ON DYNAMIC EFFECTS IN COHERENT X-RADIATION OF RELATIVISTIC ELECTRON IN BRAGG SCATTERING GEOMETRY

摘要

Analytical expressions for spectral-angular distribution of parametric X-radiation (PXR) and diffracted transition radiation (DTR) of relativistic electron crossing a single crystal plate in Bragg geometry are derived on the basis of two-wave approximation of dynamic diffraction theory [1]. The expressions for the general case of asymmetrical reflection of relativistic electron Coulomb field on the plate are obtained. It was shown that in this geometry the essential increase of PXR angular density is possible due to a dynamic effect of PXR spectrum broadening just as in Laue geometry [2]. The considered Bragg geometry is interesting because of an interference effect of extinction, as the wave vector becomes complex even when an absorption is absent, and then the incident wave energy is transferred into reflected wave. A frequency region where the extinction effect manifests itself is named "region of total absorption". It is shown that decrease of the angle of electron incidence to the plate under fixed Bragg angle (asymmetric change) gives rise to a considerable increase of DTR angle density. The possibility of dynamical Borrmann effect manifestation in PXR and DTR for a thick single crystal is also considered in this work. It is shown that by the change of reflection asymmetry one can create such conditions in which the length of the electron path in the plate becomes small enough to neglect the electron multiply scattering, and the length of photon path exceeds the photo absorption length resulting in a bright manifestation of Borrmann effect in PXR.