DETERMINATION OF THE 2-PHOTON ABSORPTION-SPECTRUM OF A SOLUBLE POLYTHIOPHENE

The two-photon absorption spectrum of the soluble conjugated polymer poly(3-octylthiophene) is measured in the visible range using the picosecond Kerr ellipsometry technique. The largest two-photon absorption feature peaks at 3.5 eV, which is 0.6 eV above the one-photon absorption peak. It has 0.27 eV half-width at half-maximum and 0.27 cm/GW magnitude in a 25 g/l solution. The average value of the associated transition dipole moment is 18 D. A weaker two-photon feature with 7 D average dipole moment which parallels the linear absorption spectrum is observed. it may be associated with some disorder-induced local non-centrosymmetry.