  Coherent transition radiation (CTR) from relativistic electron beam
interaction with an overdense plasma foil is investigated by making use of
two-dimensional particle-in-cell simulations. Well-defined single electron beam
either of uniform profile or having substructures is considered for various
beam-plasma parameters. The main purpose is to mimic the complicated
beam-plasma conditions that is often found, for example, in intense laser
plasma interactions. Key properties of the CTR concerning their temporal,
angular and spectral profiles are identified. Several saturation effects due to
the beam energy, size and foil density are found for the CTR energy, and the
dependences vary for different spectral components such as in the Terahertz
(THz) and optical range. The detailed substructure of the beam also affects
greatly the radiation generation, leading to distinctive high harmonic
components. Electrons with kinetic energy from sub MeV to tens of GeV are
explored. For few MeV electron beams, the effects of the foil plasma on the
beam dynamics and associated CTR generation, resembles closely the CTR from hot
electrons produced in intense laser-plasma interactions. These results may find
important applications in beam diagnostics either in laser-plasma based
acceleration or conventional accelerators. They may also be employed to design
novel THz radiation sources using tunable electron beams.
