Third-order optical nonlinearities of poly(arylaminophenylenevinylene) studied with femtosecond pulses.

Time-resolved degenerate four-wave mixing (DFWM) experiments performed on films of triphenylamino-phenylene vinylene (TPA-PPV) copolymer show the modulus of the nonlinear refractive index to be (2.1 +/- 0.4) x 10(-13) cm(2)/W at 800 nm. The polymer was synthesized in the Hoerner-type polycondensation reaction. The films were characterized by optical absorption spectra, molecular weight and glass transition temperature measurements. The linear refractive index measurements performed with a prism coupler indicate that the annealed polymer films are isotropic. The films showed waveguiding of light. The DFWM experiments were performed in the forward BOXCARS geometry with simultaneous monitoring of the phase-matched and the non-phase-matched signals. This allowed measuring the nonlinearity of submicrometer thick films even in the presence of signals from a thick glass substrate. A cubic power dependence of the diffracted signal vs. pump intensity was observed as expected for the Kerr-type electronic nonlinearity. The signals showed a strong instantaneous response followed by a slow decay with the time constant 9 +/- 2 ps. Z-scan measurements showed the presence of two-photon absorption in the polymer.