Bending wave intensity in a thick beam

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

A beam interpolation algorithm in digital multi-beam sonar

I.IntroductionThedigita1operationins0narsystembringsagreatadvantageinbeamforming.Itispos-sib1etorealizesomcalg0rithmsindigita1technique,whichisusua11yhardtoorimpossib1etoAnp1ementintraditiona1ana1ogues0nar.Asanexamp1e,ageometrygraphofcirclearrayisil-1ustratedinFig,1.Thetotalnumber0farraye1ementisN.Therearetwokindsofbeam.TheA-c1assbeamconsistsof2M-le1ements,thesteeringdirectionisjustlocatedintheposi-honofoneofthearrayelement;TheB-classbeamconsistsof2Me1ementsandthesteeringdirectionisinthem…     

Electron acceleration in a tightly focused laser beam

Electron acceleration in a tightly focused ultra-intensity linear polarized laser beam is investigated numerically. It has been found that the acceleration is strong phase dependent and is periodic to the variety of the initial laser field phase. When optimal initial parameters are chosen, the electron can be accelerated effectively. The accelerated electrons are emitted in pulses of which the full width is less than the half period of the laser field.     

Simulation of beam gas coulomb scattering in HALS

In conventional research on beam gas coulomb scattering(BGCS), only the related beam lifetime using the analytical method is studied. In this paper, using the particle-in-cell Monte Carlo collisions(PIC-MCC) method,we not only simulated the beam lifetime but also explored the effect of BGCS on the beam distribution. In order to better estimate the effect on particle distribution, we study the ultra-low emittance electron beam. Here we choose the He Fei Advanced Light Source. By counting the lost particles in a certain time, the corresponding beam lifetime we simulated is 4.8482 h/13.8492 h in x/y, which is very close to the theoretic value(5.0555 h /13.7024 h in x/y).By counting the lost particles relative to the collided particles, the simulated value of the loss probability of collided particles is 1.3431e-04, which is also very close to the theoretical value(1.3824e-04). Besides, the simulation shows there is a tail in the transverse distribution due to the BGCS. The close match of the simulation with the theoretic value in beam lifetime and loss probability indicates our simulation is reliable.     

Self-focusing of acoustical beam in solid by time-reversal processing

1 IntroductionTime reversal is a unique self-adaptive focusing technique, it can realize the acollsticalbeam focusing and ultrasonic testing in the inhomogeneous mediatl], and the inhomogeneityof the media always causes curve of sound ray, distortion of wavefront, aberrance and blur ofimage. It is difficult or impossible to know the acoustical inhomogeneity of the media, such asocean or interior of solid. The greatest advantage of TR is that it can realize the self-adaptivefocusing without pr…     

Propagation of an Airy–Gaussian beam in uniaxial crystals

Under the paraxial approximation, the analytical propagation expression of an Airy–Gaussian beam(Ai GB) in uniaxial crystals orthogonal to the optical axis is investigated. The propagation dynamics of the Ai GB is given for different ratios of the extraordinary index to the ordinary refractive index. It has been found that the continuity and the self-bending effect of Ai GB become weaker when the ratio increases. From the figure of the maximum intensity of Ai GB, one can see that the maximum intensity is not monotone decreasing due to the anisotropic effect of the crystals. The intensity distribution of Ai GB in different distribution factors is shown. The Ai GB converges toward a Gaussian beam as the distribution factor increases.     

Partially coherent elegant Hermite–Gaussian beam in turbulent atmosphere

Based on the extended Huygens–Fresnel integral, analytical formulas for the cross-spectral density, mean-squared beam width and angular spread of a partially coherent elegant Hermite–Gaussian (HG) beam in turbulent atmosphere are derived. The evolution properties of the average intensity, spreading and directionality of a partially coherent elegant HG beam in turbulent atmosphere are studied numerically. It is found that the partially coherent elegant HG beam with smaller initial coherence width, larger beam order and longer wavelength is less affected by the atmospheric turbulence. Compared to the partially coherent standard HG beam, the partially coherent elegant HG beam is less affected by turbulence under the same condition. Furthermore, it is found that there exist equivalent partially coherent standard and elegant HG beams, equivalent fully coherent standard and elegant HG beams, and an equivalent Gaussian–Schell-model beam may have the same directionality as a fully coherent Gaussian beam whether in free space or in turbulent atmosphere. Our results can be utilized in short and long atmospheric optical communication systems.     

Fast electron beam–plasma interaction in single-walled carbon nanotubes

A theoretical study on the plasmon-polariton modes coupled with a fast electron beam inside a metallic single-walled carbon nanotube is presented. The Maxwell’s equations coupled with a linearized hydrodynamic model for the nanotube’s charge oscillations are used. By considering the electron beam effects, general expression of dispersion relation of electromagnetic modes on nanotube’s surface is obtained. It is shown numerically that by considering the electron beam effects, the polariton frequency shifts to lower values.     

A novel beam–spin asymmetry in double-hadron inclusive lepto-production

We show that a new beam–spin asymmetry appears in deep inelastic inclusive lepto-production at low transverse momenta when a hadron in the target fragmentation region is observed in association with another hadron in the current fragmentation region. The beam leptons are longitudinally polarized while the target nucleons are unpolarized. This asymmetry is a leading-twist effect generated by the correlation between the transverse momentum of quarks and the transverse momentum of the hadron emitted by the target. Experimental signatures of this effect are discussed.     

On the influence of the electron-velocity spread in a beam on the mechanism of Cherenkov beam–plasma interaction

The instability of an electron beam in cold plasma is considered in the linear potential approximation with different velocity-distribution functions of beam electrons. It is demonstrated that the mechanism of beam instability in plasma changes as the electron-velocity spread is increased: the hydrodynamic single-particle instability mode evolves into the hydrodynamic collective mode or the single-particle kinetic one. Instability growth rates in different modes are determined analytically and numerically.     

Measurement of the beam asymmetry in η photoproduction off the proton

The beam asymmetry, Σ , was measured at ELSA in the reaction p → ηp using linearly polarised tagged photon beams, produced by coherent bremsstrahlung off a diamond. The crystal was oriented to provide polarised photons in the energy range E _γ = 800 to 1400MeV with the maximum polarisation of P _γ = 49 % obtained at 1305MeV. Both dominant decay modes of the η into two photons and 3π⁰ were used to extract the beam asymmetry from the azimuthal modulation of the cross-section. The measurements cover the angular range Θ_cm ≃ 50 -150 degrees. Large asymmetries up to 80% are observed, in agreement with a previous measurement. The eta-MAID model and the Bonn-Gatchina partial wave analysis describe the measurements, but the required partial waves differ significantly.     

Diffraction of a modulated laser beam in 3ω optics system

Based on diffraction optical theory, diffraction of a laser beam with periodic amplitude modulation and phase distortion is derived in 3ω optics system. Influence of defocus distance and focal length of a focusing lens on intensity distribution of diffraction light is investigated by numerical simulation. The results show that appropriate distance away from the focus spot and increase the focal length in final optical systems are beneficial to control the modulation of light intensity fluctuations and reduce the optical components damage caused by small-scale self-focusing effect.     

Role of beam propagation in Goos-Hänchen and Imbert-Fedorov shifts

We derive the polarization-dependent displacements parallel and perpendicular to the plane of incidence for a Gaussian light beam reflected from a planar interface, taking into account the propagation of the beam. Using a classical-optics formalism we show that beam propagation may greatly affect both Goos-H?nchen and Imbert-Fedorov shifts when the incident beam is focused.     

Propagation characteristics of a high-power beam in weakly relativistic-ponderomotive thermal quantum plasma

The present work explores the propagation characteristics of high-power beams in weakly relativistic-ponderomotive thermal quantum plasma. A q-Gaussian laser beam is taken in the present investigation. The quasi-optics equation obtained in the present study is solved through a well-established Wentzel–Kramers–Brillouin approximation and paraxial theory approach for obtaining the second-order differential equation describing the behavior of beam width of the laser beam. Further, a numerical simul...     

Slant path average intensity of finite optical beam propagating in turbulent atmosphere

The average intensity of finite laser beam propagating through turbulent atmosphere is calculated from the extended Huygens Presnel principle. Formulas are presented for the slant path average intensity from an arbitrarily truncated Gaussian beam. The new expressions are derived from the modified von Karman spectrum for refractive-index fluctuations, quadratic approximation of the structure function, and Gaussian approximation for the product of Gaussian function and Bessel function. It is shown that the form of average intensity is not a Gaussian function but a polynomial of the power of the binomial function, Gaussian function, and the incomplete gamma function. The results also show that the mean irradiance of a finite optical beam propagating in slant path turbulent atmosphere not only depends on the effective beam radius at the transmitting aperture plane, propagation distance, and long-term lateral coherence length of spherical wave, but also on the radius of emit aperture.     

Propagation of a beam halo in accelerator test facility 2 at KEK

The beam halo is a major issue for interaction region (IR) backgrounds at many colliders, for example, future linear colliders, B factories, and also it is an important problem at ATF2. In this paper, we report on the halo propagation along the ATF2 beam line with realistic apertures, the nonlinear optics influence on the increasing number of halo particles input is analyzed, and the transmitted halo particles distribution just before the last BPM is then described, the results from which will benefit the Compton recoil electrons measurement.     

Laser beam defocusing at 1.06 μm by carrier excitation in silicon

Laser beams from a 15 ns pulsed Nd: YAG laser are defocused after passing silicon crystals with 400 m thickness. The beam profile changes into a ring structure at incident laser energies up to 30 mJ and energy densities of 440 mJ/cm². The experimental deflection angles agree with calculations assuming refractive index changes due to electronhole pairs produced by interband absorption.     

Regimes and spectra of čerenkov beam instability in a nonlinear plasma

We study the nonlinear evolution of an arbitrary initial disturbance due to the development of Čerenkov beam instability in a magnetized plasma-beam system of finite transverse size. Singleparticle, collective, and aperiodic regimes of this instability are considered. We calculate the nonlinear spatial spectra of the waves excited at different development stages of the beam instability in a plasma for the cases of quasi-monochromatic, pulsed, and noise initial disturbances. We analyze the formation and decay of regular structures in the beam and plasma at the developed nonlinear stage of the process. We find that plasma nonlinearity leads to the transfer of disturbance energy to the short-wave region of the spectrum. We show that, due to the development of beam instability, noise initial disturbance tends to become more monochromatic, whereas the shape of a pulsed one tends to remain unchanged. Transformation of monochromatic spatial disturbances into quasi-monochromatic plasma waves due to the instability development is analyzed. Institute of General Physics of the Russian Academy of Sciences, Moscow, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 10, pp. 958–976, October 1999.     

Propagation of cosh Gaussian laser beam in plasma with density ripple in relativistic – ponderomotive regime

Self-focusing of cosh Gaussian laser beam in plasma with periodic density ripple has been investigated. The pondermotive force on electron and the relativistic oscillation of the electron mass causes periodic self-focusing/defocusing of the cosh Gaussian laser beam. The beam converges in the region of high plasma density due to dominance of self-focusing effect over diffraction effect and diverges in the low density region. Non-linear partial differential equation governing the evolution of complex envelope in slowly varying approximation is solved using paraxial ray approximation. The variation of beam-width parameter is studied with distance of propagation for different values of ripple wave number d and decentred parameter b. In order to get strong self-focusing, wavelength and intensity parameters of cosh Gaussian laser beam are optimized.