Wavelength dependence of the third-order nonlinear optical properties of apolythiophene/selenophene derivative film

The third-order nonlinear optical properties of a hybrid polymer film conta ining substituted thiophene rings copolymerized with unsubstituted selenoph ene were measured using the Z-scan technique. Large, resonantly enhanced th ird-order nonlinearities were found at wavelengths on the low-energy side o f the absorption band. In contrast to the results on a similar copolymer fi lm incorporating only thiophene, a strong two-photon absorption appeared in the near infrared. The imaginary part of the third-order susceptibility ca n be adequately explained as saturation of an exciton band, while the origi n of the large negative real part is unknown. (C) 1999 American Institute o f Physics. [S0003-6951(99)04947-5].