Two-photon fluorescence spectrum in an atom plus dielectric microsphere system

A strong resonant interaction of a two-level atom with a dielectric microsp here is studied on the basis of quantum electrodynamics. The initial condit ion considered is one in which the atom is initially excited and the resona nt mode of the microsphere has been excited by a single photon. The spectru m of two emitted photons depends strongly on the method used to excite the microsphere, i.e., on the spatial distribution of the photon energy. The mo st characteristic feature of the two-photon fluorescence spectrum is a stro ng energy correlation of the emitted photons. This correlation is expressed in the fact that the energies of the emitted photons are related by the eq uation of an ellipse (omega(1)+omega(2)-2 omega(A))(2)+3(omega(1)-omega(2)) (2)=4 Omega(Rabi)(2). The relation between the results obtained and the pre dictions of the theory of dressed states is discussed. (C) 1999 American In stitute of Physics. [S0021- 3640(99)00715-X].