COHERENT RADIATION FROM RELATIVISTIC ELECTRONS IN ORIENTED CRYSTAL

摘要

The main results of the theory of the coherent radiation by relativistic electrons in crystals are obtained in the approximation of a weak perturbation of the particle motion by a crystal lattice field. In this case the radiation of a particle in a crystal can be treated on the basis of the Born and semi-classical approximations of quantum electrodynamics as well as in the frames of the classical electrodynamics if one can neglect the radiation recoil. It is essential that all these approximations yield the same result for the coherent radiation spectrum if the particle trajectory is close to a straight line. The last condition is, however, quickly violated while decreaing the incidence angle of the particle on the crystal with respect to one of its crystal axes or planes. The particle motion in the periodic field of the crystal atomic string parallel to its direction may possess a very complicated pattern, specifically it may be regular as well as chaotic with respect to the atomic strings. It is clear that this must lead to the distortion of the interference effect in radiation obtained in the approximation of a rectilinear trajectory. Taking into account the complicated pattern of particle motion in a crystal it is vital to simulate the motion and coherent radiation of relativistic electrons in crystals. In the paper we stress that the account of the realistic dynamics of a particle motion inside a crystal at a small angle to one of its axes leads to a considerable distortion of spectrum characteristics of the coherent radiation that can be obtained in the assumption of a straight-line trajectory. It is essential that not only the radiation intensity but also the interference pattern of the radiation process undergo changes. It is extremely important to account these facts in the quantitative analysis of measured data.