Stimulated excitation of resonant Cherenkov radiation at a large number   of neighbouring waveguide modes
  The resonance Cherenkov radiation generated from a train of equally-spaced unidimensional electron bunches travelling along the axis of a hollow channel inside an infinite cylindrical waveguide filled with (weakly dispersing) transparent dielectric has been investigated. It was shown that its excitation might be stimulated at a large number of neighboring modes of the waveguide. A visual explanation of this effect is given and the possibility of its observation in the range of terahertz radiation is discussed. 
L.Sh. Grigoryan, S. R. Arzumanyan, H. F. Khachatryan, M. L. Grigoryan
physics.acc-ph cond-mat.other