Studies Of The Properties Of Vacuum Laser Acceleration

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.