Electron vortices generation of photoelectron of H_(2)^(+) by counter-rotating circularly polarized attosecond pulses

Molecular-frame photoelectron momentum distributions(MF-PMDs) of an H_(2)^(+) molecule ion in the presence of a pair of counter-rotating circularly polarized attosecond extreme ultraviolet laser pulses is studied by numerically solving the two-dimensional time-dependent Schrodinger equation within the frozen-nuclei approximation. At small time delay, our simulations show that the electron vortex structure is sensitive to the time delay and relative phase between the counterrotating pulses when they are partially overlapped. By adjusting time delay and relative phase, we have the ability to manipulate the MF-PMDs and the appearance of spiral arms. We further show that the internuclear distance can affect the spiral vortices due to its different transition cross sections in the parallel and perpendicular geometries. The lowest-order perturbation theory is employed to interpret these phenomena qualitatively. It is concluded that the internuclear distancedependent transition cross sections and the confinement effect in diatomic molecules are responsible for the variation of vortex structures in the MF-PMDs.

用数值模式匹配算法高效仿真轴对称型散射体海洋可控源电磁响应

圆盘、球体以及球冠状体是地球物理研究中非常重要的一类散射类型.在海洋环境中,圆盘可以用于描述玄武岩基岩以及油气圈闭构造等电阻率异常体,而球冠可以近似描述某些基岩隆起或起伏地形等.这类散射体的一个重要特征是其电阻率空间分布具有轴对称性.如果能够针对这类形状的散射体研究建立一套有效的海洋可控源电磁数值模拟方法,对于认识复杂地层条件下海洋电磁响应的变化特征、研究建立相关的资料处理和解释方法具有非常重要的意义.本文根据电导率轴对称分布特征,设法用一个或多个不同半径、不同厚度的水平同心圆盘逼近这类轴对称电导率散射体,并将这些同心圆盘与海洋环境中的空气、海水、沉积层和基岩等背景介质结合,形成一个在水平方向电导率具有轴对称分布、在垂直方向又具有分层特征的水平层状非均质模型.在此基础上,应用数值模式匹配法研究水平电偶极子天线电磁场的数值模拟方法,给出位于对称轴上的水平发射天线电磁场在层状非均质地层中的半解析解,建立海洋可控源电磁响应高效算法.最后通过数值模拟结果对该算法进行检验并考察海洋可控源三维电磁响应特征.

正电子冲击下氦电离三重微分截面的理论计算

我们发展了一种处理正电子碰撞原子电离的畸变波Born近似方法,在这个方法中,正负电子偶素通道通过一个ab initio的光学势附加到入射粒子和靶的相互作用势上,且该通道对电离的影响被第一次被考虑在正电子碰撞原子电离的过程中.我们运用这个方法计算了在50 eV入射能量范围氦的电离的三重微分截面,计算结果和实验数据很好的符合.

初中物理实验教学方法的创新思路

现如今,人们对初中物理教学越来越重视,而在物理教学中,实验是必不可少的重要部分,在物理实验教学中,教师为学生演示实验,学生根据自己掌握的知识实践实验,有助于初中生综合学习能力、实践能力与解决问题能力的提高,促进他们物理学科素养的形成。基于此,物理教师须创新教学方法,对实验教学予以高度重视。

Low Energy Scattering of Electrons by Sodium

The low energy scattering of electrons by sodium at incident energies up to ionization threshold are calculated by applying the momentum space coupled-channel-optical （CCO） method. The present results are in good agreement with the previous experimental and theoretical results. Furthermore, three resonances in the total cross sections observed by previous experiments are proved by the present calculation.

Chirp-dependent ionization of hydrogen atoms in the presence of super-intense laser pulses

We perform a theoretical study on dynamic interference in single photon ionization of ground state hydrogen atoms in the presence of a super-intense ultra-fast chirped laser pulse of different chirp types(equal-power and equal-FWHM laser pulses)by numerically solving the time-dependent Schrödinger equation in one dimension.We investigate the influences of peak intensity and chirp parameters on the instantaneous ionization rate and photoelectron yield,respectively.We also compare the photoelectron energy spectra for the ionization by the laser pulses with different chirp types.We find that the difference between the instantaneous ionization rates for the ionization of hydrogen atom driven by two different chirped laser pulses is originated from the difference in variation of vector potentials with time.

Relativistic electron scattering from freely movable proton/μ^+ in the presence of strong laser field

We have investigated the electron scattering from the freely movable spin-1/2 particle in the presence of a linearly polarized laser field in the first Born approximation.The laser-dressed state of electrons is described by a time-dependent wave function which is derived from a perturbation treatment.With the aids of numerical simulations, we explore the dependencies of the differential cross section on the laser field intensity as well as the electron-impact energy.Due to the mobility of the target, the differential cross section of this process is smaller than that of Mott scattering.

Study of(e,2e) process on potassium at 6 e V-60 eV above threshold in a second-order Born approximation

The standard distorted wave Born approximation （DWBA） method has been extended to second-order Born amplitude in order to describe the multiple interactions between the projectile and the atomic target. Second-order DWBA calculations have been preformed to investigate the triple differential cross sections （TDCS） of coplanar doubly symmetric （e, 2e） collisions for the alkali target potassium at excess energies of 6 eV-60 eV. Compared with the previous first-order DWBA calculations, the present theoretical model improves the degree of agreement with experiments, especially for the backward scattering angle region of TDCS. This indicates that the present second-order Born term is capable of giving a reasonable correction to the DWBA model in studying coplanar symmetric （e, 2e） problems in low and intermediate energy ranges.

Positronium formation for positron scattering from metastable hydrogen

Positronium （Ps） formation for positron impact on metastable hydrogen in 2s state has been studied by using the two- channel, two-center eikonal final state-continuum initial distorted wave （EFS-CDW） method. The differential, integrated, and total cross sections for Ps formation in different states have been calculated from each channel opening thresholds to high energy region. The results are compared with other theoretical calculations available in the literature. For Ps formation in s-state at intermediate and high energies, our results are in good agreement with the prediction of distorted wave theory. Those formed in p-states and the total Ps formation cross sections are reported for the first time. It is shown that the total Ps formation cross sections for positron scattering from H（2s） state are significantly larger at relatively low energies, while smaller at high energies, compared with those obtained from hydrogen in ground state.

Resonances in Electron Impact on Atomic Oxygen

The momentum-space coupled-channels-optical （CCO） method is used to study the resonances in electron oxygen collision in the energy region of 9-12 eV, Present results have shown agreement with the available experimental and theoretical results, and new positions of resonances are found by the comparison of total cross sections,

Electron Impact Ionization Cross Section of Nitrogen Atoms

The direct ionization cross sections for electron scattering by nitrogen are calculated by applying an equivalentlocal optical model from 15eV to 1100eV. The present results are compared with the experimental data and other theoretical calculation results.

Coupled-channels optical calculation of positron hydrogen resonances

An application of the coupled-channels optical method is given for the energy-dependent phenomena of positron- hydrogen resonances below the n = 2 excitation threshold. The equivalent local optical potential is used to account for the target polarization and positronium formation. The calculation includes 9 explicitly physical coupled channels. The lowest S-wave resonance energy position and new resonances are found. Angular dependence of the cross section in the resonance region are investigated.

Resonances in Positron Hydrogen Scattering above the H (n=2) Threshold

We investigate high partial wave resonances in positron-hydrogen scattering using the momentum-space coupledchannels optical method above the H (n =2) threshold.Resonances with angular momenta of L =0-6 are reported.Ionization continuum and positronium formation channels are included via a complex equivalent local potential.Comparisons with the existing theoretical results are presented.

Differential cross sections of positron-hydrogen collisions

We make a detailed study on the angular differential cross sections of positron–hydrogen collisions by using the momentum-space coupled-channels optical（CCO） method for incident energies below the H ionization threshold. The target continuum and the positronium（Ps） formation channels are included in the coupled-channels calculations via a complex equivalent-local optical potential. The critical points, which show minima in the differential cross sections, as a function of the scattering angle and the incident energy are investigated. The resonances in the angular differential cross sections are reported for the first time in this energy range. The effects of the target continuum and the Ps formation channels on the different cross sections are discussed.