The third-order optical nonlinearities of carbon nanotube modified conjugated polymer in the femtosecond and nanosecond regimes

Multiwalled carbon nanotubes (MWCNTs) have been noncovalently modified with poly[2-methoxy 5-octyoxy]- p -phenylene vinylene (MO-PPV) to form a series of solution of MWCNTs and the conjugated polymers. The third-order nonlinearities of the solutions were investigated by the optical Kerr effect technique with femtosecond pulses, and degenerate four-wave mixing, open aperture, and closed aperture Z -scan techniques with nanosecond pulses. We attempted to quantify the contributions from various channels including the real and imaginary parts, the dynamic carriers, two-photon absorption, and thermal effect. The MO-PPV/MWCNTs composites showed much larger third-order nonlinearities than the pristine polymers. The enhanced optical nonlinearities were attributed to the strong interaction between the π -π electrons of MO-PPV and MWCNTs in their photoexcited state.