基于激光等离子体相互作用的辐射光源
文献类型：学位论文
| 作者 | 时银 |
| 学位类别 | 博士 |
| 答辩日期 | 2015 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 沈百飞 |
| 关键词 | 轨道角动量 X光辐射 激光等离子体 磁矩进动辐射 脉冲星 |
| 其他题名 | Radiation source based on laser-plasma interaction |
| 中文摘要 | 在量子理论中，每个光子携带的线性动量为 。对于圆偏振光子，每个光子也将携带 的自旋角动量(Spin Angular Momentum, SAM)。1992年Allen等人也首次提出具有角向相位依赖 的光束携带有轨道角动量(Orbital Angular Momentum, OAM)。在弱光下，携带OAM的涡旋光束已被广泛证实、产生、调控并得到了应用。通常使用涡旋相位透射晶体或光栅相位板来产生涡旋光。其应用包括量子纠缠实验、量子信息处理、光镊操作等。由于基于啁啾脉冲放大(Chirped Pulse Amplification, CPA）的激光模式基本趋于单一，OAM效应在相对论激光中一直未获得重视。本论文基于相对论强激光与等离子体相互作用，首次提出“光扇”（“Light Fan”）方案来获得相对论强度的涡旋光。进一步的研究突出了相对论强激光中角动量和强扭力的特性，为以后实验获得相对论涡旋光和极端条件下角动量效应提供了理论基础。除此之外，“光扇”等离子体也获得了反向的等量OAM。这为研究OAM在等离子体中的效应提供了基础。相对论激光除了具备交变的强电磁场外，也有随激光脉冲包络变化的有质动力。而激光与等离子体相互作用中，有质动力在等离子体中形成的静电分离场可以用来加速得到高能电子、质子源和辐射偏转力场。比如激光等离子加速器产生GeV高品质电子束用于驱动辐射源，等离子体空泡内部的betatron振荡辐射源等。相对论强激光的极端电场和极端磁场也使得在大型对撞机碰撞之外，也可以研究基本粒子在极端电磁场下的特性。比如辐射的反作用力，辐射中的spin效应，基本粒子参数的高精度测量等等。 本论文主要包括以下几个方向的工作： 1. 当携带高光子密度的相对论激光脉冲与特殊结构的固体靶相互作用时，涡旋形状的固体等离子体可以感受到高强度的扭力。我们称之为“光扇”方案。由于靶材的特殊结构，等离子体获得了显著的轨道角动量（OAM），同时反射光也获得了反向的OAM成为相对论涡旋激光脉冲。我们用PIC模拟和相关理论模型证实了这一过程，并强调了相对论涡旋激光所携带的强扭力和高角动量密度。这一产生相对论涡旋光的首次可行性方案，也让涡旋光驱动等离子体加速正电子、质子成为可能。相关实验也在进行并取得突破性进展。 2. 激光等离子体加速器（Laser-plasma accelerators, LPAs）已经可以产生能量为GeV、脉宽为fs、归一化发散度为 mm mrad、电荷量为几百pC的高品质电子束。但能散度一直未能达到传统加速器的品质。基于已有的电子束参数，利用激光与固体等离子体产生的静电分离场为电子束提供偏转力可以得到新的高亮度、宽频谱X光光源。我们称之为TNSF-kick方案。靶后鞘层场（Target Normal Sheath Field, TNSF）垂直靶材表面，其强度可以在 的尺度维持 V/m的量级，通常用于质子加速。但相对高能电子传播方向倾斜放置靶材就可以提供高强度的横向电场分量，从而辐射出高能光子。充分利用LPAs的优势(即高电荷、高能和低发散度)，该方案可以得到亮度为1022 光子/(s mm2 mrad2 0.1\%BW)、脉宽为10fs的宽能谱（0.1 MeV to 4 MeV）X光光源。这比采用背向汤姆逊散射方案得到同样宽频谱，要在亮度上高两个量级。该光源有望在超快Laue衍射实验中得到应用。 3. 在麦克斯韦理论中，辐射除了可以来自电荷外，也可能来自磁矩的进动。同电荷一样，作为基本粒子本质属性的自旋磁矩也可能提供辐射。在量子理论中，这一辐射主要与自旋翻转有关。脉冲星作为中子星的一种，持续性地发射出周期性信号。其中频谱包括射频、可见光、X光和伽马光。基于加速电子辐射机制的模型并未完全解决诸如射频辐射源、射频相干性、射频频谱分布等特性。在该工作中，我们基于磁矩进动辐射机制，提出了一个新的射频辐射模型来解释上述脉冲星辐射特性。这里射频辐射被最终归结到脉冲星内部中子的自旋磁矩而不是电荷。射频辐射源、脉冲产生机制、射频相干性、频谱分布的光子指数以及 图中观测到的射频脉冲星的分布都在模型中给出了解释。同时也对静默脉冲星进行了合适的预测，期望在未来的观测中能够得到验证。例如，更多静默脉冲星期待未来在 图中的射频脉冲星分布区域的边界被发现。 |
| 英文摘要 | In quantum theory, every photon carries a linear momentum equivalent to and, if circularly polarized, a spin angular momentum (SAM) of . In 1992, Allen et al. recognized that light beams with an azimuthal phase dependence of carry an orbital angular momentum (OAM). In nonrelativistic regime, twisted light with OAM has been widely realized, tuned and applied. Usually, a spiral phase plate is used for twisted light creation. Applications include quantum entanglement, quantum information and optical tweezers etc. Because of the single mode of laser based on chirped pulse amplification (CPA), OAM effects in relativistic laser haven’t been studied. This thesis first proposed a scheme of “Light Fan” to get relativistic twist laser. It is based on laser plasma interaction. The further researches emphases on the ultrahigh OAM density and strong torque, which are theoretical basis for relativistic twisted laser creation in laboratory and OAM effects studies in extreme conditions. Besides that, the plasma of “Light Fan” can also get the opposite OAM. It makes the study of OAM effects in plasma possible. Relativistic laser has strong ponderomotive force due to envelope distribution as well as pulsed and alternating huge electric and magnetic field. In relativistic laser plasma interactions, the ponderomotive force can makes strong electrostatic field in plasma. This strong field can be used for high electron beam acceleration, high energy proton beam acceleration and also the acceleration field of radiation source. For example, GeV electron beam can be accelerated in laser plasma accelerators (LPAs) and electrons in plasma bubble can have betatron oscillation which gives strong radiation. For basic particles, pulsed and alternating huge electric and magnetic field can also provide some extreme conditions. It can gives an alternative tools beside the large particle accelerators and colliders. The related researches can include radiation reaction force, spin effects in radiation and high precise measurement of basic parameters. Specific results in this thesis are follows: 1. When a relativistic laser pulse with high photon density interacts with a specially tailored thin foil target, a strong torque is exerted on the resulting spiral-shaped foil plasma, or “light fan”. Because of its structure, the latter can gain significant OAM, and the opposite OAM is imparted to the reflected light, creating a twisted relativistic light pulse. Such an interaction scenario is demonstrated by particle-in-cell (PIC) simulation as well as analytical modeling, and should be easily verifiable in the laboratory. As important characters, twisted relativistic light pulse has strong torque and ultra-high OAM density. It also makes the acceleration of positrons and protons using relativistic LG laser possible. Related experiments are making some breakthroughs. 2. LPAs can provide electron beams with GeV energy, fs pulse width, mm mrad normalized emittance and hundreds pC of change. But the energy spread is always bigger than electron beam from conventional accelerators. Based on electron beam from LPAs, electrostatic field due to laser interaction with foil can provides huge bending force. It can gives a compact ultra-bright, ultra-broadband hard X-ray source. Target normal sheath field (TNSF) can be V/m over a scale of , which is perpendicular to the surface and is usually used to accelerate protons. When the foil is put oblique to the electron beam propagation direction, electrons will be kicked transversely and radiate high energy photons. Fully utilizing the advantages of electron beam from current LPAs (high charge, high energy, and low emittance), this X-ray source has a high peak brightness in the order of 1022 photons/(s mm2 mrad2 0.1\%BW), an ultrashort duration (10 fs) and a broadband spectrum (flat distribution from 0.1 MeV to 4 MeV). The peak brightness of our scheme can be two orders higher than the highest brightness that Thomson scattering can provide over the same broadband spectrum. It has wide-ranging potential applications, such as in ultrafast Laue diffraction experiments. 3. In Maxwell theory, radiation can comes from magnetic precession as well as charge particle acceleration. As the intrinsic character of basic particles, spin magnetic moment can be as important as charge in radiation. In quantum theory, radiation due to spin magnetic moment can be associated with spin-flip. As a kind of neutron star, pulsar can emits periodical radiation pulse. The radiation spectrum can covers radio, optics, X-ray and gamma ray. Radiation models of pulsar radiation based on charge acceleration still can’t explain some characters, like radio radiation source, radio coherence and radio spectrum etc. Based on magnetic moment precession radiation, we propose a new theory of pulsar radio radiation. Here radio radiation is connected to spin magnetic moment of neutrons inside a pulsar instead of charge. The radio radiation source, pulse production mechanism, coherency, photon index of spectrum and observed radio pulsar distribution in diagram are explained. Besides that, some predictions on radio-quiet pulsar are given. For example, more radio-quiet pulsars are expected to be discovered in the boundary of radio pulsar area in diagram. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15926]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 时银. 基于激光等离子体相互作用的辐射光源[D]. 中国科学院上海光学精密机械研究所. 2015. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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