Lightfront DHW Functions and Strong Field QED

We investigate strong-field effects in QED using a phase space approach based on the Dirac–Heisenberg–Wiger function. We calculate the electron–positron DHW function in a null (laser) field background exactly, using lightfront field theory. The DHW function exhibits the distinct features of strong-field QED: in particular we explicitly identify the effective fermion mass for arbitrary temporal pulse profiles.     

Quantum and Classical Radiation Reaction from Lightfront QED

We examine dynamical radiation reaction in lightfront QED. We take the classical limit and compare with predictions from various classical equations of motion.     

Single-atom-response to a Partially Coherent Intense Laser Field

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Pondermotive Shift of Photoelectron Spectra in Intense Laser Field

In a recent experimental work on the excess photon detachment （EPD） of H^- ions [Phys. Rev. Lett. 87 （2001） 243001] it has been found that the ponderomotive shift of each EPD peak increases with the order of the EPD channel. By using a nonperturbative quantum scattering theory, we obtain the kinetic energy spectra for the differential detachment rate Mong the laser polarization for several laser intensities. It is demonstrated that higher order EPD peaks are produced mainly at relatively higher laser intensities. By calculating the overall EPD spectra with varying laser intensities, it is found that the ponderomotive shift of each EPD peak increases with the order of the EPD channel Our calculations are in good agreement with the experimental observation. It is found that different EPD channels occur mainly when the laser field reaches some values, thus the intensity distribution of the laser field is responsible for the varying ponderomotive shifts.     

强光场中原子的电离速率

以静态场隧道电离为基础,在准静态近似的条件下,对描述强光场中原子及其各阶离子电离的电离速率进行了较为系统的总结,纠正了早期对隧道电离的电离速率公式进行讨论并且后来的计算中被广泛引用的文献「１０」中公式的错误,地部分稀有气体原子及其各了子在线偏振、圆偏振强光场中的了速度及相应的阈值光强进行了比较。     

强激光场中H2^＋离解行为的研究

在多电子态模型下，利用二阶劈裂传播子算法计算了Ｈ２＾＋在强激光场中的离散行为。结果发现在高频场时分子的多光子离散碎片是近对称的，而对于低频场，在所考虑的激光强度下Ｈ２＾＋是被隧道离散的，因而其离散碎片Ｈ＾＋分布是反对称的，另外，文中还探讨了三脉冲形状对分子离解几率、离解碎片动力学行为的影响。     

Hydrodynamics of Plasma Interaction with an Intense Laser Field

A set of moment relations, which can describe the charged fluids response to an intense pump laser, and a linearization substitution relation, which is more appropriate as compared with the past treatment, are given by theoretical analyses. The relevant equations of state (adiabatic and isothermal), momentum and energy equations are derived self-consistently.The dispersion relations of the electron plasma wave and the ion acoustic wave driven by an intense pump laser field are-obtained. The results show that the frequencies of both the excited electron plasma wave and the excited ion acoustic wave have a great modification in the case of strong pump. The former bears out the theoretical result obtained from Vlasov equation and the later is consistent with experimental observations. It is proved that the zero-frequency component of the laser light wave contribution to the plasma pressure tensor is un-neglected,which implies a greatly change to the wave excitation properties, particularly in the direction of parallel or approximately parallel to the laser field vector.     

Photoelectron Angular Distributions of Positronium in Intense Laser Field

When positronium is generated in super intense laser fields irradiated by an intense laser field, it breaks up into an electron and a positron. The momentum of the electron as well as that of the positron depends on the relative direction with respect to the laser propagation. Thus, the photoelectron angular distributions show inversion asymmetry. The inversion asymmetry becomes notable for higher kinetic energy of electrons.     

External Field QED on Cauchy Surfaces for Varying Electromagnetic Fields

The Shale–Stinespring Theorem (J Math Mech 14:315–322, 1965) together with Ruijsenaar’s criterion (J Math Phys 18(4):720–737, 1977) provide a necessary and sufficient condition for the implementability of the evolution of external field quantum electrodynamics between constant-time hyperplanes on standard Fock space. The assertion states that an implementation is possible if and only if the spatial components of the external electromagnetic four-vector potential \({A_\mu}\) are zero. We generalize this result to smooth, space-like Cauchy surfaces and, for general \({A_\mu}\), show how the second-quantized Dirac evolution can always be implemented as a map between varying Fock spaces. Furthermore, we give equivalence classes of polarizations, including an explicit representative, that give rise to those admissible Fock spaces. We prove that the polarization classes only depend on the tangential components of \({A_\mu}\) w.r.t. the particular Cauchy surface, and show that they behave naturally under Lorentz and gauge transformations.     

强激光场中一维原子的渐近边界条件

用Fourier变换推导了强激光场中一维原子模型的渐近边界条件,分析了三类渐近边界条件的误差,用第一类渐近边界条件和非齐线性正则方程的辛算法计算了强激光场中一维氢原子的几率分布和平均能量,并将结果与理论分析进行了比较.     

Controlling Three-Dimensional Electron-Electron Correlation via Elliptically Polarized Intense Laser Field

The three-dimensional electron-electron correlation in an elliptically polarized laser field is investigated based on a semiclassical model. Asymmetry parameter α of the correlated electron momentum distribution is used to quantitatively describe the electron-electron correlation. The dependence of α on ellipticity ε is totally different in three directions. For the z direction(major polarization direction), α first increases and reaches a maximum at ε = 0.275, then it decreases quickly. For the y direction in which the laser field is always absent, the ellipticity has a minor effect, and the asymmetry parameter fluctuates around α =-0.15. However, for the x direction(minor polarization direction), α increases monotonously with ellipticity though starts from the same value as in the y direction when ε = 0. The behavior of α in the x direction actually indicates a transformation from the Coulomb interaction dominated correlation to the laser field dominated correlation. Therefore, our work provides an efficient way to control the three-dimensional electron-electron correlation via an elliptically polarized intense laser field.     

强场物理中自生磁场的实验研究

为了获得飞秒激光与固体靶相互作用中自生磁场的大小与空间分布情况, 利用光学多道分析（OMA）谱仪（谱分辨0.1nm ）加电荷耦合器件（CCD）相机（11521242）探测设备, 用消色差的相机镜头作为空间分辨,在固体靶前表面测量了激光的高次谐波（n0）光谱, 观测到了n0光谱的精细结构及其频率间隔,由此推出激光与固体靶相互作用中产生的等离子体内的自生磁场达60-70特斯拉（T）量级, 且越接近靶法线方向磁场越强,其一维空间分布为环形。 这一结果为进一步研究强场物理中自生磁场的特性及等离子体的整体行为提供了依据。     

On the Light-Cone Expansion in Gauge Field Theories (QED)

The techniques for the derivation of light-cone expansions in scalar field theories are generalized to nonscalar, especially gauge field theories. For this reason the smallness of the remainder is proved in an arbitrary renormalizable theory provided an infrared regularization is present. Then we apply the formalism to derive a light-cone expansion for the product of two scalar currents in Quantum Electrodynamics in leading order. Thereby the gauge-invariance of the underlying theory is used from the very beginning by the application of the known solutions of the Ward identities. As a result of that, one obtains two gauge-invariant light cone operators, and the corresponding coefficient functions are independent one from another.     

强场物理—一门崭新的学科

强场物理是一门正在形成之中的新学科，给许多传统学科带来了巨大的冲击和发展机遇。文章简要评述了强场物理目前的研究热点。     

超短脉冲强激光场中电子剩余能计算

为了控制光场感应电离等离子体的温度以使得基于光场感应电离机制的X射线激光辐射获得更高的增益值,利用准静态隧道电离模型,定量计算了电子剩余能量与激光偏振参量、波长(频率)、激光强度以及电离介质电离能的变化关系。计算结果表明线偏振短波长激光以及高电离能介质产牛的等离子体中电子剩余能比较低,因此适合用作复合机制X射线激光;对于低价离子存偏振度α介于0～1之间的某一处最高,因此,可以通过调整偏振度α,获得某一椭圆偏振光,会更有利于基于光场感应电离电子碰撞机制X射线激光增益的提高。     

电子在强聚焦激光场中的动力学轨道

模拟研究了具有一定初态能带的相对论电子在强聚焦激光场中的动力学特性，发现激光场强达a0=eE／m，cw≥5，有三种典型的动力学轨道：电子俘获加速轨道CAS（Capture＆Acceleration Scenario），非弹性散射轨道IS（Inelastic Scattering），电子穿进轨道PARM（Penetrate into Axial Region and Move）。发现穿进轨道PARM的出现强烈依赖于腰宽w0，住膛宽较小（激光腰宽w0≤30）时较明显，其出现与紧聚焦激光场衍射效应较强有火。在腰宽较小时，随着脉冲长度的减小，PARM的出现概率减小，而IS的出现概率增大。本文探讨了三种轨道物理机制的区别。为聚焦激光场加速电子提供参考。     

双色激光场中一维氢分子的经典动力学性质研究

应用经典理论方法,采用辛算法,数值求解双色激光场作用下的一维共线氢分子的哈密顿正则方程,得到氢分子在激光场作用下的经典轨迹,并计算H₂⁺,H₂²⁺,H,H⁺等产物的产生概率随时间的演化,分析了双色场的光强、倍频、相位的变化对氢分子动力学性质的影响并给出相关的物理解释.     

Nonclassical Field States in Quantum Optics and Particle Physics

The primary aim of the present paper is to draw the attention of particle physicists to new developments in studying squeezed and correlated states of the electromagnetic field, and those working on the latest developments to new findings about multiplicity distributions and other specific effects in quantum chromodynamics. New types of nonclassical states used in quantum optics such as squeezed states, correlated states, and even and odd coherent states (Schrödinger cat states) for one-mode and multimode interactions are reviewed. Their distribution functions are analyzed according to the method first used for multiplicity distributions in high-energy particle interactions. The phenomenon of oscillations of particle distribution functions of squeezed fields is described and related to the phenomenon of oscillations of cumulant moments of some distributions for squeezed and correlated field states. Possible extension of the method to fields different from the electromagnetic field (gluons, pions, etc.) is conjectured, and some predictions of specific effects in nucleus-nucleus interactions at high energies are presented.     

The Photoionization of Atomic Hydrogen in an Intense Circularly Polarized Laser Field

We calculate nonperturbatively the irfluence of a strong circularly polarized laser beam on the hydrogen atom energy levels by making use of the time-independent formalism proposed by one of us. The photoionization cross section of the hydrogen atom irradiated by this laser beam and the angular distribution of photoelectrons are also calculated. From the numerical results we clearly see the intensity dependence of the whole photoionization process,including the intensity dependence of the photoelectron energies.