Resonant enhancement of third-order nonlinear optical property in J-like aggregates of a cyanine dye

The wavelength dependence of the third‐order optical nonlinearity and response of the J‐like aggregates of a cyanine dye called NK‐3261 in a neat film were measured by the femtosecond degenerate four‐wave mixing (DFWM) technique under resonant conditions. The temporal profile of the DFWM signal of NK‐3261 J‐like aggregates was found to consist of three components, i.e., coherent instantaneous nonlinear response (electronic response) and the two slow responses with decay time constants of ca. 0.9 ps and ca. 5.6 ps. The electronic component of the effective third‐order nonlinear optical susceptibility, χ(3)e, of NK‐3261 J‐like aggregates was as high as ca. 5 × 10−7 esu at 850 nm. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)