Nonlinear optical responses of cyanine dyes in solution measured by resonant femtosecond degenerate four-wave mixing technique

摘要

Nonlinear optical responses of cyanine dyes in solution were studied by resonant femtosecond degenerate four-wave mixing (DFWM) technique. The folded box-CARS type geometry with the three linearly polarized beams of fundamental output of a regenerative amplified Ti:sapphire laser was used for the DFWM experiment. The wavelength of the laser was adjusted to the absorption band of the samples. Temporal profiles of a DFWM signal of cyanine dyes were measured with a time resolution of 0.3 ps, and were found to consist of three components, the coherent instantaneous nonlinear response (electronic response) and the medium and slow responses. The decay constant of ca. 100 ps can be attributed to the relaxation time of rotation around the short axis of the dye molecule. We think the decay constant of several ps can be attributed to the relaxation time of rotation around the long axis of the dye molecule. The effective value of the electronic component of the molecular hyperpolarizability, γ_e, was determined to be as large as 1.2 × 10~(-28) esu at 780 nm for NK-2014. The dependence of γ_e of NK-2014 on the laser wavelength was measured.