Evolution Of Beam Research Articles

Propagation characteristics of cosine-Gauss beams in nonlinear Schrödinger equation with nonlocal nonlinearity

The evolution of cosine-Gauss beams in nonlocal optical medium which can be governed by the nonlinear Schrödinger equation with nonlocal nonlinearity is investigated. A set of mathematical analytical expressions describing propagation characteristics are derived, and the numerical simulation results and illustrations of typical propagation characteristics are given. The results show that the cosine-Gauss beam has a variety of light intensity distribution forms at the initial position and changes periodically in the propagation process. There are different propagation characteristics under different initial parameters of cosine-Gauss beams. If the cosine-Gauss beam is incident at the on-waist position, it can form a generalized soliton form, that is, the statistical transverse width of cosine-Gauss beams changes and the optical intensity distribution changes with a period; also, a generalized breathers can be formed, that is, the statistical transverse width and optical intensity distribution change with a period. If the cosine-Gauss beam is incident on the off-waist position, it only exist in the form of generalized breather and cannot form generalized soliton. The physical explanation is given.

Self-healing of the bored helico-conical beam.

We investigate the dynamic evolution and self-healing properties of the bored helico-conical beams with different filter parameter S in this paper. The relative error coefficient, D, is utilized to judge the self-healing effect of the bored helico-conical beam. The result demonstrates that the self-healing effect of the bored beams will be perfect when D approaches to 0. We also discuss the influence of the filter parameter S on the effective self-healing distance theoretically and experimentally. The result demonstrates that the effective self-healing distance decreases exponentially with the increasing filter parameter S. Moreover, the corresponding transverse energy flows of the bored beams are analyzed. The experimental results of the dynamic evolution for the bored helico-conical beams agree with the simulation ones well.

Self-rotating beam in the free space propagation.

We introduce a class of self-rotating beams whose intensity profile tends to self-rotate and self-bend in the free space propagation. The feature of the self-rotating beams is acceleration in the three-dimensional (3D) space. The acceleration dynamics of the self-rotating beams is controllable. Furthermore, multiple self-rotating beams can be generated by a combined diffractive optical element (DOE) simultaneously. Such a beam can be viewed as evolution of a vortex beam by changing the exponential constant of phase. We have generated this beam successfully in the experiment and observed the expected phenomenon, which is basically consistent with the result of the numerical simulation. Our results may provide new insight into the self-rotating beam and extend potential applications in optical imaging.

Evolution properties of vortex beams through strongly nonlocal nonlinear media

The evolution properties of a vortex Hermite cosine-hyperbolic-Gaussian beam (vHChGB) propagating in a strongly nonlocal nonlinear media (SNNM) are examined theoretically based on the Snyder-Mitchell model. Mathematical and numerical calculations are performed to illustrate the propagation formula, the second-order intensity moment beam width and the curvature radius of an on-waist incident vHChGB in SNNM. The results reveal that under general conditions, the vHChGB evolves periodically upon propagation in SNNM, and the beam shape is strongly dependent on the power and the parameters of the incident beam. The beam evolution during propagation is generally breather-like, and when the incident beam power equals to the critical power value, the beam behaves like a soliton. The evolution behaviors of vHChGB in SNNM are well demonstrated, which could have promising applications in optical switch and micro-manipulations.

Evolution properties of twisted Hermite Gaussian Schell-model beams in non-Kolmogorov turbulence

A general form of twisted Hermite Gaussian Schell-model (THGSM) beams is introduced; analytical expressionsare obtained for cross-spectral density and M2-factor using the extended Huygens-Fresnel principle and Wigner function. The evolution of THGSM beams during propagation in non-Kolmogorov turbulence is shown numerically; the beams exhibit self-splitting and twist into two lobes. The intensity distribution evolves into a Gaussian shape and beam quality worsens with increasing distance; the intensity distribution and M2-factor are determined by the twist factor, beam orders, and other beam parameters. THGSM beams provide more degrees of freedom to regulate beam parameters, thereby enriching the types of partially coherent beams.

Multi-layer structure formation of relativistic electron beams in plasmas

A two-dimensional electromagnetic particle-in-cell simulation model is proposed to study the density evolution and collective stopping of electron beams in background plasmas. We show here the formation of the multi-layer structure of the relativistic electron beam in the plasma due to the different betatron frequency from the beam front to the beam tail. Meanwhile, the nonuniformity of the longitudinal wakefield is the essential reason for the multi-layer structure formation in beam phase space. The influences of beam parameters (beam radius and transverse density profile) on the formation of the multi-layer structure and collective stopping in background plasmas are also considered.

Effect of Aluminum on Microstructural Evolution and Mechanical Properties of Laser Beam Welded Alxcocrfeni High Entropy Alloys

Effect of Aluminum on Microstructural Evolution and Mechanical Properties of Laser Beam Welded Alxcocrfeni High Entropy Alloys

Evolution of Copper Step Beams During Graphene Growth by Cvd Method

Evolution of Copper Step Beams During Graphene Growth by Cvd Method

Mapping non-laminar proton acceleration in laser-driven target normal sheath field

Abstract We report on experimental observation of non-laminar proton acceleration modulated by a strong magnetic field in laser irradiating micrometer aluminum targets. The results illustrate the coexistence of ring-like and filamentation structures. We implement the knife edge method into the radiochromic film detector to map the accelerated beams, measuring a source size of 30–110 μm for protons of more than 5 MeV. The diagnosis reveals that the ring-like profile originates from low-energy protons far off the axis whereas the filamentation is from the near-axis high-energy protons, exhibiting non-laminar features. Particle-in-cell simulations reproduced the experimental results, showing that the short-term magnetic turbulence via Weibel instability and the long-term quasi-static annular magnetic field by the streaming electric current account for the measured beam profile. Our work provides direct mapping of laser-driven proton sources in the space-energy domain and reveals the non-laminar beam evolution at featured time scales.

Propagation and transformation properties of rotating sinh-Gaussian beam in nonlinear media with spatial nonlocality

In this paper, by introducing a rotating coordinate system, the evolution and propagation of astigmatic sinh-Gaussian beam in nonlinear media with spatial nonlocality is investigated, and the transformation and propagation characteristics of astigmatic sinh-Gaussian beam in different transverse directions with different rotation angles are discussed. Some mathematical expressions of a rotating sinh-Gaussian beam are deduced, such as the propagation evolution, the beam width, the beam curvature, the critical power, etc. It is proved that the astigmatic sinh-Gaussian beam can keep the statistical width of the beam unchanged in any transverse direction during evolution, and the changes of beam width are diverse in two transverse directions. The influences of the rotation angle and the beam coefficients on the propagation characteristics are discussed and illustrated by numerical simulation.

Signal intensity of the random freeze beam in the biological turbulent tissue

Developing the signal intensity model for random freeze beams, which is an absorption- and diffraction-resistance beam, in the biological turbulent tissue, we investigate the signal intensity evolution of the random freeze beam as the function of the number of the superposition beam, beam waist, the topological charge of vortex modes, the fractal dimension, small length-scale factor, characteristic length of heterogeneity and the constant of refractive-index fluctuation of the tissue. The biological turbulent tissues include frozen human liver sections and the oxygenated (>99%) blood. The results are as follows: the signal transmittance of RF beam is greater than that of the BG beam. The impact of fractal dimension, the constant of refractive-index fluctuation, small length-scale factor and the natural length of heterogeneity on random freeze beam in the oxygenated (>99%) blood is similar to those in frozen human liver sections. The higher the number of superposition sub-beam, the larger the beam waist and the smaller the topological charge can efficiently improve the propagation performance of random freeze beams.

Waves in Flexural Beams with Nonlinear Adhesive Interaction

The paper studies the initial boundary value problem related to the dynamic evolution of an elastic beam interacting with a substrate through an elastic-breakable forcing term. This discontinuous interaction is aimed to model the phenomenon of attachment-detachment of the beam occurring in adhesion phenomena. We prove existence of solutions in energy space and exhibit various counterexamples to uniqueness. Furthermore we characterize some relevant features of the solutions, ruling the main effects of the nonlinearity due to the elastic-breakable term on the dynamical evolution, by proving the linearization property according to Gérard (J Funct Anal 141(1):60–98, 1996) and an asymptotic result pertaining the long time behavior.

Mathematical modelling of beam dynamics in diamagnetic confinement regime of open trap

The paper is devoted to the mathematical modelling of a beam injected into an open magnetic trap in the diamagnetic mode. The two-dimensional axially symmetric hybrid numerical model with the kinetic approximation for the ion component of the plasma and the MHD approximation for magnetized electrons is used. In the numerical experiments, the possibility of formation of the cavity in the magnetic field was shown. A detailed study of the evolution of the ion beam continuously injected into the trap is done, the dependencies on time, moment of injection and beam temperature are presented. The obtained results may be used for the data analysis of the laboratory experiments in open magnetic systems.

Investigation of a dual-hole structure-based broadband femtosecond nondiffracting SPP beam emitter by photoemission electron microscopy

Nondiffracting surface plasmon polariton (SPP) beam, which has unique self-healing and non-divergence properties, can be a good candidate in the next-generation on-chip devices and has attracted considerable attention. Here, a simple and broadband coupled femtosecond nondiffracting SPP beam emitter based on a dual-hole structure has been demonstrated and characterized by photoemission electron microscopy (PEEM). The PEEM experiments show that, compared with the usual one-color PEEM, the two-color PEEM scheme offers a clear image of the nondiffracting SPP by effectively reducing the influence of the light-SPP interference field. As a result, the parameters of the nondiffracting SPP beam, such as the divergence angle, waist width, and propagation distance, are experimentally determined. The PEEM images of the nondiffracting SPP are well reproduced by the finite-difference time-domain (FDTD) method. This work plays a vital role in the further study of, e.g., high spatial and temporal characterization of the dynamic evolution of nondiffracting SPP beam.

Improving surrogate model accuracy for the LCLS-II injector frontend using convolutional neural networks and transfer learning

Machine learning (ML) models of accelerator systems (‘surrogate models’) are able to provide fast, accurate predictions of accelerator physics phenomena. However, approaches to date typically do not include measured input diagnostics, such as the initial beam distributions, which are critical for accurately representing the beam evolution through the system. In addition, these inputs often vary over time, and models that can account for these changing conditions are needed. As beam time for measurements is often limited, simulations are in some cases needed to provide sufficient training data. These typically represent the designed machine before construction; however, the behavior of the installed components may be quite different due to changes over time or static differences that were not modeled. Therefore, surrogate models that can leverage both simulation and measured data successfully are needed. We introduce an approach based on convolutional neural networks that uses the drive laser distribution and scalar settings as inputs for a photoinjector system model (here, the linac coherent light source II, LCLS-II, injector frontend). The model is able to predict scalar beam parameters and the transverse beam distribution downstream, taking into account the impact of time-varying non-uniformities in the initial transverse laser distribution. We also introduce and evaluate a transfer learning procedure for adapting the surrogate model from the simulation domain to the measurement domain, to account for differences between the two. Applying this approach to our test case results in a model that can predict test sample outputs within a mean absolute percent error of 9%. This is a substantial improvement over the model trained only on simulations, which has an error of 261% when applied to measured data. While we focus on the LCLS-II Injector frontend, these approaches for improving ML-based online modeling of injector systems could be easily adapted to other accelerator facilities.

Longitudinal phase space improvement of a continuous-wave photoinjector toward X-ray free-electron laser application

The electron source still remains a major challenge for continuous-wave (CW) X-ray free-electron lasers (FELs). In this paper, we study the feasibility of an injection line based on a DC and superconducting radio-frequency (SRF) combined photocathode injector. We present a detailed investigation on the longitudinal phase space evolution of the electron beam along the injection line. We also analyze the main issues determining the high-order energy spread and current skewness. Based on the analysis, we propose to use a harmonic cavity as the buncher for the injection line. Simulation shows that an extracted electron beam with a normalized RMS emittance of 0.37 μm, an RMS bunch length of 1.0 mm, a high-order RMS energy spread of 2.75 keV, and a current skewness of 0 can be obtained at the bunch charge of 100 pC. This study is meaningful to the design of the injection lines for short-wavelength CW FELs, including those based on normal-conducting very-high-frequency (VHF) guns or DC guns.

Resistance to cracking of concrete containing waste rubber aggregates under cyclic loading using the acoustic emission technique

Abstract Recycling rubber aggregates from used grinded tires is a behavior of environmental protection. By performing cyclic flexural tests, this paper explores the effect of rubber aggregate content on the crack propagation of notched concrete beams containing waste rubber aggregates. The crack mouth opening displacement is tested. The acoustic emission technique is applied to detect the damage in the fracture process zone. The crack propagation is evaluated using the critical value of the mode I stress intensity factor. It was found that the crack length and stress intensity factor decrease with the increasing of rubber aggregates content. The crack length and stress intensity factor at failure under constant cyclic loading are larger than those at corresponding post-peak load level. It was observed that the damage evolution curves under cyclic envelope loading can be divided into three stages: initial-quick-stable stages. And they are S-shaped, quick-stable-accelerated curves under constant cyclic loading. Rubber aggregate reduces the acoustic emission activities in concrete specimens. Accumulations of acoustic emission hits, acoustic emission counts and acoustic emission energy are found in accordance with the damage evolution of concrete beam. The relation between damage and accumulative acoustic emission hits is quantified by fitting experimental data. The fitting curves agree well with test results.

Evolution of Heavy Ion Beam Probing from the Origins to Study of Symmetric Structures in Fusion Plasmas

The overview discusses development of the unique fusion plasma diagnostics—Heavy Ion Beam Probing (HIBP) in application to toroidal magnetic plasma devices. The basis of the HIBP measurements of the plasma electric potential and processing of experimental data are considered. Diagnostic systems for probing plasma in tokamaks TM-4, TJ-1, TUMAN-3M and T-10, stellarators WEGA, TJ-II and Uragan-2M are presented. Promising results of the HIBP projects for various existing modern machines, such as TCV, TCABR, MAST, COMPASS, GLOBUS-M2, T-15 MD and W7-X and the international fusion tokamak reactor ITER are given. Results from two machines with similar size and plasma parameters, but with different types of the magnetic con-figuration: axisymmetric tokamak T-10 and helically symmetric stellarator TJ-II are compared. The results of studies of stationary potential profiles and oscillations in the form of quasimonochromatic and broadband fluctuations, turbulent particle flux, fluctuations of density and poloidal magnetic field are presented. The properties of symmetric structures—zonal flows and geodesic acoustic modes of plasma oscillations as well as Alfvén Eigenmodes excited by fast particles from neutral beam injection heating are described. General trends in the behavior of electric potential and turbulence in magnetized fusion plasmas are revealed.

The upper Aptian–middle Albian Simplorbitolina lineage: an example of nepionic acceleration in Lower Cretaceous Orbitolinidae (Foraminifera)

ABSTRACT Evolutionary lineages within the conical agglutinated family Orbitolinidae are mainly evidenced by the increased complexity of their inner structure. In this respect, gradual changes in the exoskeleton resulting in the evolution of beams and rafters in the marginal zone refer above all to lineages within the subfamily Dictyoconinae. In contrast hereto, the increasing size and complexity of the simple megalospheric embryo as well as the reduction of the initial spiral stage defines lineages within the subfamily Orbitolininae (e.g., Praeorbitolina-Mesorbitolina). The case of the upper Aptian–middle Albian Simplorbitolina lineage, the ancestor-descendant relationship of the three species S. aquitanica, S. manasi, and S. conulus represents a rare example of the Dictyoconinae displaying a successive reduction of the initial spiral stage along with an increase of both embryo size and complexity of the marginal zone. This process, which is known as spiral reduction or nepionic acceleration, is well recorded from other groups of Larger Benthic Foraminifera (fossil and extant) such as the calcareous Rotaliida. The occurrences and palaeogeographic distributional pattern of Simplorbitolinas are reviewed. The present study is preliminary based on a well-preserved assemblage of megalospheric specimens of Simplorbitolina aquitanica (Schroeder) from the upper Aptian Reocín Formation of northern Spain (Cantabria).

Separate coupled solitons in biased series photorefractive semiconductor circuit

We present, for the first time a theoretical foundation for separately coupled solitons in a biased series circuit consisting of semi-insulating photorefractive multiple quantum well (MQW) waveguides. As an example, a slab semiconductor waveguide based on a GaAs/AlGaAs structure is considered. The coupled steady state space charge field is derived for both the MQW structures using a bipolar band transport model. Hence, a system of two coupled equations is obtained for each MQW structure which governs the dynamical evolution of light beams. We then prove the existence of dark–dark, grey–grey and grey–dark separately coupled soliton pairs. We also see that the soliton propagating individually in one PR semiconductor can affect the other by the light-induced current. We investigate this coupling effect with respect to the soliton beam’s intensity profile and for each of the three cases, namely, dark–dark, grey–grey and grey–dark separately coupled solitons. Some potential applications are discussed.