Nonlinear optical properties of cyanine dye J-aggregates in thin films measured by Z-scan technique

The dispersion of cubic optical susceptibility of submicron films of cyanine dyes J-aggregates is measured by a z-scan technique. The values of Im(chi) (3), Re(chi) (3) near to J-peak were 10-5 esu. It was found that Im(chi) (3) has a negative sign but at a low-frequency side of J-peak the sign is reversed. The measured dependence of Re(chi) (3) ((omega) ) has compared with the value calculated by Kramers-Kronig transformation. The dispersion dependence of Im(chi) (3), Re(chi) (3) is quite well described on a basis of four-level model for J- aggregates.