【作者】 陈钊；

【导师】 霍裕昆； 孔青； 王平晓；

【作者基本信息】 复旦大学 ， 粒子物理与原子核物理， 2006， 博士

【摘要】 随着强激光技术的迅猛发展，研究利用激光的超强电磁场加速电子，并据此发展新一代小型化高能加速器已受到人们普遍关注。其中，我们研究小组提出了一种新的真空激光加速机制：俘获加速机制(CAS--Capture and Acceleration Scenario)。本论文重点研究了真空激光加速的几个关键课题：激光场的相速度、被加速电子的能量-角度关联、在真空激光加速中使用静磁场，并进一步将这些结论应用到俘获加速机制中。首先，我们研究相速度，因为相速度在真空激光加速中起着关键作用：位相匹配。我们组首次发现了真空传播的高斯激光束存在低相速度区，这是构成俘获加速机制的核心条件之一。所以我们深入研究了相速度，在经典波动方程的基础上，推导出一个全新的、适用于在均匀介质中传播的波的相速度表达式，并引伸出两个推论。新表达式和推论的核心在于相速度是波的振幅的表达式，对于单频率波来说，相速度可以完全用振幅表示，同时我们证明了低相速度区和高相速度区并存的普遍性，并给出了相应的判断依据。根据公式，我们提出了一个新的、更方便的测量和构造相速度分布的方法。其次，我们研究了真空激光加速的另一个关键问题：被加速电子的能量角度关联。其中最重要的一点是，通过经典Compton散射我们得到在平面波中电子的能量与角度是一一对应的，然而在实际激光束中，因为纵向电场的存在，该对应关系被破坏，也就是说相同能量的出射电子将会有一个角分布。我们导出了这种关系的表达式，发现这种特性对所有真空激光加速都适用，因为它源自于电子和光子的量子特性，也是聚焦激光的结构特性导致的。包括俘获加速机制在内的一些真空激光加速机制，要求注入电子的入射角度很小，这导致了电子会与用于聚焦的抛物面镜碰撞。为此，我们提出了一个解决方案：在真空激光加速中使用静磁场。研究表明，只需要加上一个几百高斯的静磁场，就可以偏转注入电子避免碰撞。研究进一步表明，当电子离开焦斑附近的强场区后，外加静磁场将会破坏电子在激光场中加速和减速的对称性，从而使被加速的电子获得更高的能量。这些研究给出了真空激光加速的一些重要特性，它们不仅是重要的基础理论研究课题，而且对相应加速机制实验方案的设计有重要意义更多还原

【Abstract】 With the rapid development of ultra-intense laser technologies, there has been much interest in the study of making use of intense laser fields to accelerate electrons in order to develop new generation of high energy laser-driven accelerators. Our group has proposed a new vacuum laser acceleration scheme, which we call the capture and acceleration scenario (CAS). In this thesis, emphasis has been paid on three key subjects for vacuum laser acceleration, i.e. phase velocity of the laser beam, the correlation between the outgoing energy and the scattering angle of the accelerated electrons, and using static magnetic field in the acceleration. We also apply these results for the case of CAS.We begin with the study of phase velocity, because it plays a key role in vacuum laser acceleration where phase matching is essential. Our group found subluminous phase velocity region in Gaussian laser beam propagating in vacuum for the first time, which is the primary condition for CAS. Along this line, an exact formula with two deductions for the phase velocity of a wave field in homogeneous medium has been derived from the fundamental wave equation. The core of these formulae is that the phase velocity is sufficiently determined in terms of the wave amplitude. The formulae also verified the general existence of subluminous and superluminal phase velocity region, as well as the judgment condition for them. It offers a new and relatively simple method to measure and control the phase velocity distribution.Then, we proceed to investigate another crucial subject of vacuum laser acceleration—the correlation between the outgoing energy and scattering angle of accelerated electrons. Essentially, the single-valued function of the correlation, derived from classical electrodynamics Compton scattering for a plane wave, is now broadened to become a band for the case of realistic laser beam, because of the existence of the longitudinal electric field. It means electrons with the same outgoing energy will have an angular spread. An equation to describe this correlation has been derived. It shows that these features are intrinsic to all vacuum laser accelerationsbecause they stem from the quantum characteristics of electrons and photos, as well as the structure of focused laser beams.For some vacuum laser acceleration schemes, including CAS, electrons have to be injected in a small crossing angle with laser beam, which may cause collision of electrons with parabolic mirror using for laser focusing. To solve the problem, we propose to apply static magnetic field in the acceleration. Our study shows that using static magnetic field with intensity of several hundred Gs can deflect effectively the electron trajectory and avoid the collision. What’s more, the applied magnetic field can break the symmetry of acceleration and deceleration, when the electrons have left the focal area, and raise the energy gain of the accelerated electrons.The above studies have presented crucial features for laser fields and vacuum laser accelerations. They are not only important from the fundamental research view, but of significance for experimental design to test the vacuum laser acceleration schemes as well.更多还原