Excitons and polaritons in polymers

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Abstract
The coupling of the lowest excited electronic states of a long chain of molecules to the radiation field gives rise to collective excitations with some of the characteristics of polaritons in three dimensional solids. In the model considered, the polariton spectrum has two branches. The states of the first branch have lifetimes up to λ/a times shorter than the transition in the isolated molecule and are therefore superradiant. Resonances in the scattering amplitudes of incident plane wave monochromatic fields locate the energies of the first branch. The other branch is subradiant, i.e., it does not radiate at all, and has a linear dispersion relation over the greater part of the interval 0<ω≲ω1, where ω1 is the exciton transition frequency, and corresponds to a photon localized about the axis of the chain. The problem of detecting polaritons in long molecular chains is briefly discussed and the theory of polaritons in polymers on a transparent substrate is outlined.