Loss of coherence of exciton polaritons in inhomogeneous organic microcavities

The question about the excitation spectrum in a microcavity containing a disordered organic film as a material with electronic transition is examined using a microscopic approach. It was argued previously that "conventional" polaritonic states (i.e., the states, which can be characterized by a wave vector) appear only for some intervals of the wave vector restricted by so-called end points. In this paper this is proved on the basis of a microscopic model. We consider two inhomogeneities, which lead to the nonconservation of the wave vector of polaritons: (i) structural disorder and (ii) energy broadening of the electronic transition. It is shown that investigating the influence of the inhomogeneity of the medium on cavity polaritons one should distinguish between a perturbative scattering by the fluctuations in the medium and a resonant scattering originating from the energy broadening of the electronic transition. It is discussed which mechanism is responsible for the appearance of each of the end points.