Anomalies of polariton dispersion in photoexcited molecular crystals

Abstract

Green function and unitary transformation techniques are applied to study polariton formation in a molecular crystal placed in an intense external monochromatic light field. Using the exact tri-linear computation relations for Frenkel exciton operators, the energy of polaritons is shown to be dependent on exciton density. Then an effective Hamiltonian is constructed allowing one to obtain the light intensity-dependence of the exciton density. Due to possible bi-or multistability of the density, the calculated intensity-dependent polariton dispersion relations may exhibit different anomalies, such as the splitting of each polariton energy branch into two or several sub-branches and the appearance of supplementary intracrystal polariton-like waves even in the absence of exciton spatial dispersions.