Forward transition radiation in a medium with excited atoms

On the basis of the quantum theory of radiation, we study the characteristics of forward transition radiation not predicted by the semiclassical radiation theory (which uses a nonquantized electromagnetic field) and not described by the index of refraction of the medium.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 57–61, February,1986.The author thanks the participants of a seminar conducted by V. L. Bonch-Bruevich for useful discussions.