Nonlinear resonance reflection from and transmission through a dense glassy system built up of oriented linear Frenkel chains: Two-level model

A theoretical study of the resonance optical response of assemblies of oriented short (as compared to an optical wavelength) linear Frenkel chains is carried out. Despite the fact that the energy spectrum of a single chain is composed of the bands of Frenkel exciton states, a two-level model is used to describe the optical response of a single linear chain. We account for only the (on-resonance) optical transition between the ground state and the state of the one-exciton band bottom as having the dominating oscillator strength as compared to the other states of the one-exciton manifold. The (off-resonance) process of creation of two excitons per chain is neglected because it requires a higher excitation frequency due to the quasi-fermionic nature of one-dimensional Frenkel excitons. A distribution of linear chains over length resulting in fluctuations of all exciton optical parameters, such as the transition frequency and dipole moment as well as the radiative rate, are