Relativistic three-body recombination with the QED vacuum

Electron-positron pair annihilation into a single photon is studied when a second free electron is present. Focussing on the relativistic regime, we show that the photon emitted in the three-lepton interaction may exhibit distinct angular distributions and polarization properties. Moreover, the process can dominate over two-photon annihilation in relativistic electron-positron plasmas of few-MeV temperature. An analogy with three-body recombination of electrons with ions is drawn.     

相对论飞秒激光脉冲在真空中对预加速电子的加速

通过求解电子运动的相对论方程，发现预加速电子在超强超短激光脉冲的作用下可以获得很高的能量增益. 飞秒激光脉冲的上升沿在焦点附近的区域有效加速电子后，电子和光脉冲一起传播一段距离（远大于瑞利长度）后，激光强度变得很弱，从而使脉冲下降沿对电子的减速作用可以忽略不计，因此电子只经历加速过程而没有被减速，当电子和光脉冲分离时，电子获得了很高的能量增益. 当光强为10¹⁹Ｗ／cm² ，电子的初始能量为MeV量级时，电子的能量增益可以达到01GeV. 进一步讨论了电子的能量增益与电子的初始条件与激光脉冲的参数之间的关系. 关键词： 电子加速 飞秒激光脉冲 能量增益     

紧聚焦的超短超强激光脉冲在真空中加速斜入射的相对论电子

研究了紧聚焦的线偏振飞秒超强高斯激光脉冲俘获并剧烈加速斜入射低能相对论电子的效应 ，发现被俘获的电子在激光脉冲纵向有质动力的强大加速作用下，可以获得GeV量级的能量 ，并详细研究了入射电子的初能量、斜入射角、电子与激光脉冲的相对延迟时间和激光脉冲 宽度等条件对电子能量增益的影响，发现当激光脉宽超过10λ时，脉宽对电子能量增益影响 不大. 关键词： 电子加速 有质动力 能量增益 束腰     

High-energy,nuclear, and QED processes in strong laser fields

Various applications of ultraintense laser fields in particle physics, nuclear science, and quantum electrodynamics are presented. We discuss laser-driven lepton-pair creation, photon splitting, high-harmonic generation from both vacuum and muonic atoms, and direct nuclear excitation. All of these processes may come into experimental reach by near-future laser technology.     

Nonlinear interaction of strong laser fields in vacuum

Quantum electrodynamics (QED) predicts that electromagnetic fields interact with each other in vacuum. We study the possibility of revealing this interaction experimentally with intensities on the order of 10²⁴–10²⁶ W/cm², which may be available in the next generation of laser systems. In particular, we investigate high-order harmonic generation in vacuum via the collision of two ultrastrong counterpropagating laser pulses. The experimental feasibility of the related process of stimulated light-by-light scattering is also examined. Finally, the importance of including diffractive effects to describe the nonlinear interaction between an x-ray probe and a strong, focused optical standing wave is pointed out.     

The vacuum energy of QED with four-fermion interaction

We consider quantum electrodynamics in the quenched approximation including a four-fermion interaction with coupling constantg. The effective potential at stationary points is computed as a function of the coupling constants α andg and an ultraviolet cutoff Λ, showing a minimum of energy in the (α,g) plane for α=α _c =π/3 andg=∞. When we go to the continuum limit (Λ→∞), keeping finite the dynamical mass, the minimum of energy moves to (α=0,g=1), which correspond to a point where the theory is trivial.     

强激光与柱腔靶作用下准直高能电子束的产生

利用二维PIC粒子模拟程序研究了超短超强激光脉冲与柱腔靶相互作用产生的表面超热电子加速现象。采用光强为1021 W/cm2量级的超高斯激光脉冲掠入射进入柱腔靶,在靶的内壁上观察到了GeV量级的表面超热电子。超热电子束被准静态的电场和磁场约束在内壁表面附近,保证了电子束的准直性,发散角仅为1.6°;并且由于超热电子束在纵向激光电场中加速了mm级的距离,激光到高能电子(100 MeV)的转换效率达到了26.6%。另外,通过多参数模拟和理论解析讨论了激光的光强以及横向空间分布对这种表面超热电子加速的影响。     

QCD corrections to QED vacuum polarization

We compute QCD corrections to QED calculations for vacuum polarization in background magnetic fields. Formally, the diagram for virtual eē loops is identical to the one for virtual qq̄ loops. However, due to confinement, or to the growth of α_s as p² decreases, a direct calculation of the diagram is not allowed. At large p² we consider the virtual qq̄ diagram, in the intermediate region we discuss the role of the contribution of quark condensates 〈qq̄〉 and at the low-energy limit we consider the π⁰, as well as charged pion π⁺π^- loops. Although these effects seem to be out of the measurement accuracy of photon–photon laboratory experiments, they may be relevant for γ-ray burst propagation. In particular, for emissions from the center of the galaxy (8.5 kpc), we show that mixing between the neutral pseudo-scalar pion π₀ and photons renders a deviation from the power-law spectrum in the TeV range. For scalar quark condensates 〈qq̄〉 and virtual qq̄ loops are relevant only for very high radiation density ∼300 MeV/fm³ and very strong magnetic fields of order ∼10¹4 T. PACS 12.20.Ds; 14.40.-n; 12.38.Aw; 14.65.Bt     

Particle acceleration in ultra-intense laser plasma interaction

The acceleration of electrons in laser plasma interaction has been observed since the seventies, when it was initially considered as a deleterious effect, as, in the inertial fusion context, the so-called suprathermal electrons preheat the target. However, it has been quickly observed that a large benefit could be taken from these electrons. Two main directions are now followed. In the first direction, one tries to accelerate electrons to high energy, presently in the GeV range. The electrons may originate from a pre-accelerated beam, or directly from a gas target instantaneously transformed in a plasma by the ultra-intense laser pulse. In the second direction, one tries to transfer the energy of the electrons to fast ions, especially protons, presently in the few tens of MeV range. Thin targets are used for this transformation, the electrons being accelerated at the front of the target, while the ions may originate from the front part or the back part of the target, or from inside the target, depending on the parameters of the experiment. While the maximum energy was the initial goal of the pioneer experiments, there are now strong experimental efforts to improve the quality of the beams, in terms of luminosity, emittance, and energy spectrum. In the recent years, quasi-monoenergetic beams were obtained both for electrons and for ions.     

强场下真空中粒子对产生的研究进展

随着激光技术的飞快发展,激光强度不断提高,超强外场下真空中正负电子对产生的过程,即能量向质量转化过程,已经成为一个研究热点。主要综述了近几年量子Vlasov方程方法和计算量子场论(数值求解Dirac方程)方法在研究强场下真空中正负电子对产生方面的进展,分别介绍了空间均匀场和空间不均匀场下的粒子对产生的情况。第一种情况主要介绍双脉冲结构振荡电场中电子-正电子对的产生、强双频振荡电场中非微扰电子-正电子对的产生、频率调制的激光场中电子-正电子对的产生和Dirac真空对啁啾外场的快速分辨。第二种情况主要介绍优化空间局域电场提高粒子对的产生率、多个势阱-垒结构的振荡场对粒子对产生的增强、振荡 Sauter 电势中正负电子对产生的问题、操纵Dirac真空以控制其在场诱导下的衰变、作为信息传输介质的Dirac真空还有正负电子对产生中的相干和非相干啁啾机制的转变。     

Probing the semi-macroscopic vacuum by higher-harmonic generation under focused intense laser fields

The invention of the laser immediately enabled the detection of nonlinear photon–matter interactions, as manifested for example by Franken et al.’s detection of second-harmonic generation.     

强激光与柱腔靶作用下准直高能电子束的产生

利用二维PIC粒子模拟程序研究了超短超强激光脉冲与柱腔靶相互作用产生的表面超热电子加速现象。采用光强为1021 W/cm2量级的超高斯激光脉冲掠入射进入柱腔靶,在靶的内壁上观察到了GeV量级的表面超热电子。超热电子束被准静态的电场和磁场约束在内壁表面附近,保证了电子束的准直性,发散角仅为1.6;并且由于超热电子束在纵向激光电场中加速了mm级的距离,激光到高能电子（100 MeV）的转换效率达到了26.6%。另外,通过多参数模拟和理论解析讨论了激光的光强以及横向空间分布对这种表面超热电子加速的影响。     

超短超强激光与Cu靶相互作用中质子背向发射的实验测量

 在20TW激光器上进行了超短超强激光与金属Cu膜靶的相互作用实验，当靶厚度不同时，采用CR39核径迹探测器测量了质子发射的空间分布和产额；使用Thomson磁谱仪测量了靶背法线方向质子束的能量分布。测量结果表明：质子产额为10 ⁵～10 ⁶每发；质子束沿靶背法线方向发射，与入射激光方向无关，并且存在较小的发射立体角，在一定能量处出现截止，截止能量的大小与靶厚度有关。     

Quasi-static electromagnetic pulse generated by ultra-intense laser pulses

A solitary structure of quasi-static electromagnetic pulse is formed in moderate density plasmas by a propagation of ultra-intense and ultra-short laser pulse, which is formed after the laser pulse is depleted and slowly propagates in the laser propagation direction. The structure is sustained by huge magnetic pressure and compensating electric field which are in an electromagnetic equilibrium together with the plasma motion. The solitary structure is formed when the resonance condition is satisfied and laser intensity is high enough to induce huge magnetic field pressure.     

超强短脉冲激光在不同密度分布等离子体中的自聚焦

讨论高斯型强激光束在具有初始柱对称密度分布的低密度冷等离子体中传播时，等离子体密度分布的不同对激光自聚焦的影响.推导出可以判断更有利于自聚焦发生的评价函数，这样通过比较不同密度分布的评价函数值就可以判断哪种密度分布更有利于自聚焦的发生.为了说明这种方法的有效性，对评价函数进行分析得出：在相同的激光场中等离子体柱的轴心密度给定时(以激光的光轴为轴)，离轴越远的地方密度越大及密度变化越陡，自聚焦越容易发生；相对论效应与有质动力共同作用比相对论的单独作用，自聚焦更容易发生.数值模拟证实了评价函数能准确的预测在不 关键词： 自聚焦 相对论效应 有质动力 评价函数     

Uncertainties in the hadronic contribution to the QED vacuum polarization

We describe an updated evaluation of the hadronic contribution to the QED vacuum polarization. It is obtained from a dispersion integral over the measured cross section ofe ⁺ e ^?→hadrons.     

Stationary vacuum fields with cylindrical symmetry

It is demonstrated that a stationary vacuum field solution with cylindrical symmetry is always reducible to a static cylindrically symmetric solution.