backward scattering amplitudes and shapes that can be fit with the two parameters. Illustrative phase functions are given that approximate light scattering distributions predicted for several biological and atmospheric specimens from Rayleigh-Gans and Mie models. A suggested classification scheme for size and refractive index of microparticles in human blood is presented as a potential application of the phase function with two parameters.

Compensation for phase distortions in nonlinear media by phase conjugation.

Abstract: We demonstrate theoretically that the distortion-correction property of phase-conjugate beams propagating in reverse through aberrating media is also operative when the indices of refraction of the media depend on the intensity. A necessary condition is that the phase-conjugate mirror that generates the reflected beam possess a unity (magnitude) "reflection" coefficient.

Linear interferometric waveguide modulator for electromagnetic-field detection.

Abstract: A channel-waveguide interferometer with asymmetric arms, suitable for electromagnetic-field detection, is described. A π/2 intrinsic phase differential makes the output linearly proportional to the applied voltage (electromagnetic field). Horizontal and vertical electrode sets provide polarization-independent operation, with electrode lengths chosen to make the voltages approximately equal. In Ti-diffused devices in Z–X-cut LiNbO3, the TE- and TM-mode outputs are equally modulated with the horizontal voltage 43% of the vertical. Output linearity over a 40-dB range and operation up to 300 MHz are demonstrated.

Non-Lorentzian laser line shapes and the reversed peak asymmetry in double optical resonance

Abstract: The interaction of an atomic system with a laser having phase fluctuations is studied within the phase-diffusion model, with the finite correlation time of the time derivative of the phase taken into account. This finite correlation time introduces a line shape which is Lorentzian near the center and falls off faster than the Lorentzian at its wings. The authors apply this model to calculate the spectrum of double optical resonance for excitation by a laser having this non-Lorentzian line shape. It is observed that the reversed peak asymmetry reverts to normal far off resonance owing to the cutoff of the laser spectrum, in agreement with recent experiments. Numerical results are presented.

Distance measuring device and method

Abstract: Electromagnetic distance measurement, preferably utilizing optical signals. Signals from a main transmitter are transmitted from a first position to a second position and returned to the first position and simultaneously from the main transmitter along a first fixed length path. Two separate receiving channels are provided to receive the two signals. The phase difference between the two received signals is determined. A further auxiliary transmitter is provided and signals are subsequently transmitted from the auxiliary transmitter along second and third fixed length paths to the first and second receiving channels respectively. The phase difference between the received second and third path signals is determined, and the difference between the two phase differences obtained. This difference is then solely dependent on the distance between the two positions and the lengths of the first, second and third paths. Further, if the third path has a length equal to the sum of the lengths of the first and second paths, then the difference is dependent only on the distance between the first and second positions. The transmitted signals are in modulated form. Also, the received signals are heterodyned with a reference signal. Phase angle perturbations due to the electrical equipment is completely eliminated.

Space diversity reception system having compensation means of multipath effect

Abstract: A space diversity reception system which minimizes the inband amplitude and/or phase dispersion by controlling the phase shifter is described. According to the present invention, the interference waves in the two antenna outputs are combined in anti-phase condition. The phase shifter control direction is decided by the sign of the two parameters. One of them is difference between two antenna levels at the center frequency of the pass-band, and the other is the difference of the combined signal levels at the extreme edges of the pass-band. The control means comprises four detectors for detecting said levels, two subtractors for providing said level differences between them, and the control circuit for deciding the phase shifter control direction.

Absolute optical absorption coefficient measurements using photoacoustic spectroscopy amplitude and phase information

Abstract: In order to perform quantitative photoacoustic spectroscopy (PAS) it is desirable to have a method of obtaining the absolute absorption coefficient of a sample from PAS measurements alone. The photoacoustic signal contains both amplitude and phase data and this paper discusses a method by which this information may be used to determine the absolute absorption coefficient of condensed samples. Experimental results on ions in aqueous solution are also presented.

Fiber-Optic Rotation Sensors

Abstract: Possible approaches to the design of fiber optic inertial frame rotation sensors based on the Sagnac effect are reviewed under two general categories: (1) single frequency interferometers which generate a phase shift proportional to inertial rotation rate, and (2) dual frequency interferometers for which the beat frequency is proportional to rotation rate. The principal variations within the single frequency class involve the way in which the nonreciprocal phase bias is used and techniques for generating the nonreciprocal bias. Within the dual frequency class, the various approaches differ principally in the way in which the counter-circulating frequencies are established.

Laser heterodyne surface profiler

Abstract: Method and apparatus for testing the deviation of the face of an object from a flat smooth surface using a laser beam having two plane-polarized components, one of a frequency greater than the other to produce a difference frequency with a phase to be used as a reference. The beam also is split into its two components which are directed onto spaced apart points on the face of the object. The object is rotated on an axis coincident with one component as a reference. The other component follows a circular track on the face of the object as the object is rotated. The two components are recombined after reflection to produce a difference frequency having a phase that is shifted in an amount that is proportional to the difference in path length as compared to the reference phase to produce an electrical output signal proportional to the deviation of the height of the surface along the circular track. The output signal is generated by means of a phase detector that includes a first photodetector in the path of the recombined components and a second photodetector in the path of the reference phase. The output signal is dependent on the phase difference of the two photodetector signals. A polarizer, a quarter-wave plate and a half-wave plate are in series in the path of the reference phase. Rotation of the half-wave plate can be used for phase adjustment over a full 360° range for initial calibration of the apparatus.

Method for Equalizing Phase Velocities of Coupled Microstrip Lines by Using Anisotropic Substrate

Abstract: We present a method for equalizing the even- and odd-mode phase velocities of coupled microstrip lines with zero-thickness strips by using the anisotropic material cut in the appropriate direction as the substrate.

Linearized digital phase and frequency detector

Abstract: A digital phase and frequency detector is capable of providing a linearized transfer function. The digital phase and frequency detector includes two latches each receiving an input and each providing an output. The output of the latches is combined by a logic gate to generate a reset signal. The linearization is a result of providing a delay to the reset signal. The reset signal is used to reset the two latches within the phase and frequency comparator. This improved phase and frequency comparator eliminates non-linearities which would otherwise be inherent in its transfer function and thereby degrade performance of phase-locked systems employing the comparator. The phase and frequency detector is easily manufactured as an integrated circuit and does not require any external signals in order to eliminate the non-linear region.

Apparatus for writing digital information in a disc-shaped optically readable record carrier

Abstract: An apparatus for recording optically detectable information in a record carrier (1) provided with information areas (9) arranged in accordance with a spiral or concentric track pattern, which areas (9) alternate with synchronization areas (8) in each of which the address of the associated information area is recorded in an optically detectable manner. Recording is effected with the aid of first modulated laser beam (16a), whilst a second beam (16b) is projected after the first beam for reading the recording. The track pattern has previously been provided with a periodic track modulation of a frequency at which the power spectrum of the information to be recorded substantially exhibits a zero point. The apparatus comprises a first and a second filter for filtering a signal corresponding to the track modulation out of the first or second laser beam reflected or transmitted by the record carrier, whilst in series with the second filter there is included a delay network (51), from which a synchronization signal is available. Furthermore, there is provided a phase comparator (52) which during reading of the synchronization areas determines the phase difference between the signals obtained by means of the first and the second filter and which controls the delay network (51) in such a way that the output signal of said delay network is in phase with the output signal of the first filter.

Digital phase comparator with improved sensitivity for small phase differences

Abstract: A digital phase comparator for essentially eliminating the dead zone in the phase correction means of a phase locked loop. The digital phase comparator is arranged to provide respective up and down output pulses to operate respective charge pumps. The up and down output pulses at all times are greater than a predetermined time duration no matter how small the phase difference between comparator input signals. A delay means is provided in the phase comparator logic, which delay means substantially determines such predetermined time duration. The minimum pulse duration of the up and down signals is selected to be at least of a duration sufficient to operate its respective charge pump, thereby overcoming the finite turn on time of the respective charge pump, no matter how small the phase error.

Effect of phase and orbital wave parameter choices on CS and IOS degeneracy averaged differential cross sections

Abstract: The effect of phase choice and partial wave parameter choice on CS and IOS inelastic degeneracy averaged differential cross sections is studied. An approximate simplified CS scattering amplitude for ?=1/2(l′+l) is derived and is shown to have a form which closely resembles the McGuire–Kouri scattering amplitude for odd Δj transitions and reduces to it for even Δj transitions. The choice of phase in the CS wave function is shown to result in different approximations which yield significantly different shapes for the degeneracy averaged differential cross section. Time reversal symmetry arguments are employed to select the proper phase choice. IOS calculations of the degeneracy averaged differential cross sections of He–CO, He–Cl and Ne–HD using ?=1/2(l+l′) and the phase choice which ensures proper time reversal symmetry are found to correct the phase disagreement which was previously noted for odd Δj transitions using ?=l or l′ and either the time reversal phase or other phase choices.

Method and arrangement for the measurement of rotations

Abstract: In order to measure the rotation rate of a rotating light path by the Sag effect, a pair of phase modulated coherent light beams are passed in opposite directions along the light path. After the beams have emerged from respective ends of the light path, the intensity of one of them is detected as a measurement of the phase shift which occurs between the beams along the light path. The detected output is then passed through a synchronous rectifier to produce an error signal for a control loop for the system. In a preferred embodiment, the control loop is formed by a solenoid wound around a portion of an optical fiber located along said light path. By processing the current through the solenoid, a continuous update of a scale factor for the phase shift can be achieved. Also, interference with the phase shift in the rotating object is prevented by the structural interconnection between an input/output branching device and a beam splitter for the system utilizing the combination of a monomode wave guide and a polarizer.

Rapid oscillations in cataclysmic variables. IV. WZ Sagittae.

Abstract: An extensive study of the rapid coherent oscillations in the light curve of the dwarf nova WZ Sagittae is presented. Data in 1978 show conclusively that the 27.87 s oscillation is a clock of high stability, maintaining a constant period and a nearly constant phase for many months. A period increase of 1 part in 10/sup 5/ occurred between 1977 and 1978, and all oscillation timings during 1976-1978 can be fitted with a linearly increasing period. Random ''phase jitter'' of approx.30/sup 0/ is also found in the timings, superposed on the strictly periodic process. The mean power spectrum show weak signals at frequencies slightly lower than the fundamental frequency.

Theoretical determination of domain structure at transitions from twinned phase : Application to the tetragonal-orthorhombic transition of KNb03

Abstract: The theoretical determination of the initial domain structure and the phase boundary orientation inducing a wanted domain structure in the new phase seems to be a study of worthwhile interest. The W. L. R. theory {1} is not suitable for complex domain structure in each phase because mean distortions of the new phase cannot be expressed in terms of the older one. So, an other algorithm is proposed to solve this problem.

Phase-conjugate reflection by degenerate four-wave mixing in a nematic liquid crystal in the isotropic phase

Abstract: We report the generation of conjugate wave fronts by degenerate four-wave mixing in the isotropic phase of the nematic substance p-methoxy-benzylidene p-n-butylaniline. The temporal and spatial properties of the conjugate wave fronts are verified. The dependence of the nonlinear reflectivity on the pump-wave power and the temperature of the medium is discussed.

Ultrasonic fluid leak detector

Abstract: A device for detecting ultrasonic noise, particularly such noise as generated by fluid leaks, includes a directional ultrasonic microphone, amplifiers and ultrasonic filters, an envelope detector, an audio preamplifier and filter, a level control, a meter, an audio power amplifier and speaker, and a phase shift feedback network connected from the output of the power amplifier to an input thereof. A switch is operable in a first setting to connect the power amplifier to the level control to convey the audio frequency amplitude envelope of the detected ultrasonic noise through the speaker or in a second setting to connect the power amplifier to the feedback network. A level detector is operatively connected to the level control and provides a control signal which is conducted to the feedback network. When the control signal exceeds a selected level, the feedback loop circuit is completed, whereby the power amplifier oscillates audibly through the speaker and gives audible indication of an ultrasonic noise. The components are enclosed in a pistol shaped housing for substantially single handed aiming and operation.

Dependence of coherent nonlinear whistler interaction on wave amplitude

Abstract: Dependence of coherent nonlinear whistler interaction on wave amplitudes is investigated by both computer simulations and accompanied theoretical consideration. Six self-consistent computer simulations have been carried out for six different intitial amplitudes of whistler waves. The computer code follows Newtonian dynamics of 3072 superparticles in a self-consistent wave field. In four cases, a monochromatic whistler wave grows up exponentially and subsequently shows an amplitude oscillation around a saturation level. The saturation levels in these four cases are, however, almost the same regardless of the initial wave amplitudes. In the other two cases in which the initial wave amplitudes are larger than the saturation level of the previous four cases, the whistler wave shows neither growth nor damping but merely shows gradually decaying amplitude oscillations. The difference in nonlinear behaviors of resonant electrons in these six computer runs such as phase trapping, phase bunching, and pitch angle diffusion is also considered and discussed. A theoretical interpretation of the simulation results is given based on a rather simple model. An analytical expression for the saturation level is derived based on the model, which shows a good agreement with our simulation results.