Resonant third-order optical nonlinearities of 1,3-bis[(3,3-dimethylindolin-2-ylidene)methyl]croconine

The third-order optical nonlinearities and responses of a croconium dye (1,3-bis[(3,3-dimethylindolin-2-ylidene)methyl]croconine) in tetrahydrofuran (THF) solution and in poly(methyl methacrylate) (PMMA) coating films were measured using a femtosecond degenerate four-wave mixing (DFWM) technique with a time resolution of 0.3 ps (FWHM) system under resonant conditions. The electronic component of molecular hyperpolarizability, γe of the croconium dye in THF solution was determined to be about 5.3×10−29 esu at 773 nm. The electronic component of third-order nonlinear optical susceptibilities, χe(3) of the present PMMA coating films containing the croconium dye was measured to be of the order of 10−8 esu, and the figure of merit of third-order nonlinearity F  (F=χ(3)/α)(F=χ(3)/α), was evaluated to be about 8.3×10−14 esu cm. The χe(3) for a neat film was about 4.9×10−8 esu at 820 nm.