High order nonlinearities and many photon effects in the exciton spectrum region of organic based crystals

The nonlinear effects of organic based crystals in which the Frenkel type of excitons are realised were studied. It is shown by using of the nonequilibrium Green function method that significant nonlinearities can arise in such type of crystals at moderate pump intensities owing to interaction of excitons. Effective parameter responsible for nonlinear effects is "gNp", where g is the constant of exciton-exciton interaction and N_p is the free photon density. The great crystal nonlinearities together with natural (nonlinear) boundary condition give rise to multistability effects in transmission and reflection light. The switching devices similar to optical key can be realised on this base.