The nonlinear optical response of interacting charge-transfer excitons with a weak probe in a strong pump field

The nonlinear optical response of interacting charge-transfer excitons is investigated theoretically by means of pseudospin operators for the model Hamiltonian. The generalized optical Bloch equations including the static dipolar interaction of charge-transfer excitons are derived in terms of the Heisenberg equation of motion and the mean-field approximation. It is shown that the intrinsic optical bistability due to the strong interaction of charge-transfer excitons may exist in the interacting charge-transfer exciton system. The absorption spectrum of interacting charge-transfer excitons associated with a weak probe field in the presence of a strong pump field is also calculated using the linear-response theory. The results show that a gain without population inversion can be observed in the interacting charge-transfer exciton system.