Excited-state nonlinearity in polythiophene thin films investigated by the Z-scan technique

Measurements of the third-order optical nonlinear susceptibility χ(3) have shown that nonlinearity around the single-photon absorption region is dominated by the saturation absorption in polythiophene thin films. The sign and the size of the real and the imaginary part of χ(3) have been measured at 532 nm to be −6.1 × 10−9 and −1.9 × 10−9 esu, respectively, by the Z-scan method.