Veronika V. Soboleva

Coherent radiation of relativistic electrons in dielectric fibers in the millimeter wavelength range

The generation of visible light by a relativistic electron beam in dielectric fibers was considered in X. Artru and C. Ray, Nucl. Inst. Meth. B 309, 4 (2013), where the characteristics of radiation induced in a fiber by the electromagnetic field of a relativistic charged particle were studied and it was emphasized that they differ from those in the traditional mechanisms of radiation such as transition and diffraction. We have experimentally studied the characteristics of such a radiation in the millimeter wavelength range. It has been shown that radiation can be generated through different mechanisms depending on the geometry of the position of a fiber with respect to the trajectory of the charged particle. Fibers have been shown to be promising for nondestructive diagnostics of accelerator beams.

On the role of the surface currents in conducting targets in the formation of the diffraction and transition radiation of relativistic electrons

The surface current method and the pseudophoton method are widely used in the study of the interaction between relativistic electrons and matter. A simple analysis reveals the contradictions between these methods as to the excitation of the currents on the surface of the conducting target. To solve this contradiction, the surface currents on the downstream and upstream surfaces of the conducting target were measured in the geometry of the diffraction radiation. The surface currents were experimentally recorded on the upstream target surface, from which the backward diffraction radiation is generated. At the same time, the surface currents are absent on the downstream target surface, which is conventionally considered as a source of diffraction radiation in the direction of the motion of electrons. Analogous results were obtained in the same geometry in a beam of real photons. On the whole, these results confirm the applicability of the pseudophoton method for the analysis of the effects of the interaction between the field of relativistic photons and the thick (thicker than the skin layer) conducting targets and inapplicability of the surface current method for the radiation in the direction of motion of electrons.

Radiation properties of metamaterials in millimeter wavelength region

We propose and demonstrate a type of composite metamaterials, which is constructed by combining thin copper wires and split ring resonators on the same board. Using the optimized target parameters we had investigated the orientation-angular dependence of radiation refraction in metamaterial target. The measurements were performed in free space as well, as the spectral characteristics of refracted radiation in comparison with the initial spectra. The measured dependences show the formal correspondence of the radiation characteristics to the negative refraction index of the metamaterial structures. This correspondence is only formal one, which follows from the Snellius law, because really the permittivity and the permeability should be considered as macroscopic tensor characteristics of metamaterial.