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, γe, was determined to be as large as 1.2
× 10-28 esu at 780 nm for NK-2014. The dependence of γe of NK-2014 on the laser wavelength was measured.
Nonlinear optical properties of perylene derivatives were studied by femtosecond Z-scan technique. 3,4,9,10-Perylenetetracarboxylic dianhydride (PTCDA), 3,4,9,10-perylenetetracarboxylic diimide (PTCDI), and perylene-66
(dibenzthiophenoperylene-N,N'-dicyclohexylimide), were studied. Tetrahydrofuran was used as a solvent for perylene-
66. The solubility of PTCDA and PTCDI is very poor. Their colloidal solution was prepared by the irradiation of the
third harmonics of a pulsed YAG laser to opaque suspension of PTCDA and PTCDI. Transparent colloidal solution was
obtained within 50 minutes of UV irradiation. Colloidal solution of quinacridone was also studied. Two-photon
absorption cross sections of these dyes were measured by open aperture Z-scan method using a femtosecond laser. The
dependence of two-photon cross section on laser wavelength was measured in the wavelength range of 780-820 nm.
The third-order optical nonlinearities and responses of sol-gel silica coating films containing J-like aggregates of a cyanine dye, NK-1967, were measured by the femtosecond degenerate four-wave mixing (DFWM) technique under resonant conditions. While NK-1967 in aqueous solution showed an absorption maximum at 742 nm, J-like aggregates of NK-1967 in sol-gel silica coating films showed that at 877 nm. Though the sol-gel silica coating films were stable at room temperature, they began to decompose after 10 minute irradiation at a laser power of 5 GW / cm2. The temporal profiles of the DFWM signal were measured with a time resolution of 0.3 ps, and were found to be almost same as that of CCl4, i.e., the coherent instantaneous nonlinear response was dominant. The contribution of slow response with decay time constants of ca. 1 ps was very small. The electronic component of the effective third-order optical nonlinear susceptibility of one of the films had a value of ca. 2.0 x 10-8 esu at 850 nm. The present value for the sol-gel silica coating film containing the J-like aggregates of NK-1967 is four orders of magnitude greater than that of CS2.
The third-order optical nonlinearities and responses of thin films containing the J-aggregates of a cyanine dye or a squarylium dye were measured using the degenerate four-wave mixing (DFWM) technique under resonant conditions. The sol-gel silica coating films containing the J-aggregates of the cyanine dye, NK-3261, are stable at room temperature and durable against laser beam irradiation. The temporal profiles of the DFWM signal were measured with a time resolution of 0.3 ps, and were found to consist of at least three components, i.e., the coherent instantaneous nonlinear response and the two slow responses with delay time constants of ca. 1.0 ps and ca. 5.6 ps. The contribution of the later was small. The electronic component of the effective third-order optical nonlinear susceptibility of the film had value of as high as ca. 3.0 x 10-7 esu. We also studied the neat film of a squarylium dye J-aggregates. The temporal profile of the DFWM signal of the neat film of squarylium dye was also found to consist of at least three components, the coherent instantaneous nonlinear response and the delayed response with decay time constants of ca. 0.6 ps and ca. 6.5 ps. The contribution of the slow tail was also very small. The electronic component of effective third-order optical nonlinear susceptibility of the neat film of squarylium dye had value of as high as ca. 3.6 x 10-8 esu.
We present the experimental results on the third-order nonlinearities of several porphyrin and naphthalocyanine derivatives measured by the femtosecond degenerate four-wave mixing (DFWM) technique under resonant conditions. Studies in the solvent effect on the third-order optical nonlinearities indicate that molecular packing in the solutions has significant effects both on the magnitude of the third-order nonlinear optical susceptibility, χ(3), and the DFWM response. The electronic component of the molecular hyperpolarizability, γe, was evaluated to be in the range of 0.9 x 10-29 esu to 2.3 x 10-29 esu for these compounds, where the zinc complex of the porphyrin derivative (ZnTTMAPP) showed the largest γe. These values are two orders of magnitude larger than the reported values measured under non-resonant conditions. The time-resolved results indicate that the relaxation of the excited state population dominates the DFWM response in these macrocycles.
Third-order optical nonlinearities of sol-gel silica coating films containing metal porphyrin derivatives were measured under resonant conditions by the femtosecond degenerate four-wave mixing (DFWM) technique. Temporal profiles of the DFWM signal were measured with a time resolution of 0.3 ps, and were found to consist of two components, the coherent instantaneous nonlinear response and the delayed response with a decay time constant of several to several hundred ps. The latter can be attributed to population grating of an excited state, and contribution of slow component was very little for a zinc porphyrin derivative. The values of electronic component of the optical nonlinear susceptibility, χ(3)xxxx, for these films were ca. 2 x 10-10 esu.
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, Iχ(3)eI, of one of the present films was as high as ca. 1.3 × 10-8 esu (1.8 × 10-16 m2 V-2 in SI) at 760 nm.
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