Subpicosecond interferometric measurement of the nonlinear refractive index of poly(3-hexylthiophene)

We measured the magnitude and the time response of the nonlinear refractive index (n(2)) of poly(3-hexylthiophene)by a femtosecond time-resolved interferometric technique. Decays of 320 fs and 3.0 ps were found. The n(2) value obtained was -6 x 10(-9) esu at 620 nm. Calculation of the dispersion of n(2) showed that the negative value is consistent with that of a four-level model.