Spectral-polarization properties associated with the virtual state nature formed on two-photon fluorescence excitation of dye molecules

The spectral and polarization properties of fluorescence in dye solutions on two-photon excitation are studied. The conditions influencing a relative contribution of various mechanisms underlying the formation of a virtual intermediate state in the process of two-photon fluorescence excitation are determined. It is demonstrated that they are associated with the polarization and frequency characteristics of excitation fluxes and also with the electronic-vibrational molecular structure