Evolution Of Beam Research Articles

A thermo-elasto-plastic model for a fiber-metal laminated beam with interfacial damage

In this paper, a thermo-elasto-plastic model for the fiber-metal laminated (FML) beams is established and the mechanic characterization of a FML beam with interfacial damage under thermal environment is investigated. The elasto-plastic behavior of the FML beam is modeled by a macromechanical orthotropic plasticity theory, where the composite layers in the FML are assumed to be linearly elastic and the aluminum layers are taken as orthotropic elasto-plastic. Additionally, the thermal stresses in the FML beam are studied by introducing heat conduction equation. Considering the mismatch in properties of different layers, the interfacial damage is investigated based on cohesive zone model and shear-lag model, and the evolution of the interfacial damage is addressed as well. The incremental thermo-elasto-plastic governing equations for the FML beams are solved by finite difference method and iteration method. In the numerical simulations, the temperature variation, the elasto-plastic deformation and the interfacial damage evolution of the elasto-plastic FML beam are discussed in detail. The results show that mode II interfacial damage occurs at 1/4 and 3/4 length of the beam and mode I damage is most likely to happen at the center.

Power scale-up and propagation evolution of structured laser beams concentrated on 3D Lissajous parametric surfaces

We systematically explore the power scale-up and propagation evolution of Lissajous structured beams in a lowly Nd-doped YVO4 laser with the off-axis pumping scheme. We experimentally found that the average output power can be up to 1.0 W for the output transmission in the range of 1.8–10% at an incident pump power of 6.2 W. It is also found that when the output transmission is greater than 5%, the spatial coherence is considerably reduced to lead to a feature of broken Lissajous figures in transverse patterns. Moreover, transverse patterns varying with propagation direction are remarkably measured to manifest the 3D characteristics of Lissajous structured beams. We also employ the formula of coherent states to make a comparison with experimental observations and to reveal the transverse momentum density varying with propagation direction.

Propagation evolution of an off-axis high-order cylindrical vector beam.

The propagation characteristics of an off-axis high-order cylindrical vector beam (OHCVB) are studied in this paper. The analytic expressions for the electric field and intensity distribution of the OHCVB propagating in free space are presented, to our knowledge for the first time. The transverse intensity of the OHCVB, different from that of the input Gaussian beam, does not have an axially symmetric distribution, owing to a slight dislocation between the polarization singularity located in the vector field generator and the center point of the Gaussian beam. Numerical results show that the intensity distribution during propagation strongly depends on the propagation distance, dislocation displacement, and topological charge. Accompanied by beam expansion, the intensity distribution of the OHCVB tends to eventually become steady, and the dark core of the vector beam will disappear gradually during the process of propagation. Moreover, with the increase of the topological charge, more energy will be transferred from the x axis to the y axis, and the annular intensity is split into two parts along the y-axis direction. The results help us to investigate the dynamic propagation behaviors of the HCVB under the off-axis condition and also guide the calibration of the off-axis high-order cylindrical vector field in practice.

A tolerance analysis on design parameters of parabolic and hyperbolic secant active GRIN materials for laser beam shaping purposes

The present paper considers two gain GRIN media, characterized by a complex parabolic and hyperbolic secant refractive index profile, for the design of uniform beam shaper systems. A general condition for beam shaping is obtained from the equation describing the evolution of the half-width of a plane Gaussian beam in the GRIN media. The simulation of the irradiance evolution of an input plane Gaussian beam—operating at 575 nm and beam waist radius of 0.45 mm—in each material is shown, in order to examine the beam shaping quality in terms of thickness of the active GRIN media and input beam wavelength.

Evolution of an Airy beam in a saturated medium

The nonlinear dynamics of an Airy beam in a saturated medium is presented. An analytical expression for the evolution of the Airy beam width in the root-mean-square sense is derived. The novel features of the collapsing beams of an Airy beam in a saturated medium are demonstrated by numerical calculation. These collapsing beams shift laterally and are the main property of the Airy beam. However, the collapsing beam in the major lobe of an Airy beam tends to shift in the opposite direction for conservation of the beam centroid. The location and evolution of the collapsing beams depend strongly on the initial powers. The peak intensities of the collapsing beams oscillate at almost the same intensity in the saturated medium, regardless of their initial powers. These results are useful for manipulating nonlinear wave collapse and multi-filamentation.

Electron-beam dynamics in a strong laser field including quantum radiation reaction

The evolution of an electron beam colliding head-on with a strong plane-wave field is investigated in the framework of strong-field QED including radiation-reaction effects due to photon emission. Employing a kinetic approach to describe the electron and the photon distribution it is shown that at a given total laser fluence the final electron distribution depends on the shape of the laser envelope and on the pulse duration, in contrast to the classical predictions of radiation reaction based on the Landau-Lifshitz equation. Finally, it is investigated how the pair-creation process leads to a nonlinear coupled evolution of the electrons in the beam, of the produced charged particles, and of the emitted photons.

HiPACE: a quasi-static particle-in-cell code

We introduce the Highly efficient Plasma Accelerator Emulation (HiPACE) code. It is a relativistic, electromagnetic, three-dimensional and fully parallelized particle-in-cell (PIC) code and uses the quasi-static approximation to efficiently simulate a variety of beam-driven plasma-wakefield acceleration scenarios. HiPACE exploits the disparity of time scales in the interaction of highly relativistic particle beams with plasma to decouple beam and plasma evolution. This enables time steps which are many times greater than those used in full PIC codes. Comparisons to the fully explicit PIC code OSIRIS show the capability of the quasi-static PIC code to consistently simulate problems in beam-driven plasma acceleration while reducing the required number of core hours by orders of magnitude. This work outlines the physical basis, describes the numerical implementation and assesses the parallel performance of the code which in combination lead to high computational efficiency.

Optical surface waves supported by the interface between a metal and a biased centrosymmetric photorefractive crystal

We show that the optical beam evolution equations at the interface between a metal and a biased centrosymmetric photorefractive (CP) crystal can exhibit delocalized surface waves, shock surface waves, and localized surface waves (LSWs). Only LSWs have not oscillating tails in the volume of the CP crystal. For a given value of the propagation constant b, the transverse width and energy of LSWs increases with the order of LSWs. For a given order of LSWs, the energy of LSWs decreases with an increase in |b|, the transverse width of LSWs increases with |b| when |b| is less than the absolute value of a certain threshold bct and decreases with an increase in |b| when |b|>|bct|. The stability properties of these LSWs are also discussed in detail.

Size evolution of ion beam synthesized Pb nanoparticles in Al.

The size evolution of Pb nanoparticles (NPs) synthesized by ion implantation in an epitaxial Al film has been experimentally investigated. The average radius R of Pb NPs was determined as a function of implantation fluence f. The R(f) data were analyzed using various growth models. Our observations suggest that the size evolution of Pb NPs is controlled by the diffusion-limited growth kinetics (R2∝f). With increasing implantation current density, the diffusion coefficient of Pb atoms in Al is evident to be enhanced. By a comparative analysis of the R(f) data, values of the diffusion coefficient of Pb in Al were obtained.

Transverse evolution of a long relativistic electron beam governed by the Vlasov-Poisson-type pair of equations within the plasma wake field dynamics in the local regime

An analysis of the transverse plasma wake field dynamics excited by a long relativistic electron beam is carried out in a purely local regime, in which the transverse beam spot-size is much bigger than the plasma wavelength. This is done by using the Vlasov equation, that governs the kinetic spatiotemporal evolution of the transverse paraxial beam transport. A self-consistent description of the beam dynamics is then provided by coupling the Vlasov equation with a Poisson-type equation. Furthermore, the latter relates the beam density with the plasma wake potential energy. Remarkably, the approach here proposed seems to be suitable for describing the beam self-modulation and the prediction of the beam collapse.

Application of Lie transform techniques for simulation of a charged particle beam

We study a Lie Transform method for a charged beam underthe action of a radial external electric field. The aim of the Lie transform method that is used here is to construct a change of variable which transforms the 2D kinetic problem into a 1D problem. This reduces the dimensionality of the problem and make it easier to solve numerically.After applying the Lie transform method, we truncate the expression of the characteristics of the Vlasov equation and the expression of the Poisson equation in the Lie coordinate system and we develop a numerical method for solving the truncated model and we study its efficiency for the simulation of long time beam evolution.

Evolution of ion beam induced patterns on Si(001)

In the range of incidence angles between 58${}^{\ensuremath{\circ}}$ and 79${}^{\ensuremath{\circ}}$, Si develops erosion patterns through room-temperature exposure to 2 keV ${\text{Kr}}^{+}$, while for other incidence angles it remains flat. We investigate the formation of these patterns through all in situ sample preparation and investigation under ultrahigh vacuum conditions. The ion fluence is varied by a factor of 1000 for the incidence angles of 63${}^{\ensuremath{\circ}}$ and 75${}^{\ensuremath{\circ}}$. The resulting morphologies are imaged by scanning tunneling microscopy and quantitatively analyzed in view of roughness, wavelength, disorder, and surface slopes. We find it necessary to distinguish between low-fluence and high-fluence regimes of pattern formation. While in both low-fluence regimes a similar parallel mode ripple pattern evolves, the high-fluence regimes are distinctly different and evidence either the evolution of disordered perpendicular ripples or a roof-tile structure for 63${}^{\ensuremath{\circ}}$ or 75${}^{\ensuremath{\circ}}$, respectively. The data are compared to other experimental data for ion beam erosion of Si and Ge enabling us to assess the universality of our observations. Comparison to existing models for the surface evolution under ion exposure allows us to draw conclusions on the applicability of these models for pattern formation on Si(001).

RELATIVISTIC PAIR BEAMS FROM TeV BLAZARS: A SOURCE OF REPROCESSED GeV EMISSION RATHER THAN INTERGALACTIC HEATING

The interaction of TeV photons from blazars with the extragalactic background light produces a relativistic beam of electron-positron pairs streaming through the intergalactic medium (IGM). The fate of the beam energy is uncertain. By means of two- and three-dimensional particle-in-cell simulations, we study the non-linear evolution of dilute ultra-relativistic pair beams propagating through the IGM. We explore a wide range of beam Lorentz factors gamma_b>>1 and beam-to-plasma density ratios alpha<<1, so that our results can be extrapolated to the extreme parameters of blazar-induced beams (gamma_b~10^6 and alpha~10^(-15), for the most powerful blazars). For cold beams, we show that the oblique instability governs the early stages of evolution, but its exponential growth terminates - due to self-heating of the beam in the transverse direction - when only a negligible fraction ~(alpha/gamma_b)^(1/3)~10^(-7) of the beam energy has been transferred to the IGM plasma. Further relaxation of the beam proceeds through quasi-longitudinal modes, until the momentum dispersion in the direction of propagation saturates at DeltaP_{b,parallel}/gamma_b m_e c ~ 0.2. This corresponds to a fraction ~10% of the beam energy being ultimately transferred to the IGM plasma, irrespective of gamma_b or alpha. If the initial dispersion in beam momentum satisfies DeltaP_{b,parallel}/gamma_b m_e c > 0.2 (as typically expected for blazar-induced beams), the fraction of beam energy deposited into the IGM is much smaller than ~10%. It follows that at least ~90% of the beam energy is still available to power the GeV emission produced by inverse Compton up-scattering of the Cosmic Microwave Background by the beam pairs.

Initiating self-focusing of beams carrying spatial phase singularities

In this work, we show both experimentally and by numerical simulations that the presence and evolution of a ring dark beam and/or an on-axis optical vortex nested on a bright background beam noticeably perturb the host background. In a photorefractive nonlinear medium (crystal SBN) these perturbations can initiate self-focusing of the background. By changing the dark ring radius and the presence of an optical vortex and keeping all other experimental parameters unchanged, we can control the dynamics at the initial stage of longitudinal self-focusing and the type of self-focusing structure (single peak or bright ring of variable radius). The presented results may appear especially important in experiments that involve cascaded nonlinear frequency mixing of singular beams, in which accelerated dark beam spreading is accompanied by self-focusing of certain portions of the perturbed host beam.

Propagation dynamic of a Gaussian in the inverted nonlinear photonic crystals

In this work, we study the evolution of a Gaussian beam inside a one-dimensional inverted nonlinear photonic crystals (INPC) with a Kerr nonlinearity. The INPC is a kind of virtual crystals which is generated by the optical induction via the electromagnetically induced transparency (EIT). The propagation dynamics of the Gaussian with different total power are identified. Four types of propagation behavior are found. They are collapse beam, breather beam, soliton and symmetry-breaking beam, respectively. The border between these four behavior types are given. For symmetry-breaking beam, an asymmetric profile of the beam is evolving from the symmetry Gaussian, which can be termed as a kind of dynamical symmetry breaking (DSB). The influences on the appearance of the symmetry breaking point are studied by varying input parameters of the Gaussian. The results of this work are both suitable in nonlinear optics and Bose-Einstein condensate (BEC).

Exact cascading nonlinearity in quasi-phase-matched quadratic media.

The evolution of light pulses and beams in a quasi-phase-matched (QPM) quadratic medium is usually described by considering only the spatial harmonic of the QPM grating that minimizes the residual phase-mismatch. I show that, for strongly phase-mismatched interactions (the cascading regime), several harmonics need to be accounted for in order to obtain the correct value of the effective cubic nonlinearity, for which I find a simple analytical expression. I discuss the effects of the higher order harmonics of the grating on solitary wave propagation.

Propagation of nonlinear sound beams in marine sediments

Parametric arrays are recently considered as directional sound sources for locating buried objects in marine sediments. To understand how nonlinear sound beams generated by parametric arrays propagate in marine sediments, a theoretical framework that accounts for the combined effects of diffraction, absorption, nonlinearity, and the physics of sediment is necessary. In this paper, the KZK equation is extended to augment a number of well-known sediment models. Nonlinear evolution of sound beams are computed and compared under different sediment models, namely, the fluid model, Buckingham's grain-shearing model, the Biot-Stoll model, and the effective density fluid model (EDFM). [This work was conducted in the Unmanned Technology Research Center (UTRC) sponsored by the Defense Acquisition Program Administration (DAPA) and the Agency for Defense Development (ADD) in the Republic of Korea.]

Transverse energy circulation and the edge diffraction of an optical vortex beam.

Edge diffraction of a circular Laguerre-Gaussian beam represents an example of the optical vortex symmetry breakdown in which the hidden "vortex" energy circulation is partially transformed into the visible "asymmetry" form. The diffracted beam evolution is studied in terms of the irradiance moments and the moment-based parameters. In spite of the limited applicability of the moment-based formalism, we show that the "vortex" and "asymmetry" parts of the orbital angular momentum can still be reasonably defined for the hard-edge diffracted beams and retain their physical role of quantifying the corresponding forms of the transverse energy circulation.

Feature-Based Analysis of Plasma-Based Particle Acceleration Data

Plasma-based particle accelerators can produce and sustain thousands of times stronger acceleration fields than conventional particle accelerators, providing a potential solution to the problem of the growing size and cost of conventional particle accelerators. To facilitate scientific knowledge discovery from the ever growing collections of accelerator simulation data generated by accelerator physicists to investigate next-generation plasma-based particle accelerator designs, we describe a novel approach for automatic detection and classification of particle beams and beam substructures due to temporal differences in the acceleration process, here called acceleration features. The automatic feature detection in combination with a novel visualization tool for fast, intuitive, query-based exploration of acceleration features enables an effective top-down data exploration process, starting from a high-level, feature-based view down to the level of individual particles. We describe the application of our analysis in practice to analyze simulations of single pulse and dual and triple colliding pulse accelerator designs, and to study the formation and evolution of particle beams, to compare substructures of a beam, and to investigate transverse particle loss.

Gaussian beam evolution in nonlinear inhomogeneous plasma

AbstractThe method of nonlinear complex geometrical optics (NCGO) is proposed in this paper for description of the evolution of a spatially narrow Gaussian beam (GB) in an inhomogeneous nonlinear plasma. NCGO method deals with first-order ordinary differential equations for the complex curvature of the wave front and for GB amplitude and for second-order ordinary differential equation for GB width. Thus, NCGO simplifies the description of GB diffraction and self-focusing effects as compared to the known methods of plasma physics and this way it can be assumed to be attractive and comprehensive approach in problems of plasma heating by electromagnetic waves. Moreover, we demonstrate in this paper some regularity for nonlinear inhomogeneous plasma in the framework of which central ray of a GB is not subjected to nonlinear refraction within NCGO method boundary applicability. On the contrary, the beam width, wave front curvature, and GB amplitude are modified by diffraction and self-focusing processes. General properties of the beam propagation are illustrated with results of numerical modeling for two particular cases: GB diffraction and self-focusing along curvilinear trajectory with torsion in axially symmetric plasma column and GB reflection from nonlinear inhomogeneous plasma layer. We prove in this paper that NCGO is new effective method of plasma physics, which can be applied for improvement of ray tracing techniques and plasma diagnostics.