Third-order optical nonlinearities of near-infrared dyes

Near-infrared dyes – di- and tri-indocarbocyanine dyes and nickel dithiolenes – were synthesized and their third-order optical nonlinearities in solutions were investigated by using the degenerate four-wave mixing technique. Large third-order nonlinear optical susceptibilities with γ values of up to 10−29 esu were observed. The γ value of the indocarbocyanine dyes increases with increase of conjugation length of the polymethine chain. The central ring structure in the chromophore lowers the γ value of the indocarbocyanine dyes. With change of the substituents on the benzene ring an increase in γ value is observed for all the asymmetric nickel dithiolenes. The order of increase of nonlinear hyperpolarizability is as follows: H<Cl<CH3<C2H5<CH(CH3)2.