Terahertz radiation from an ultra-relativistic charge exiting the open end of a waveguide with a dielectric layer

Abstract

We analyze radiation produced by an ultrarelativistic charge as it exits the open end of a cylindrical waveguide with a dielectric lining. The end of the waveguide can be either orthogonal to the structure axis or skewed. To obtain terahertz radiation from waveguides with centimeter or millimeter radii, we consider high order TM(0m) modes driven by the beam. We obtain an integral representation which describes the radiation produced by a single waveguide mode in the Fraunhofer zone. We perform a series of numerical calculations for structures which look promising for generation of THz radiation. It is shown that for a mode with large mode number, the aperture of the vacuum channel gives the main contribution to the field if the skew angle of the waveguide aperture is not too small. Simple expressions for the angle of the main pattern lobe maximum are obtained.

Radiation of a charge moving along the boundary of dielectric prism

“…In previous papers, we have offered two methods for the solution of such problems which can be named "the ray-optics method" and "the aperture method" [6][7][8][9][10][11]. Both methods are valid for objects which are much larger than the wavelength under consideration, λ.…”

“…However, these conditions are often not met. Therefore, we have developed a more general "aperture method" which is valid for an observation point with arbitrary wave parameter D including a Fraunhofer (far-field) area (where D ≫ 1) and neighborhoods of focuses and caustics [8][9][10][11]. At the final step of this technique, we calculate the field outside the target using Stratton-Chu formulas ("aperture integrals").…”

Radiation of a bunch in a waveguide with a semibounded anisotropic dielectric

“…One of beam-based methods is using a metallic beam pipe with small corrugation [6,7]. DWA structures are also considered as promising candidates for generation of radiation in the Terahertz range [5,[8][9][10][11][12]. It is notable that direct experimental observation of wakefield effects in a THz regime was performed in a planar diamond accelerating structure [13] and in a cylindrical dielectric-lined waveguides with the use of tubes fabricated from fused silica [14] and chemical-vapor deposition diamond [15].…”

Radiation of a charge exiting open-ended waveguide with dielectric filling

“…Nevertheless, rigorous solution for the electromagnetic (EM) field produced by a charged particle bunch passing from the open-ended circular waveguide with dielectric filling is still missing even in the case of orthogonal end cut. In particular, such a solution is required for determination of the area of applicability of the approximate technique used in [7] and it's possible improvement.…”