Large third-order optical nonlinearity and very fast response of cyanine dye doped thin films measured by resonant femtosecond DFWM technique

The third-order optical nonlinearity and response of polyvinyl alcohol coating films containing a cyanine dye called NK-2612 or NK-3261, were measured by the femtosecond degenerate four-wave mixing (DFWM) technique under resonant conditions. Temporal profiles of the DFWM signal were measured with a time resolution of 0.3 ps, and were found to consist of at least two components, the coherent instantaneous nonlinear response and the delayed response. It was demonstrated that the latter can be adjusted by the concentration of dye in thin films, and very fast nonlinear optical response was observed at high dye concentration. The electronic component of the effective optical nonlinear susceptibility, Ichi(e)((3))I, of one of the present films was as high as ca. 1.3 X 10(-8) esu (1.8 X 10(-16) m(2) V-2 in SI) at 760 nm.