Bending wave intensity in a thick beam

I.IntroductionMeasurementSofbendingwaveintensityinoneortwodimensi0na1structuresbecomequitepopularandgetavarietyofindustria1app1icati0ns.Theexistingintensitytheory['-']wasderivedbasedontheclassicaIBernou11i-Eu1ertheorywhichisanapproximatetheoryforana-lyzingstructuralvibration.Inthe1ow-frequencylimitwherebendingwavelengthsaremuchlongincomparisonwiththethicknessofthestructurealongwhichtheypr0pagate(i.e.,thinstructurcs),theuse0ftheclassica1theorywi1lresu1tinanegligiblyerro/`].Forshortwave-1ength…     

Iterative retrieval of one-dimensional x ray wave field using a single intensity measurement

The problem of retrieving a complex function from the modulus of its Fourier transform has non-unique solutions in one dimension. Therefore iterative phase retrieval methods cannot in general be confidently applied to one-dimensional problems, due to the presence of ambiguities. We present a method for a posteriori reduction of the ambiguities based on the correlation analysis of the solution of a large number of runs of an iterative phase retrieval algorithm with different random starting phases. The method is applied to experimentally measured diffraction patterns from an x ray waveguide illuminated by hard x rays. We demonstrate the possibility of retrieving the complex wave field at the exit face of the waveguide and compare the result with theoretical prediction.     

Anomalies in the field of a gaussian beam near focus

A theoretical analysis of the electromagnetic field of a focused gaussian beam, like that produced by some lasers, indicates anomalies in the field distribution over the focal region. The transverse component of the electric field is shown graphically in this region using data obtained through the numerical integration of an expression that is exact according to Maxwell's equations. These data agree with the standard paraxial theories used to describe gaussian beams only asymtotically, in the limit of zero beam divergence about focus. As the divergence is increased, so that the beam is brought more sharply to focus, the gaussian beam evolves toward a dipole field from which all evanescent plane waves have been removed. Gaussian beams observed in nature should show some evidence of the associated anomalies, even if the beam is almost collimated.     

Stabilizing the intensity of a wave amplified by a beam of particles

The intensity of an electromagnetic wave interacting self-consistently with a beam of charged particles as in a free electron laser, displays large oscillations due to an aggregate of particles, called the macro-particle. In this article, we propose a strategy to stabilize the intensity by re-shaping the macro-particle. This strategy involves the study of the linear stability (using the residue method) of selected periodic orbits of a mean-field model. As parameters of an additional perturbation are varied, bifurcations occur in the system which have drastic effect on the modification of the self-consistent dynamics, and in particular, of the macro-particle. We show how to obtain an appropriate tuning of the parameters which is able to strongly decrease the oscillations of the intensity without reducing its mean-value.     

Evaluation and preliminary measurement of the interaction of a dynamical gravitational near field with a cryogenic gravitational wave antenna

We present a detailed analysis of the effect of the gravitational field generated by a small rotating quadrupole on a graviational wave antenna and we report on the preliminary measurement of this effect on the Explorer 2270 kg cryogenic gravitational wave antenna of the Rome group. The induced signal had an amplitude twenty times larger than the detector noise when the antenna was equipped with an FET amplifier and was easily detected without requiring integration in time. We remark that with this method we were able to make an absolute calibration of a gravitational wave antenna.     

The measurement of bending wave intensity in a two-dimensional structure

I.IntroductionOfallstructuralwaves,bendingwaveismostimportant.Itiseasilyexcitedandresultsinairbornenoiseradiation'Inpractice,itisnecessarytodeterminetheenergydistributionandpowertransmissionincoupledstructl1res.Bendingwaveenergycanbecalculatedfrombendingwaveaccelerationwhilebendingwavepowertransmissionischaracterizedbybendingwaveintensitywhichisavectorgivillgthemagnitudeanddirection.TheengineeringaPplicationofthevectorpropertyofbendingwaveilltensityisnumerous[1~3]buttheinvestigationinitispre…     

Propagation of a beam of gamma rays in the field of a monochromatic laser wave

The head-on propagation of a beam of γ grays through the field of a laser wave is investigated. The optical properties of the laser wave (as a medium) are described by the dielectric tensor. The refractive indices are determined, and the polarization characteristics of electromagnetic normal modes capable of propagating in such a medium are investigated. Relations are derived to describe the variation of the initial polarization and intensity of a γ-ray beam as it propagates in a laser field. The influence of laser intensity on the investigated process is discussed. Zh. éksp. Teor. Fiz. 112, 2016–2029 (December 1997)     

Quasi-stationary stage of a nonequilibrium optical discharge in the field of a Bessel wave beam

The self-consistent stationary distributions of the field and plasma produced by Bessel wave beams in a gas with the ionization and Kerr nonlinearities are studied analytically. Using a stationary model based on the condition of a constant field amplitude in the ionized region, the structures are considered to be formed by Bessel beams of two types: with an azimuthal electric field equal to zero at the symmetry axis and a quasitrans-verse field having a maximum at the axis. A specific feature of the plasma channel formed in the first case is the presence of a nonionized region in its central part (tubular discharge), whose radius is independent of the incident power. In the second case, the channel is continuous. The relation is found between the incident radiation power and the external radius of the discharge. It is shown that the Kerr nonlinearity, which is especially important at small divergence angles of the beam, enhances the maximum plasma density and reduces the discharge radius. The parameters of plasma structures produced upon focusing a Gaussian beam by a conical lens are estimated using the model proposed.     

Collective bubble dynamics near a surface in a weak acoustic standing wave field

The transport of bubbles to a neighboring surface is very important in surface chemistry, bioengineering, and ultrasonic cleaning, etc. This paper proposes a multi-bubble transport method by using an acoustic standing wave field and establishes a model that explains the multi-bubble translation by expressing the balance between Bjerknes forces and hydrodynamic forces on a bubble in a liquid medium. Results indicated that the influence of primary Bjerknes force, secondary Bjerknes force, and buoyancy force on the bubble translation depends on the position of the target bubble in the acoustic field. Moreover, it was found that increasing the size of a bubble or pressure amplitude can accelerate the bubble motion and enhance the bubble-bubble interaction. The secondary Bjerknes force between two bubbles can switch from an attractive one when they oscillate in phase to a repulsive one when the bubble oscillations are out of phase. These findings provide an insight into the multi-bubble translation near a surface and can be applied to future bubble motion control studies, especially in drug delivery, sonoporation, and ultrasonic cleaning.     

近简并四波混频相位共轭介质中的光强分布

从求解耦合波方程出发，详细研究了非线性光学介质中由近简并四波混频所产生的相位共轭过程。以上述波方程的解为基础，给出作为混频结果的反射传播相位共轭波沿介质轴向的光强分布，得到比以往文献中所报道的更为精确的结果，从而为选择工作物质的最佳尺寸提供了理论依据。     

Cyclotron damping of the space charge wave of a beam in a nonuniform magnetic field region

The space charge wave of an electron beam excited by the reactive medium instability in a uniform magnetic field region is observed to propagate into the region of increasing magnetic field. When the wave passes through the cyclotron resonance region, it suffers heavy cyclotron damping.     

Dynamics of a charged particle in the presence of both a quasimonochromatic wave and a strong magnetic field

A multiple-frequency system of equations is averaged to obtain the relativistic equations of motion for a charged particle in the field of a quasimonochromatic wave propagating along a strong magnetic field.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 70–72, December, 1976.We wish to thank L. M. Gorbunov for valuable discussions.     

Self-action of a light beam in nematic liquid crystals in the presence of a DC electric field

The results of experimental study of the light beam self-action in a nematic liquid crystal placed in a dc electric field are presented, and a theory of this effect is developed. This self-action of a light beam is shown to cause a hyperbolic umbilic caustic. The intensity distribution and caustics calculated in the far diffraction zone of the light beam agree well with the experimental data.