相对论飞秒激光和自由电子以及等离子体相互作用研究
文献类型：学位论文
| 作者 | 何峰 |
| 学位类别 | 博士 |
| 答辩日期 | 2005 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 余玮 |
| 关键词 | 相对论飞秒激光脉冲 电子加速 能量增益 等离子体 |
| 其他题名 | The interactin of relativistic femtosecond laser pulse with a free electron and plasma |
| 中文摘要 | 随着飞秒激光技术的发展，激光和物质的相互作用掀开了崭新的篇章。当激光脉冲聚焦后，强度超过1018W/cm2，其电场趁过1012V/m，比传统加速器的电场高5-6个数量级。电子在如此强的电场中做相对论运动，橄光场在微米的长度范围内把电子加速到MeV以上，这可以应用于激光电子加速器。电子在激光场中作相对论运动的同时，伴随着高度非线性电磁辐射，可以产生短波长相干辐射源。本论文主要进行了激光加速电子和相对论电子辐射的研究工作，具体如下：1．研究了电子在平面激光场中的运动轨迹。当激光的强度a。＜＜1（ao＝1对应的激光的强度为I入2＝1．38x1018wll矶2／cm2）时，电子主要受激光电场驱动作横模运动；当。0＞＞1时，电子在有质动力作用下作纵模运动更为显著。在平面波脉冲作用下，电子被脉冲的上升沿加速，被脉冲的下降沿减速，电子不能从激光脉冲中获得净能量增益。给出了初始静止的电子、有一定初速度的电子以及电离电子在激光场中的运动轨迹。2．研究了紧聚焦的相对论飞秒激光脉冲在真空中对初始静止电子的加速。当激光脉冲的束腰半径小于电子在激光场中的纵向位移时，必须考虑激光脉冲和电子相互作用过程中脉冲束腰半径的变化。电子被脉冲上升沿加速时，激光脉冲的束腰半径小，强度大，对电子的加速效果显著；当激光脉冲的下降沿减速电子时，激光脉冲的束腰半径大，强度小，对电子的减速作用差。当电子和激光脉冲分离时，电子获得了能量增益。电子的能量增益和电子的初始位置以及激光的强度、束腰半径、脉宽都有关系。3．研究了聚焦激光脉冲对有一定初速度电子的加速。当电子有一定的初速度，并和激光同向传播时，电子和脉冲上升沿的作用时间和作用距离大大增加，电子被激光脉冲的卜升沿加速到极高的能量。当脉冲下降沿减速电子时，激光脉冲己经发散，强度很弱，减速作用几乎可以忽略不计。当电子和激光脉冲分离时，电子获得的能量增益大大增加。4．研究了平面波激光脉冲和电子相互作用导致的激光同步辐射现象。当电子具有合适的初速度，传播方向与激光的传播方向相反时，电子在激光脉冲中心作圆周运动。由于电子的运动半径比传统同步辐射环中电子的运动半径小了好几个数量级，因此电子的辐射能量大大增加。这样的电子可以作为有效的激光同步辐射源。另外，还研究了相对论飞秒激光脉冲和线性等离子体的相互作用。当激光强度较弱时，激光在线性等离子体中的光场分布可以用Airy函数来描述。但当光很强时，在等离子体内形成了一系列的"电子岛"和"电子空腔"。正负电荷的分离生成了静电场，一部分激光能量转化为静电能。用数值模拟的方法研究了激光和不同密度薄膜靶的相互作用。研究发现薄膜靶的密度太低，则激光能量几乎直接穿透靶；当靶的密度太高时，激光能量被靶反射。当激光强度为1019W/cm2，靶的密度为2．snc时，激光能量和靶祸合得较好，形成的静电场可以有效的加速离子。 |
| 英文摘要 | With the development of the ultra-short and ultra-intense laser technology, there are many new and interesting phenomena about the interaction of laser and plasma. When the laser intensity is higher than 1018W/crn2, the electric field can exceed 1012V/m. Electrons in such an intense field can be accelerated more than MeV. Because of the powerful radiation of the relativistic electron in the electromagnetic wave, the electron can be used as an ultra-short and coherent radiation source. Some results in this paper are given as follows: The electron trajectories in a plane electromagnetic are shown. When the laser intensity is weak, i.e, a0 << l(a0 = 1 corresponding to the laser intensity /A2 = 1.38 x 1018Wfim2/cm?), the movement is determined by the transverse oscillation. However, the longitudinal drift is primary as the laser intensity ao >> 1. Ponderomotive force driven acceleration of an electron at the focus of a high- intensity short-pulse laser is considered. Accounting for the asymmetry of accel eration and deceleration due to the evolution of the Gaussian laser beam waist, the energetic electron is extracted from the laser pulse by the longitudinal pon deromotive force. Final energy gain as a function of the scattering angle and the electron's initial position has also been discussed. With the development of photocathode rf electron gun, electrons with high- brightness and mono-energy can be obtained easily. By numerical solving the relativistic equations of motion of a electron generated from this facility in laser fields modelled by a circular polarized Gaussian laser pulse, we find the electron can obtain high energy gain from the laser pulse. The corresponding acceleration distance for this electron driven by the ascending part of the laser pulse is much longer than the Rayleigh length, and the light amplitude experienced on the electron is very weak when the laser pulse overtakes the electron. The electron is accelerated effectively and the deceleration can be neglected. 4. Electron with an appropriate initial velocity injected into an oncoming, ultra-intense circularly polarized laser pulse will execute circular relativistic motion at the peak of laser pulse. The circulating electron then radiates in the same manner as that in the storage ring of a conventional synchrotron source. Owing to the extremely small orbit radius, the laser-field synchrotron radiation thus generated can be a powerful source of radiation pulses at short wavelength and short duration. In additional, the interaction of relativistic femtosecond laser pulse with linear plasma is considered. The simulation and theory results are consistent. The ions keep immobile during the interaction because of its great inertia. Electrons are driven by the ponderomotive force, then a set of electron islands and cavities are formed in the linear plasma. Some laser energy transforms to electrostatic energy. Fast-ion generation in the interaction of a relativistic femtosecond laser pulse with different density plasma foils has been studied with fully relativistic 2D3V particle-in-cell (PIC) simulations. Simulation results show that there is a maximum for laser energy transformation versus plasma foil density. The ions get maximum energy gain when the foil density is about the critical density. The laser energy cannot couple to the target effectively if the foil density is too high or too low. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15586]  |
| 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 | 何峰. 相对论飞秒激光和自由电子以及等离子体相互作用研究[D]. 中国科学院上海光学精密机械研究所. 2005. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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