COOPERATIVE ULTRAFAST NONLINEAR-OPTICAL RESPONSE OF MOLECULAR NANOSTRUCTURES

The stationary nonlinear reflection and the time resolved four wave mi xing signal from a molecular monolayer are calculated using Green func tion techniques. Cooperative resonant nonlinear response found in smal l aggregates suggests the existence of coherence size of order of opti cal wavelength. A new peak in the nonlinear reflection spectrum is pre dicted, which is missed by the local field approximation. For an infin ite two dimensional molecular monolayer with transition dipole moments in the lattice plane, the momentum-dependent two exciton decay rate i s found to be larger than the sum of the single exciton radiative deca y rates, as predicted by the local field approximation.