Showing papers on "Standing wave published in 1979"

Atomic motion in resonant radiation: An application of Ehrenfest's theorem

Abstract: A new theory of atomic motion in a resonant or near-resonant electromagnetic wave, based on Ehrenfest's theorem and the optical Bloch equations, is presented. The theory provides a simple unified treatment of the radiation force, including effects of spontaneous emission and induced-dipole interactions. Analytical results are presented for a plane running wave, a general standing wave, a collimated Gaussian beam, and a combination of standing and running waves.

New experimental evidence of the periodic surface structure in laser annealing

Abstract: This letter presents a study of the nature of the periodic structure observed on the edge of laser‐annealed spots on ion‐implanted silicon. The direction of the periodic fringes was always found to be about perpendicular to the E vector of the light for linearly polarized beams. No fringe pattern was observed for circular polarization. We suggest that the pattern observed is due to heating by a standing wave resulting from the interference of the impinging wave and a radial (longitudinal) scattered wave.

Solar p-mode oscillations as a tracer of radial differential rotation

Abstract: Photoelectric observations of solar p-modes obtained with improved wavenumber and frequency resolution are presented. The observations are compared with model calculations of the p-modes, and the degree of spatial and temporal coherence of the observed wave pattern is investigated. It is found that the p-mode oscillations pervade the visible surface of the sun with a high degree of coherence in space and time, so that the whole complex pattern of standing waves with its nodes and antinodes can be regarded as a fixed pattern corotating with the solar surface layers. The p-modes are introduced as a tracer of solar rotational flow velocities. The equatorial differential rotation is estimated as a function of effective depth on the basis of the theoretical contribution functions for the p-modes recently derived by Ulrich et al. (1978). The results strongly indicate that the angular speed of rotation is not uniform even in the relatively shallow layer extending about 20,000 km below the photosphere.

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.

Deflection of a Na Beam by Resonant Standing-Wave Radiation

Abstract: In 1933 KAPITZA and DIRAC published a paper titled “The Reflection of Electrons from Standing Light Waves” in which they proposed a new experiment [1]. Fig. 1 shows a picture from their paper.

The current-driven, ion-acoustic instability in a collisionless plasma

Abstract: The current-driven, ion-acoustic instability was investigated by means of an experiment performed in a collisionless plasma produced in a single-ended Q-machine. Reflections at the ends of the plasma column gave rise to a standing wave. Parameters of the instability were investigated, and it was demonstrated that the fluctuations in the plasma column behave as a classical Van der Pol oscillator. Accurate measurements of the growth rate of the instability can be performed by making explicit use of the particular properties of such a system.

Stochastic heating of a large-amplitude standing wave

Abstract: Stochastic behavior of particle motions in an electrostatic standing wave is analyzed; its significance in supplementary heating of plasmas is discussed.

A note on numerical computations of large amplitude standing waves

Abstract: Numerical solutions of the inviscid equations that describe standing waves of finite amplitude on deep water are reported. The calculations suggest that standing waves exist of steepness, height and energy greater than the limiting wave of Penney & Price (1952). The computed profiles are found to be consistent with Taylor's (1953) experimental observations.

Production of reproducible Rayleigh-Taylor instabilities.

Abstract: A device is described that excites individual modes of the standing wave spectrum for surface waves on water in a water tank of rectangular cross section. By synchronizing the downward acceleration of the tank with the standing wave on the water, Rayleigh–Taylor instabilities with reproducible characteristics are excited at the air–water interface. By controlling the width of the tank, the fluid motion is made to be largely two dimensional. The reproducibility of the phenomenon and the two‐dimensional character of the flow make it possible, for the first time, to compare details of the wave profile with results predicted with the two‐dimensional models of Emmons, Chang, and Watson.

Cooling, trapping, and storage of atoms by resonant laser fields

Abstract: Analysis of the possiblity of cooling, trapping, and storage of atoms in the resonant field of a laser standing wave is presented. Under certain regimes of frequency scanning the laser radiation can cool atoms in low-pressure gas to the temperature T ≃ 10−4−10−3 K. Because of gradient force effects, cooled atoms will be held in the light field for a long time. Joint cooling and storage of atoms in a resonant light field is important for spectroscopic studies with an extremely high sensitivity and resolution.

Collapse of very large amplitude ion waves

Abstract: Recently extremely large supersonic amplitude ion waves have been observed in simulations of backscatter instabilities, electron beam interactions, and large amplitude Langmuir waves, which break in an unconventional symmetrical x‐type manner. The conditions necessary for this type of breaking and simulations to support this theory are presented.

Classical theory of scattering of an electron beam by a laser standing wave

Abstract: A classical theory of scattering of an electron beam by a laser standing wave (the Kapitza-Dirac effect) is presented. The prediction of the theory is in good agreement with all the experimental results which were reported independently by Bartell et al., Schwarz et al., Takeda et al., and Pfeiffer. This shows that the interaction of a free electron with coherent radiation is basically a classical process.

Axial eigenmodes for long −λ∥ waves in plasmas bounded by sheaths

Abstract: Waves such as drift waves and lower hybrid oscillations in a plasma are sensitive to the degree to which charge neutrality can be maintained by electron flow along the magnetic field. When the plasma is bounded axially, the sheath conditions on the end plates determine the parallel wavelength. It is found that the nature of the bounded modes depends on whether the motion of electrons is resistive or inertial. If it is resistive, the sheath matching conditions can be satisfied by standing waves with the proper wavelength. If it is inertial, pure standing waves are not possible; there must also be a variation of phase along B. Application is made to two‐ion hybrid waves in connection with isotope separation.

Monolithic isolated gate FET saw signal processor

Abstract: A monolithic surface acoustic wave (SAW) signal processor which combines the functions of acoustic wave interaction, nonlinear product mixing, and integration, together with rapid-scan readout capability, which may be used, for instance, in correlation of amplitude and/or phase coded signals of a duration order of magnitude larger than the total propagation delay time of the SAW device, includes launching transducers at opposite ends of an interaction region, and a plurality of interaction taps, each tap comprising a Schottky barrier field effect transistor (FET), the sources and drains of the FETs being connected in common, but each FET gate being isolated. For long code correlation of a phase shift keyed signal, a reference wave having the same carrier frequency and identical coding is launched contemporaneously therewith in a first, correlation step, a standing wave component of product mixing of the two waves being of like sign or sense at any tap where the two waves are properly in phase integrating over the total number of code chips of the waves to provide an integrated, stored charge manifestation of correlation on the isolated gate of the related tap, the taps being interrogated for an integrated indication of correlation at one of the taps by means of a pulse of width the same as the propagation delay of a single tap mixing with an extended carrier at each tap, a component of product mixing at a third frequency (sum or difference) as a consequence of enhanced mixer efficiency due to the stored charge at the correlating tap, providing an output indication of the fact of correlation and phase relationship between the two waves. Various surface acoustic wave transducer and tap structures, utilizations, and implementation techniques are discussed.

Photon Echoes in Standing Wave Fields: Time Separation of Spatial Harmonics,

Abstract: : A calculation is presented to describe the response of an atomic system subjected to two strong standing wave field pulses separated in time. One finds a sequence of output pulses following the input ones, reminiscent of classical photon echoes. A physical picture of the processes involved in echo formation is presented and connection is made with the classical picture of photon echoes. The application of these techniques to collision studies is emphasized. It is shown that studies of echoes produced by standing wave fields can prove advantageous for exploring the effects of small angle scattering on both level populations and atomic coherences. (Author)

Nonlinear disturbances in self-gravitating media

Abstract: Using a multiple time-scale method, the weakly nonlinear waves on a self-gravitating incompressible fluid column are investigated. The analysis reveals that near the wavenumberk=k c , the amplitude modulation of a standing wave can be described by the nonlinear Schrodinger equation with the roles of time and space variables interchanged. The nonlinear cutoff wavenumber, which depends sensitively on initial conditions, can then be derived from the nonlinear Schrodinger equation so obtained. The finite amplitude standing wave is stable against modulation.

Finite amplitude two‐dimensional waves in a rectangular duct induced by arbitrary periodic excitation

Abstract: The nonlinear two‐dimensional acoustic waves that occur within a rectangular duct of semi‐infinite length as the result of periodic excitation are determined by an asymptotic method. A regular perturbation expansion is employed to obtain the velocity potential as a solution of a nonlinear wave equation. Uniformly valid expressions for the particle velocity components and pressure are then derived with the aid of a coordinate straining transformation that features both spatial coordinates. The response is found to be formed from the linear superposition of nondispersive groups of propagating nonlinear waves, each of which corresponds in linear theory to a fundamental wave and all overtones having the same phase speed, together with exponentially decaying standing waves resulting from excitations below the cutoff frequency. Typical spatial profiles and temporal responses for one nondispersive group are discussed in an example.

Steady propagation of a coherent light pulse in a dielectric medium. II. The effect of spatial dispersion

Abstract: For pt.I see ibid., vol.10, p.425 (1977). The effect of spatial dispersion or exciton formation on the steady propagation of a coherent light pulse in a dielectric medium is studied. The optical Bloch equation for a lattice of atomic dipoles coupled to one another by an exchange-type interaction is solved simultaneously with the Maxwell equation by the method of power-series expansion developed in the preceding paper. Two kinds of pulse solutions are obtained in general: one propagating by the medium of the radiation field and the other by excitation transfer between atomic dipoles. The former solution is SIT-like in the short pulse limit, but a polariton-soliton or a standing wave of non-linear polariton if the pulse width is long. The latter is an exciton-soliton containing little photon component. When the pulse width is extremely long, there appears a polariton-soliton of a new type in which the two propagation mechanisms are mixed. It is found that the spatial dispersion prevents the polariton-soliton solutions from existing in a certain frequency range. This effect is explained on the basis of the functional behavior of the dispersion relation of the non-linear polariton.

Simultaneous forward and backward integration for standing waves in a resonator

Abstract: The electromagnetic field distribution in a laser resonator is obtained by the numerical solution of the paraxial wave equation with nonlinear saturated gain. In unstable res­ onators the edge diffraction at the output mirror produces high-frequency ripples in the field distribution at the exit plane of the laser. This requires one to choose a fine transverse mesh for a realistic representation of the optical field. Ideally one would like to solve the paraxial wave equation using finite difference methods, but the computer core and time requirements are prohibitively large. For this reason the thin gain-sheet approximation is often made. In this calculational procedure, the continuous gain medium is approximated by a number of discrete gain sheets. The op­ tical field is freely propagated between two such sheets and then multiplied by the total gain and phase shift lumped at the gain sheet. It was found that by employing the fast-Fourier-transform method the free propagation code can be made significantly faster than the code obtained using eigenmode expansions. However, the core requirements are still stringent. In this approach one generally saves in core the intensities of the left-going and right-going waves at the gain sheets which are needed to compute the saturated gain; the gain is also stored to be used on the next round trip inside the resonator. The amount of bare minimum storage locations needed thus is ~ (AM + 2)N, where M is the number of gain sheets and the transverse mesh consists of N points along one direction. 4MN locations are needed to store the leftand right-going intensities, gain, and phase shift at M sheets, and 2N loca­ tions are needed to store the complex field being propagated. Reflection symmetry, if present, can reduce this amount by a factor of 4. The calculations in Ref. 2 were done with N = 128 and M = 7. In this case MN ~ 100K (kilocore) and is readily available on computers. In some experimental situations, however, the high-frequency ripples in the field distribution and large gain variations along resonator axis require a choice M > 10 and N ~ 500. With this set of values MN ~ 2500K and we find that the problem cannot be solved with the present generation of computers. It is apparent that if we somehow avoid the need to store the intensities and gain at each gain sheet, a substantial reduction in core size can be achieved. In this Letter we propose the simultaneous prop­ agation of right-going and left-going waves to achieve this reduction in core size. In the paraxial approximation the leftand right-going waves satisfy the following coupled set of equations:

Physical mechanism of heat transfer from heated and cooled cylinder to water in ultrasonic standing wave field.

Abstract: It is well known that the heat transfer rate from a solid surface to a fluid is increased in an ultrasonic field, but the mechanism of enhancement of heat transfer with ultrasonics has not been elucidated sufficiently. To clarify the mechanism of heat transfer with ultrasonic irradiation, the effects of an ultrasonic standing wave of 28KHz on the free convective heat transfer from a heated or a cooled cylinder of diameter 17.5 mm to degassed water were investigated experimentally. In particular, temperature distribution near the node and the antinode of the ultrasonic standing wave were observed by the Schlieren method. The average and the local heat transfer coefficients between the node and the antinode of the standing wave from the heated cylinder to water were measured. In the case of heat transfer from the heated cylinder, the heated water near the cylinder is moved from the node to the antinode of the standing wave, whereas the cooled water near the cooled cylinder is moved from the antinode to the node. Therefore, the thermal boundary layer thickness around the cylinder is varied by movement of fluid and as a result it is considered that the local and the average heat transfer coefficient vary. An acoustic radiation pressure theory which explains the mechanism of heat transfer in an ultrasonic stnading wave field is proposed.

Nonlinear linearly polarized standing waves in a cold-electron overdense plasma

Abstract: The authors investigate the form of a standing wave in a cold inhomogeneous electron plasma, taking into account "relativistic effects." The wave amplitude is greatly modified near the critical surface for high intensities.

A study of ultrasonically induced pulsations of gas-filled channels in Elodea

Abstract: The ultrasonically stimulated pulsation of pockets of intercellular gas in Elodea has been studied using optical microscopy. The intensity dependence of the microstreaming associated with these pulsations has been measured by observing the rotation of chloroplasts and other organelles in the microstreaming vortices. The threshold energy density to produce microstreaming in a standing wave field was found to be 0.03 J m-3 at 700 kHz, equivalent to an average intensity of 5 mW cm-2 in the standing wave field, and 0.01 J m-3 at 3 MHz, equivalent to an intensity of 15 mW cm-2. The channels had resonant frequencies in the low megahertz range and the relationship between the channel diameter and the resonant frequency was found to be similar to that for a gas bubble in a liquid.

Precessional rotation and other nonlinear effects due to standing waves and other two‐wave resonant interactions in a magnetized plasma

Abstract: When two electromagnetic waves propagate along the fixed direction of an uniform and constant magnetic field in a homogeneous, cold, and collisionally damped plasma, the effects of their nonlinear interaction are large and so important in two special cases. One is the case in which the beat frequency equals the characteristic plasma frequency and moreover, one of the wave frequencies equals the gyration frequency of electrons (or ions). The other is the nonlinear evolution of the wave pattern formed by an appropriate superposition of the two waves in a manner which produces standing waves from them in the linear approximation. These two cases have been theoretically investigated in this paper. Moreover, the nonlinear evolution of the standing‐wave patterns has been discussed with a view to initiate the exploration of the application side of this effect.

Motion of relativistic particles in standing wave fields

Abstract: The motion of relativistic particles in the field produced by two circularly polarised, electromagnetic plane waves travelling in opposite directions is studied. The Klein-Gordon equation is used, i.e. spin effects are neglected, and only motion along the beam direction is considered. If the electromagnetic beam carry opposite polarisation, the particle energy shows a band structure. The transmission of a plane particle wave through a long device is calculated. Transmission occurs only if the particle energy corresponds to an allowed energy band. For other energies the particles are totally reflected. For equal polarisation a similar structure emerges for the particle momentum along the beam direction. The observation of the band structure poses serious experimental problems.