Laser Driven Electron‐Positron Pair Creation–Kinetic Theory Versus Analytical Approximations

The dynamical Schwinger effect of vacuum pair creation driven by an intense external laser pulse is studied on the basis of quantum kinetic theory. The numerical solutions of these kinetic equations exhibit a complex time dependence which makes an analysis of the physical processes difficult. In particular, the question of secondary effects, such as creation of secondary annihilation photons from the focus spot of the colliding laser beams, remains an important open problem. In the present work we, therefore, develop a perturbation theory which is able to capture the dominant time dependence of the produced electron‐positron pair density. The theory shows excellent agreement with the exact kinetic results during the laser pulse, but fails to reproduce the residual pair density remaining in the system after termination of the pulse. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Schwinger terms in 1+1 dimensions

Two different approaches — Källen’s and Brandt’s methods — for calculation of the Schwinger terms in the 1+1 dimensional Abelian and non-Abelian free current algebras are discussed. These methods are applied to calculation of the single and double commutators. The validity of the Jacobi identities is examined in 1+1 and 3+1 dimensions and in this way is given natural restriction on the regularization. It is shown that the Jacobi identity cannot be broken in 1+1 dimensions even using the regularization which fails in the 3+1 dimensional case. A connection between the Schwinger term and anomaly is shown in the simplest case of the Schwinger model.     

A nondiagrammatic calculation of the ρ parameter from heavy fermions

A simple nondiagrammatic evaluation of the nondecoupling effect of heavy fermions on the Veltman ρ parameter is presented in detail. This calculation is based on the path integral approach, the electroweak chiral Lagrangian formalism, and the Schwinger proper time method.     

激光脉冲在等离子体中的压缩分裂

通过数值求解一维非线性薛定谔方程,研究了圆偏振入射激光脉冲在初始密度范围为1/4到略低于1倍临界密度的等离子体中的自压缩和分裂现象. 提高等离子体密度和入射激光强度以及减小脉冲宽度可以在更短的传输距离获得有效的激光脉冲压缩,压缩后的脉冲半高宽度可达到初始脉冲半高宽度的1/35,甚至更小. 这种压缩是激光脉冲在等离子体中形成高阶孤子的过程中产生的,可以获得比在稀薄等离子体中更好的压缩比例. 数值计算的结果给出了该情况下激光脉冲在等离子体中自压缩后形成的高阶孤子分裂. 利用一维粒子数值模拟程序(particle-in-cell,PIC)也观察到了脉冲的压缩和分裂现象,得到了与数值计算一致的结果. 关键词： 非线性薛定谔方程 自压缩 脉冲分裂 粒子模拟     

Schwinger mechanism of electron-positron pair production by the field of optical and X-ray lasers in vacuum

The probability W of e ⁺ e ^?-pair production in vacuum by an intense time-varying electric field created by optical or X-ray laser is calculated. Two characteristic regions γ?1 and γ?1 of adiabaticity parameter γ are considered. With an increase in γ and on passing from monochromatic radiation to a finite laser pulse, the probability W increases sharply (for the same field intensity). The dependence of the probability W and the electron and positron momentum spectrum on the pulse shape is discussed (the dynamic Schwinger effect).     

强激光场中真空极化效应

 通过求解狄拉克方程,对强激光场下真空极化问题进行了研究。理论计算结果表明：在仅随时间变化的电场下,要激发狄拉克海中负能级的电子,需要两个阈值条件,即激光场的电场强度大于等于10¹⁶ V/cm和激光场的持续时间大于等于10^-21 s。前者主要保证负能态电子有足够的能量跃迁到正能态,后者主要是保证电子在跃迁过程中动量亏损得以补偿。     

时频分布技术在激光与等离子体相互作用粒子模拟诊断中的应用

在对超短超强激光与等离子体相互作用进行粒子模拟诊断的研究中,输出量普遍为时间或空间上的非平稳信号。将时频分布技术引入粒子模拟结果的诊断,指出用时频分布技术等现代信号处理技术诊断模拟结果中的非平稳信号具有重要意义。作为实例,考察了用线性啁啾激光打靶条件下,包含nc/4(nc为等离子体临界密度）的非均匀等离子体区域中的受激拉曼散射的演化,并用时频分布技术得到了清晰的物理图像。     

BJORKEN-JOHNSON-LOW TECHNIQUE AND PERTURBATION STUDY ON CHIRAL ANOMALY IN ABELIAN COSET PURE GAUGE FIELD THEORY

The perturbation theory in coset pure gauge field theory is studied for the first time in this paper.By using the Bjorken-Johnson-Low technique and calculating the Schwinger term in related commutators,the anomalous Ward identity in Abelian coset pure gauge field theory is derived,which is consistent with the non-perturbative calculation.     

VO2光学薄膜的脉冲激光损伤特性测试

为评价VO2光学薄膜在光电器件中的工作可靠性,搭建了可输出连续渐变激光能量密度的脉冲激光照射实验平台,运用1对1与s对12种激光损伤测试手段进行激光辐射照射实验,采用线性外推法和测量计算法2种方法对实验结果进行了处理并得出VO2薄膜在重复频率10 kHz、中心波长532 nm、脉冲宽度15 ps脉冲激光辐射下的损伤特性。结果表明:VO2薄膜损伤几率与脉冲激光的单脉冲能量密度呈线性关系,重复辐射的激光脉冲对VO2薄膜造成的损伤具有积累效应,且重复辐射的激光脉冲次数越多损伤积累效果越明显。     

A comparison of condensate mass of QCD vacuum between Wilson line approach and Schwinger effect

We studied the condensate mass of QCD vacuum through the duality approach via dilaton wall back-ground in the presence of the parameter c,which represents the condensation in a holographic set up.First,fromWilson line calculation,we found m₀²(i.e.,the condensate parameter in mixed non-local condensation),whose beha-vior mimics that of QCD.The value of m₀²that we found by this approach is in agreement with QCD data.Second we considered the produced mass m via the Schwinger effect mechanism in the presence of the parameter c.We show that vacuum condensation generally contributes the mass dominantly and that the produced mass via Schwing.er effect is suppressed by m₀.     

非链式脉冲DF化学激光器反应动力学模型

依据非链式脉冲氟化氘(DF)激光器的反应机理, 采用速率方程理论, 综合考虑了基态DF分子、D₂分子、D原子、F原子对激发态DF分子的消激发作用, 建立了非链式脉冲DF激光器反应动力学模型. 运用Runge-Kutta法对该模型进行数值计算, 得到了增益区内各组分粒子数密度随时间的变化关系. 进而运用该模型研究了工作气体配比和输出镜反射率对DF激光器腔内光子数密度、 单脉冲能量、脉冲宽度和输出功率的影响, 得到了最佳气体配比和最佳输出镜反射率参数. 采用放电引发方式对非链式DF激光器进行了实验研究, 实验测得脉冲波形及单脉冲能量与速率方程理论模型计算结果基本一致. 本文的研究结果可为非链式脉冲DF激光器的优化设计提供理论参考. 关键词： 脉冲DF激光器 动力学模型 速率方程 数值计算     

Quantum corrections to instanton calculations in the Abelian Higgs model

In the (1+1)-dimensional Abelian Higgs model we calculate the final state quantum corrections to the fermion number violating cross-section in the background of the instanton. The arising determinants are treated in the Schwinger proper time formalism using some refined approximation techniques which are controlled in several ways and are also applied to the well known case of the quantum double well for comparison.     

R~4 corrections to holographic Schwinger effect

We consider R4 corrections to the holographic Schwinger effect in an AdS black hole background and a confining D3-brane background. The potential between a test particle pair are performed for both backgrounds. We find there is no potential barrier in the critical electric field, which means that the system becomes catastrophically unstable. It is shown that for both backgrounds, increasing the inverse 't Hooft coupling parameter 1/λ enhances the Schwinger effect. We also discuss the possible relation between the Schwinger effect and the viscosity-entropy ratioη/s in strong coupling.     

Relativistic quantum statistical mechanics in two-dimensional space-time

We construct for a boson field in two-dimensional space-time with polynomial or exponential interactions and without cut-offs, the positive temperature state or the Gibbs state at temperature 1/β. We prove that at positive temperatures i.e. β<∞, there is no phase transitions and the thermodynamic limit exists and is unique for all interactions. It turns out that the Schwinger functions for the Gibbs state at temperature 1/β is after interchange of space and time equal to the Schwinger functions for the vacuum or temperature zero state for the field in a periodic box of length β, and the lowest eigenvalue for the energy of the field in a periodic box is simply related to the pressure in the Gibbs state at temperature 1/β.     

The quenched approximation in some two-dimensional field theories

We investigate the effect of suppressing closed fermion loops (the quenched approximation) in some (1 + 1)-dimensional field theories. In the Schwinger and Thirring models we find that effects of fermion loops on bound state masses can be absorbed in a rescaling of the coupling constant. In the Schwinger model an extra (decoupled) massless ghost appears and the order parameter $\text{〈}\text{ψ}\text{ψ〉}$ becomes infrared divergent. In an extension of the Schwinger model we compute effective lagrangians for the bound state spectrum in the quenched and unquenched case that look rather different.     

THE GENERALIZED MASTER EQUATION THEORY OF ELECTRON SCAVENGING IN AMORPHOUS SOLIDS

Electron scavenging in amorphous solids is analyzed by using diffusion controlled reaction model. In terms of stochastic process theory, the process is an age-dependent branching process which is described by linear death process of generalized master equation.The variation of number of trapped electron with time, N(t), is calculated with Ngai's fractional exponential waiting time density for the time between hops. Quantitative comparison with Miller's pulse radiolysis experiments on frozen 6M NaOH is made and the agreement is fairly well. The rigour and simplicity in mathematics of the generalized master equation method developed here are in sharp contrast to the master equation method in which quantitative calculation can hardly be done.     

Schwinger's method for the fermionic Casimir effect

The Casimir energy of a massive Dirac field confined between two parallel infinite plates is computed using a method proposed by Schwinger. The massless case is obtained as a limit of the massive case. The boundary conditions are those of zero current through the plates, as inspired by quark confinement in the MIT bag model for hadrons. We use an analytical continuation method of regularization which allows the employment of Epstein function techniques. The calculation using Schwinger's original regularization by a cutoff in proper time is also outlined.     

非线性啁啾频率对势阱产生正负电子对的增强

用计算量子场论方法研究了非线性啁啾频率对势阱中正负电子对产生的增强效应。研究了由静态势阱和动态势阱组成的组合势阱中产生的正负电子对的密度、产额和能谱等性质随着啁啾参数的变化,分析了组合势阱的频谱和瞬时束缚态。发现非线性啁啾效应对低频区域比较敏感,与固定频率情况相比可以使粒子数增加2～3倍。与组合势阱相比,非线性啁啾效应对单个振荡势阱更敏感。在低频下单个振荡的势阱中正负电子对产额可提高多个数量级。这是因为在低频下单个振荡的势阱中,主要通过量子隧穿过程产生的正负电子对数目非常低。非线性啁啾效应增加了高频场成分,提高了多光子过程和动力学辅助机制。由于高频抑制作用,所以非线性啁啾效应对高频区域粒子的增量不大,甚至会抑制正负电子对的产生。     

在相对论性激光-等离子体系统中初始物理参数对激光脉冲的影响

基于相对论性激光-等离子体动力学理论，研究了相对论性激光-等离子体系统中圆偏振入射脉冲激光和等离子体相互作用对激光脉冲宽度的影响. 具体分析了在不同初始物理参数下脉冲激光的脉冲宽度在等离子体传播过程中的变化情况，重点分析了激光脉冲在等离子中压缩. 计算结果表明增加入射激光的强度和入射脉冲宽度以及减小等离子体的初始密度，能够有效地实现脉冲宽度在等离子体中压缩；当激光脉冲的初始参数a₀=0.12和τ=70以及等离子体密度n₀=0.3时，脉冲宽度相对压缩T/τ接近于1/10，从而给出了激光压缩的理论优化参数. 关键词： 相对论性激光-等离子体 激光脉冲宽度 等离子体密度 自压缩     

激光烧蚀脉冲放电激发的土壤等离子体电子数密度和温度的研究

以激光烧蚀快脉冲放电激发土壤为例,研究了激光烧蚀快脉冲放电等离子体技术产生的土壤等离子体的电子数密度和温度。根据实验测得的Si原子和离子谱线的强度和萨哈玻尔兹曼方程,计算了等离子体的电子温度,并从分析Si I 250.69nm谱线的斯塔克展宽中导出了等离子体的电子数密度。与使用同样激光能量激发的激光等离子体相比,激光烧蚀快脉冲放电激发等离子体的电子数密度和温度都明显增加,与观察到的光谱信号强度是一致的。