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题名	相对论激光与等离子体相互作用中的电子加速及角动量问题研究
作者	张林港
文献子类	博士
导师	沈百飞
关键词	相对论激光与等离子体相互作用 relativistic laser-plasma-interaction 涡旋光 vortex laser CO2激光 carbon-dioxide laser 电子加速 electron acceleration 反射定律 optical reflection law 麦克斯韦电磁应力 Maxwell electromagnetic stress
其他题名	Relativistic laser-plasma-interaction: Electron acceleration and the orbital angular momentum
英文摘要	自1960年梅曼（T. Maiman）成功研制出世界上第一台激光器开始，激光与物质的相互作用就是人们一直致力研究的核心物理问题之一。上世纪90年代，啁啾脉冲放大技术的发明给人们提供了前所未有的超短超强极端光场条件，实验室已经能够获得聚焦强度超过10^22 W/cm^2、单脉冲宽度小于10 fs 的激光脉冲，如此强的激光可将物质迅速电离形成等离子体，光与物质的相互作用进入强相对论非线性光学领域。其中，利用800 nm 左右波长的激光驱动等离子体尾波作为加速媒介的电子加速方案日臻完善，目前人们已实现能量高于4.2 GeV的电子束，并能够通过裁剪等离子体密度、控制电子束注入等手段对电子束的能散度、发散度等品质参数进行精确的控制。近年来，具有10.6 u m波长的短脉冲CO2激光已可达到相对论强度且被成功应用到粒子加速中。另一方面，自Allen等人提出具有形如exp(il?)角向相位的涡旋光束会携带轨道角动量以来，人们对于涡旋激光脉冲的研究兴趣持续不减，尤其是产生具有相对论强度涡旋光的方案在最近被提出，相对论强度涡旋光与等离子体的相互作用迅速成为一个新的研究热点。得益于这些光场模式的迅速发展，本论文着重研究相对论涡旋激光和相对论CO2激光与等离子体的相互作用，主要做了以下方面的工作： 1. 在相对论涡旋激光与等离子体相互作用领域发现了不符合传统光学反射定律的全新现象，对反射定律做出了重要修正。经典光学认为，光在介质平面反射时，入射光、法线和反射光在同一平面内，且反射角等于入射角，而对于相对论强度的涡旋激光光束，这一基本原理面临新的挑战，相对论涡旋激光和等离子体的相互作用具有全新的非线性传输特征。三维数值模拟表明，当一束相对论强度的涡旋光斜入射等离子体靶面时，其反射光束偏离了入射平面。由于涡旋激光具有角动量，因此其在靶面的反射类似于高速侧旋的乒乓球在撞击拍面后的反弹过程。采用普适的麦克斯韦应力张量描述该相互作用过程中的电磁作用力，数值模拟和理论分析均表明，涡旋光的应力张量具有不对称的切应力分量，挤压等离子体靶面使得靶表面的旋转对称性被破坏，从而导致了反射光偏离入射平面。该不对称切应力张量和涡旋光的拓扑电荷l有关，是涡旋光的一个内凛特征，在相对论涡旋光与物质相互作用中起着非常重要的作用。 2. 提出了利用长波长CO2激光驱动低密度等离子体获得高品质电子束的理论方案。长波长的相对论CO2激光脉冲（激光的归一化振幅a=2.0）能够激发一个较大体积的空泡尾场，其具有较大的电荷容纳能力，能够加速更多的电子。采用一束横向传播的注入脉冲诱导和控制电子的注入过程。Particle-in-cell数值模拟可以得到总电荷量达10 nC、绝对能散小于16 MeV的电子束，从而该电子束单位能量间隔内的电荷量可达0.6 nC/MeV。高强度的CO2激光驱动的电子加速机制为高电荷量、低能散电子束的产生提供了一种新途径，得到的电子束可应用到X射线产生等很多人们感兴趣的方面中去。; Light-matter interaction is always being one of the critical concerns in physics since the first laser’s coming out in 1960 by T. Maiman. By 1990s, the invention of chirped pulse amplification technique offered ultra-short and ultra-intense laser field conditions that had never been realized before. Nowadays, lasers with focal intensity above 10^22 W/cm^2 and duration of single pulse shorter than 10 fs has been achieved in laboratory. Matters under this laser condition will be promptly ionized into plasmas, leading the interaction of the electromagnetic field and the plasma well into the relativistic nonlinear optic regime. Being proposed nearly 40 years ago, the wakefield acceleration, driven by intense laser with wavelength of around 800 nm, has been sufficiently developed both in theory and in experiment. Controlling the energy dispersion and emittance of the electron beams by tailoring the plasma density and other control injection methods has been explored. Recently, electron beams with energy as high as 4.2 GeV was realized. In addition, short pulse CO2 laser has approached a terawatt power and has been applied successfully for driving particle acceleration. On the other hand, discovered by Allen et al. in 1992, the vortex laser pulse with phase-dependence of exp(il?) is attracting continuous attention in various aspects. Recently, the aspiring proposal of producing relativistic intense vortex laser kindled a new interests to the relativistic vortex laser matter interaction. Motivated by the above achievements, in this thesis we explore the relativistic vortex and relativistic CO2 laser plasma interaction. Specific results are given as follows: 1. An interesting deflection effect deviating the optical reflection law is revealed in the relativistic regime of intense vortex laser plasma interaction. When an intense vortex laser obliquely impinges onto an overdense plasma target, the reflected beam deflects out of the plane of incidence with an experimentally observable deflection angle. The mechanism is demonstrated by full three-dimensional particle-in-cell simulation as well as analytical modeling using the Maxwell stress tensor. The deflection results from the rotational symmetry breaking of the foil driven by the unsymmetrical shear stress of the vortex beam. The l-dependent shear stress, where l is the topological charge, as an intrinsic characteristic to the vortex beam, plays an important role as the ponderomotive force in relativistic vortex laser matter interaction. 2. High quality electron beam obtained from wakefield acceleration driven by relativistic CO2 laser in low-density plasma is demonstrated using particle-in-cell simulation. An intense CO2 laser pulse of long wavelength excites a wake bubble that has a large elongated volume for accelerating a large number of electrons before reaching the charge saturation limit. A transversely injected laser pulse is used to induce and control the electron injection. It is found that an electron bunch with total charge up to 10 nC and absolute energy spread less than 16 MeV can be obtained. As a result, the charge per energy interval of the bunch reaches up to 0.6 nC/MeV. Intense CO2-laser based electron acceleration can provide a new direction for generating highly charged electron bunches with low energy spread, which is of much current interest, especially for table-top X-ray generation.
学科主题	等离子体物理
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/30949]
专题	中国科学院上海光学精密机械研究所
作者单位	中国科学院上海光学精密机械研究所
推荐引用方式 GB/T 7714	张林港. 相对论激光与等离子体相互作用中的电子加速及角动量问题研究[D].

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