Electron-Helium Scattering in Free-Free Transitions in a Bichromatic Laser Field

Theoretical calculation of the differential cross section （DCS） for elastic electron-helium scattering in the presence of a bichromatic CO2 laser field is carried out in the first Born approximation with a simple screening electric potential. The two components of the laser field have the frequencies w and 2w, which are out of phase by an arbitrary scale φ. The variations of the differential cross section as a function of the phase angle φ in the domain 0°≤ φ ≤360° are presented. We discuss the influence of the number of photons exchanged on the phase-dependee effect. Moreover, for different scattering angles and incident electron energies, the DCS has outstanding ditferences. These illustrate that the two parameters have important effects on the differential cross section and the screening electric potential is effective.     

erent Phase Control in e-Ar Scattering in a Bichromatic Laser Field in the Second Born Approximation

We study the elastic scattering of atomic argon by an electron in the presence of a bichromatic laser field in the second Born approximation. The target atom is approximated by a simple screening potential. We explore the dependences of the differential cross sections on the relative phase φ between the two components of the radiation field and discuss the influence of the number of photons exchanged on the phase-dependence effect. Moreover, for different scattering angles and incident electron energies, the differential cross sections are notably different.     

Effect of the Initial Laser Phase on the Interaction Between Relativistic Electron and Ultra－Intense Laser Field in a Strong Uniform Magnetic Field

We investigate the influence of the initial laser phase on the interaction between relativistic electron and ultraintense linear polarized laser field in a strong uniform magnetic field. It is found that the dynamic behaviour of the relativistic electron and the emission spectrum varies dramatically with different initial laser field phases.The effect of changing initial phase is contrary in the two parameter regions divided by the resonance condition.The phase dependence of the electron energy and velocity components are also studied. Some beat structure is found when the initial laser phase is zero and this structure is absent when the initial laser phase is a quarter of a period.     

Influence of a high-speed dielectric spherical particle''''s movement on its scattering characteristics

The scattered field and differential scattered section (DSS) of a moving spherical particle with a high speed are investigated numerically.The coordinate and vector transformations are used to establish a theoretical basis for studying the laser scattering of a moving particle.The DSS of a moving spherical particle is explained by the electric and magnetic field from Mie scattering theory.Assuming the laser wavelength of 1.06μm,we compute the ratio of the laser DSS of the moving dielectric spherical particle to that of the static dielectric spherical particle,which changes with radii,speeds and scattering angles of the particle.The numerical results show that the laser DSS of the moving spherical particle is tightly connected with its speed and scattering zenith angle.If a spherical particle moves with high speed,the laser DSS due to movement of the particle could not be neglected.If the speed of the dielectric spherical particle is fluctuating,the Doppler effect and the frequency spectrum expansion play important roles.     

Theoretical Analysis of the Critical Phenomena of a Brillouin Laser

The critical phenomena of a Brillouin laser are analyzed theoretically. The results show that the behavior of a Brillouin laser in the threshold region is a second-order phase transition. The critical point of the phase transition is the gain threshold of the Brillouin laser, and the order parameter is the amplitude of the Stokes component in stimulated Brillouin scattering. The critical slow-down phenomenon and the typical characteristics in phase transition are demonstrated. Further work on the combination of nonlinear optics and phase transition in the Brillouin laser may lead to a new view and findings that could be significant for both fields.     

Laser Tracking and Pointing at a Target with Stimulated Brillouin Scattering

Laser tracking and pointing at a simulated moving target in atmosphere 1.27 km away is realized experimentally,in which stimulated Brillouin scattering (SBS) phase conjugation technology and velocity compensation mirror are used. Only if the angle between the SBS phase conjugation laser and the illumination laser is smaller than the atmosphere isoplanatic angle ψo, is the wave-front aberration of laser beam produced by atmospheric turbulence compensated for in real time. This experiment was carried out with horizontal ranges 1.27km at 50m height above the ground, and Nd: YA G lasers are used. By changing the angle of a velocity compensation mirror reflecting the SBS phase conjugation laser to the simulated target, simulated targets with different moving velocities are tracked and pointed by the laser beam. The spot and energy distribution of illumination laser spot and SBS phase conjugation laser are recorded. The energy back to target is up to 75 mJ. The SBS phase conjugation laser spot shows that it is focused at the simulated moving target within a small area.     

Laser-Duration Dependence of Emission Properties of High-Order Harmonic Generation

Quantitative investigations are made for the laser-duration dependence of the emission properties of high-order harmonic generation （HHG）. HHG emission properties produced by few-cycle lasers show some useful characteristics. The cutoff energy is less than that by laser for infinite duration. The single energy distribution pulse decreases much faster than its duration as the laser duration grows. A two-cycle laser with carrier-envelope phase of 0° can produce a single distribution pulse peaked at the laser carrier phase 1.22 rad and spanned 1.18 rad with the cutoff energy 2.9Up ＋ Ip and a bandwidth 0.63Up, where Up is the ponderomotive potential of the laser field and Ip is the atomic ionization potential.     

Elastic wave scattering from rough free surfaces of solids

Elastic wave scattering by a rough free surface of solids is analyzed. The analysis is based on the concept of scattering amplitude (SA) and perturbation approximation. The SA method is very convenient for rough surface scattering problems. By solving the boundary equations, the first and the second order solutions of approximate scattering amplitude are obtained. The general solutions are used for, as an example, the wave scattering by rough surfaces with Gaussian distribution. The mean field and variance are given. Finally, an experiment is designed to verifv the theoretical predications.     

Positron-impact ionisation of atomic hydrogen in the presence of a bichromatic laser field

The positron impact-ionisation of atomic hydrogen in the presence of a linearly polarised bichromatic field is investigated in the first Born approximation.The field is composed of a fundamental frequency and its second harmonic.The state of positron in the field is described by the Volkov wavefunction,and the continuum state of the ejected electron is described by the Coulomb-Volkov wavefunction.The dressed ground state of target is a first order time-dependent perturbative wavefunction.The triple differential cross sections and their dependencies on laser field parameters are discussed and compared with the results modified by a monochromatic field.Numerical results show that the coherent phase control is significant and the laser-assisted ionisation cross sections caused by positron and electron are different.     

Acoustic scattering from a fluid-filled finite cylindrical shell in water:Ⅰ.Theory

Acoustic scattering from a submerged fluid-filled finite cylindrical shell insonified by an incident plane wave was studied.The analytic solutions of the scattering field are derived using the elastic thin shell theory with the boundary conditions.The fluid-filled impedance,due to the effect of internal fluid,must add to the impedance of the system.The results show that in the backscattering field,rigid scattering has a large contribution only on the broadside and elastic scattering play a major role when oblique incidence.The dispersion curves of the phase velocity show that comparing with the internal vacuum condition,except the contribution by longitudinal wave and shear wave near the broadside a series of the additional waves caused by the internal fluid is added which have great contribution to the scattering field.Bowl-shape resonance curves are presented in the frequency-angle spectrum as the contribution of the internal fluid waves.     

线偏振双色激光场中氪原子的阈上电离现象

采用基于Guo,Aberg和Crasemann发展的强激光场中的非微扰量子散射理论(GAC理论),研究了线偏振双色激光场中氪(Kr)原子阈上电离的光电子角分布,双色激光场由一系列相同的单周期激光脉冲组成.研究发现光电子角分布有强烈的位相依赖关系,且呈现出反演不对称性、喷射结构和展宽结构等现象,这为实验上通过改变双色激光场的相对相位来观察和控制光电子角分布提供了一种有效的方法.     

Phase signatures in laser-assisted electron-atom collisions

We study electron-atom scattering in the presence of a laser field with elliptic polarization. We discuss the dependence of the differential cross sections for the cases of circular and linear polarizations as a function of scattering angle. Interesting typical signatures of the phase between the two components of the circular polarization of the laser field appear in the differential cross section.     

Compton散射下等离子体中电子相轨道的演化

用KMR模型研究了等离子体中多光子非线性Compton散射下电子相轨道的演化,发现电子与光子进行能量交换后,只有未被俘获电子的相轨道才能从周期性向非周期性、随机型演化,其演化剧烈程度随电子吸收光子数的增大而加剧,随电子与光子碰撞非弹性成分和碰撞前初始速度的增大而迅速减弱,但低于强激光场中的剧烈程度。当电子被光场俘获时,这种演化过程结束并做稳定的运动,光子不再为电子提供能量。     

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用KMR模型研究了等离子体中多光子非线性Compton散射下电子相轨道的演化,发现电子与光子进行能量交换后,只有未被俘获电子的相轨道才能从周期性向非周期性、随机型演化,其演化剧烈程度随电子吸收光子数的增大而加剧,随电子与光子碰撞非弹性成分和碰撞前初始速度的增大而迅速减弱,但低于强激光场中的剧烈程度。当电子被光场俘获时,这种演化过程结束并做稳定的运动,光子不再为电子提供能量。     

A New Scheme for High‐Intensity Laser‐Driven Electron Acceleration in a Plasma

We propose a new approach to high‐intensity relativistic laser‐driven electron acceleration in a plasma. Here, we demonstrate that a plasma wave generated by a stimulated forward‐scattering of an incident laser pulse can be in the longest acceleration phase with injected relativistic beam electrons. This is why the plasma wave has the maximum amplification coefficient which is determined by the acceleration time and the breakdown (overturn) electric field in which the acceleration of the injected beam electrons occurs. We must note that for the longest acceleration phase the relativity of the injected beam electrons plays a crucial role in our scheme. We estimate qualitatively the acceleration parameters of relativistic electrons in the field of a plasma wave generated at the stimulated forward‐scattering of a high‐intensity laser pulse in a plasma. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thomson scattering from ultrashort and ultraintense laser pulses

The Thomson scattering in an ultraintense ( approximately 10(18) W cm(-2)) and ultrashort (20 fs) laser field is calculated that demonstrates different characteristics from those of the low-intensity field case. The electron trajectory no longer conforms to a figure-eight pattern, and the spectra demonstrate complex shifting and broadening to suggest that Thomson scattering can be used for characterizing pulsed lasers. The initial phase at the electron entrance of the field can critically affect the Thomson scattering, but its effect is weighted by the intensity profile of the field. As a result, the fourfold symmetry of the radiation pattern breaks down when the electron enters the field closer to the pulse peak. The relationship between the Thomson scattering and Compton scattering in the high field is analyzed.     

The second Born approximation of electron–argon elastic scattering in a bichromatic laser field

We study the elastic scattering of atomic argon by electron in the presence of a bichromatic laser field in the second Born approximation. The target atom is approximated by a simple screening potential and the continuum states of the impinging and emitting electrons are described as Volkov states. We evaluate the S-matrix elements numerically. The dependence of differential cross-section on the relative phase between the two laser components is presented. The results obtained in the first and second Born approximations are compared and analysed.     

偏振相移与相位共轭结合的散射光聚焦技术研究

散射介质对光的随机散射作用是制约其光学聚焦和成像的重要因素，光学相位共轭技术能够通过对散射光场共轭还原实现透过散射介质的光学聚焦和成像，其中散射光场相位的获取是共轭还原的核心。阐述了偏振相移的基本原理，将偏振相移与相位共轭技术相结合，设计了新的基于偏振相移的数字光学相位共轭系统。采用633 nm的HeNe激光器作为系统光源，毛玻璃作为散射介质开展散射光聚焦实验研究。实验结果表明:该装置能够成功实现透过散射介质的光学聚焦，其中聚焦点与背景光强的比值可达约400倍。     

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应用电子和多光子集团非弹性碰撞模型和冷等离子体模型，研究了飞秒强激光与线性等离子体发生多光子非线性Compton散射时，散射激光与入射激光形成的飞秒耦合激光场对线性等离子体层中光场和电子密度分布的影响。研究发现，在耦合激光的有质动力作用下，电子密度分布和离子密度分布比Compton散射前的偏离更加严重，电子密度的变化比离子密度的变化更快，产生的静电场更强。即使耦合激光场非常弱，电子的运动仍表现出相对论效应，仍有静电场存在。     

Interference effects in the theory of multiphoton laser-simulated bremsstrahlung for electron wave packets that are broad in their momentum representation

The interference peculiarities of absorption and emission of external laser field quanta by a spatially narrow electron wave packet during its scattering at a potential center are considered. The angular and energy distributions for an electron due to scattering in a laser field are obtained and analyzed within the framework of the perturbation theory based on interaction with the potential center. A new mechanism of effective heating of plasma produced in a cluster under the effect of intense external laser field is found. Drastic changes in angular distribution due to the interference of incident and scattered parts of an electron wave packet are revealed.