NONLINEAR OPTICAL-RESPONSE OF ONE-DIMENSIONAL MOLECULAR-CRYSTALS - BREAKDOWN OF THE LOCAL FIELD APPROXIMATION

An analytical expression for the third order hyperpolarizability of an infinite one-dimensional molecular aggregate is derived, and compared with the same quantity calculated under the local field approximation. It is found that the peak nonlinear absorption is greatly overestimated in this approximation by a factor of (\J\/GAMMA)1/2, where J is the near neighbor dipole-dipole coupling and GAMMA is the molecular excited state lifetime.