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题名	基于激光等离子体量子电动力学效应的伽马辐射的研究
作者	刘琛
文献子类	博士
导师	沈百飞
关键词	量子电动力学效应 Quantum Electrodynamics Effect 伽马辐射 Generation of Gamma-ray Radiation 超强激光与等离子体相互作用 Ultra-intense laser-plasma interactions
其他题名	High-quality Gamma-ray Generation from Laser-plasma Interactions in the QED Regime
英文摘要	随着激光技术的飞速发展，激光的强度得到了显著的提高，正在建设的10PW激光装置有望提供10^22W/cm2甚至更高的激光强度。在这样的极端条件下，激光与等离子体的相互作用将进入量子电动力学（QED）区域。在这一区域中，伽马光子和正负电子对的产生是最为引人关注的现象。同时，由于QED效应（量子效应、辐射反作用力效应等）的出现，经典的辐射理论需要加以修正和补充，才能准确地描述带电粒子，特别是电子的辐射过程。可以，量子电动力学区域下激光与等离子体的相互作用为产生高品质的伽马辐射源提供了一种新的可能，因此这也逐渐成为近几年来研究的热点。本论文围绕如何产生这样的伽马辐射源、提高伽马辐射源的品质、增加伽马辐射源的特性，做了以下三个方面的工作： 1. 在非线性介质中，通过吸收多个低能量的光子，继而辐射出一个高能量光子，这一过程被称为高次谐波的产生。它可以发生在非线性晶体、气体和相对论等离子体中。然而，当激光光强到达10^22W/cm2时，量子电动力学效应开始出现，这一效应将随着光强的增大变得越来越显著，并在高次谐波的产生过程中发挥重要的作用。研究发现，在QED效应影响下，高次谐波呈现出非相干的特性，这与传统的相干的高次谐波有着本质的不同。基于此，我们将传统的相对论高次谐波拓展到QED区域，并将这种非相干的高次谐波命名为“QED谐波”。根据粒子模拟程序的结果，我们报道了一种利用“QED谐波”机制产生周期性的、超短的伽马脉冲链的方案。 2. 携带角动量的粒子也叫做涡旋的粒子。它在量子信息、微操控等领域有着广泛而重要的应用。迄今为止，国内外已经提出可以产生涡旋的电子、中子以及低能的光子。然而，涡旋的高能伽马光子的产生还鲜有报道。利用超强的涡旋激光和固体等离子相互作用，我们提出一种产生携带角动量的高能伽马光的方案。通过和固体靶的作用，涡旋激光的角动量首先转移给电子，电子通过量子辐射，再将角动量进一步转移给光子。由于所产生的伽马辐射的能量密度与入射涡旋光的拓扑荷、手性以及载波包络相位有关，因此，这也提供了一种对超强涡旋激光测量的新手段。 3. 基于激光等离子体相互作用的伽马辐射源，因其造价低、可调谐、易集成的优点，被认为是新型辐射装置发展的方向。目前，利用激光有质动力直接加速电子所产生的伽马光的准直性一直难以提高，这在很大程度上限制了伽马辐射源的应用。近几年，科研人员提出利用预制的特殊靶结构来解决这一问题，但复杂的靶结构也给实验增加了难度。然而，如果利用空泡加速机制代替有质动力直接加速，电子束的准直度可以得到显著提升，从而产生高品质伽马辐射。基于这一思路，我们提出一种产生高亮度、优准直、高能量的伽马辐射源的方案。研究表明，利用一束强度为3.84×10^23W/cm2的圆偏振激光与近临界密度等离子体作用，可以产生亮度高达7.2×10^24photons/s/mm2/mrad2/0.1%BW，发射度约为1.2mm·mrad，截止能量高达10GeV的伽马辐射。; With the rapid development of laser technology, the intensity of the laser has been greatly improved. The undergoing 10PW laser facilities are expected to reach 10^22W/cm2 or even higher intensities. Under such extreme conditions, the interactions between the ultra-intense laser and the plasma enters the quantum electrodynamics(QED)regime. In this regime,the copius generation of gamma-ray photons and the electron-positron pairs is the most prominent phenomenon, which has attracted great attention.At the same time,QED effects such as the quantum effect and the radiation reaction effect emerge in this regime,so that the classical radiation theory needs to be modified and revised in order to describe the radiation process of the charged particles correctly.Laser-plasma interactions in the QED regime have opened new opportunities for generating high-quality gamma-ray radiation,therefore it has been a very hot topic in the past few years. This thesis is consist of three parts,all of which are centred on the generation of high-qualtity gamma-ray radiation in the QED regime. 1. In nonlinear media,photons may combine into a photon of energy and momentum of all those photons. This process,called high-order harmonic generation,happens in nolinear crystal,gas and relativistic plasma. When the laser intensity reaches 10^22W/cm2,QED effects appear and play a significant role in the harmonic generation. In contrast to the gas and relativistic high-order harmonic generation processes,harmonics influenced by QED effects are usually not coherent because of the characteristic of random radiation,while the property of high intensity and ultra-short duration is conserved. In this sense, we extend high-order harmonic generation into the QED regime and term this incoherent harmonics in this regime as “QED harmonics” in order to distinguish it from the classical coherent HHG process. According to the results of the particle-in-cell simulations,we report a scheme of generating ultra-short gamma-ray train with periodic structures based on the “QED harmonics”. 2. Particles containing orbital angular momentum(OAM)are also called vortex particles,which are widely applied in the fields of micromanipulation,quantum information,imaging and astrophysics. So far,the generation of vortex particles such as electrons,neutrons and photons of low energy(<1MeV) have been studied theoretically and experimentally. However,gamma-ray photons of high energy(>1MeV) carrying the OAM have not been realized. Based on the laser-plasma interactions, we propose a scheme to generate high-energy gamma-ray photons with an OAM by irradiating a circularly polarized Laguerre–Gaussian laser on a thin plasma target. The spin angular momentum and OAM are first transferred to electrons from the driving laser,and then the OAM is transferred to the gamma-ray photons from the electrons through quantum radiation. This scheme has been demonstrated by using three-dimensional quantum electrodynamics particle-in-cell simulations. The topological charge, chirality, and carrier-envelope phase of the short ultra-intense vortex laser can be revealed according to the energy distribution of gamma-ray emission. Therefore, this can provide a helpful tool for detecting the incident ultra-intense vortex laser. 3. Gamma-ray radiation sources based on laser-plasma interactions are superior for its low cost, wide tunability and easy compactness. Therefore, it is regarded as one of the most promising aspect in the next-generation gamma-ray radiation facilities. But it is still difficult to generate a well-collimated gamma-ray radiation in the QED regime, which limits its applications in many fields. Recently, several proposals are reported to improve the collimation to some extent, where pre-formed plasma channel or cone-capillary structure are used. But these complex structures may add more difficulties in the experiments. However, if the electrons are accelerated by the laser-wakefield acceleration instead of direct-laser-acceleration by the ponderomotive force, the collimation of the electrons will be greatly improved, which will be helpful for high-qualtity gamma-ray generation. In this work, we propose a scheme to generate a bunch of ultra-bright, well-collimated, GeV gamma-ray photons from a circularly polarized laser with an intensity of 3.8×10^23W/cm2 illuminating on a near-critical-density(NCD) plasma. Particle-in-cell simulation shows that the generated gamma-ray photons have a brightness of 7.2×10^24photons/s/mm2/mrad2/0.1%BW, emittance of 1.2 mm?mrad and maximum energy near 10GeV.
学科主题	光学
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/30948]
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	刘琛. 基于激光等离子体量子电动力学效应的伽马辐射的研究[D].

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