• H.K. Avetissian, S.S. Israelyan, G.F. Mkrtchian, Kh.V. Sedrakian
  YSU, Yerevan

If in the spontaneous radiation processes of charged particles the medium with refractive index n>1 plays only a role of the third body, the presence of a medium at the interaction with external electromagnetic wave causes the new threshold phenomena which have an essentially nonlinear character. In the present work the case of strong laser field is considered within the scope of the relativistic quantum theory for electron-laser interaction in a medium. Using Strong Coupled State approximation the spectrum of eigenvalues of particle energy (in the rest frame of the wave) and the wave function is found. Due to the nonlinear resonant interaction with given laser field the equidistant levels of longitudinal motion are formed and as a consequence the spontaneous transitions from the upper levels take place with the emission of corresponding quanta. In the scope of Quantum Electrodynamics the spectral intensity of laser-assisted Cherenkov radiation is obtained. The first-order Feynman diagram is calculated where the electron lines correspond to the wave functions in the strong laser field and the resonant interaction is discussed.