We investigated the third-order nonlinear optical properties of several soluble π-conjugated polymers with a goal of reliable determination of the parameters that characterize the nonlinearity, such as the real and imaginary parts of the nonlinear refractive index <i>n</i><sub>2</sub> and the one-photon loss and two-photon loss merit factors <i>W</i> and <i>T</i>, respectively. The measurements were performed at 800 nm with 100-fs pulses from an amplified Ti:sapphire system. We present results of investigations of several 2, 5-substituted poly(<i>p</i>-phenylene vinylenes), including poly[2-methoxy-5-(2′-ethyl-hexyloxy)-<i>p</i>-phenylenevinylene] and a soluble ladder poly (<i>p</i>-phenylene) polymer. In particular, Z-scan measurements of polymer solutions were found to be useful for the determination of the complex nonlinear refractive index. The results could be verified by time-dependent degenerate four-wave mixing studies performed on thin films of the polymers. We found generally good agreement between the values of <i>n</i><sub>2</sub> determined from Z scan and those from degenerate four-wave mixing. The results indicate that the nonlinear refractive index of the order of 10<sup>−12</sup> cm<sup>2</sup>/W can be readily obtained for various conjugated polymers. However, the two-photon merit factors <i>T</i> larger than unity are commonly encountered within the two-photon absorption ranges of these compounds.
© 1998 Optical Society of America
(160.4330) Materials : Nonlinear optical materials
(160.5470) Materials : Polymers
(190.4380) Nonlinear optics : Nonlinear optics, four-wave mixing
(190.4710) Nonlinear optics : Optical nonlinearities in organic materials
Marek Samoc, Anna Samoc, Barry Luther-Davies, Zhenan Bao, Luping Yu, Bing Hsieh, and Ullrich Scherf, "Femtosecond Z-scan and degenerate four-wave mixing measurements of real and imaginary parts of the third-order nonlinearity of soluble conjugated polymers," J. Opt. Soc. Am. B 15, 817-825 (1998)