Two-photon absorption spectrum of 3-butoxycarbonylmethylurethane polydiacetylene thin films

We report the two-photon absorption (TPA) spectrum of a film of poly[4,6-dacadiyne-1,10-diolbis(3-butoxycarbonyl-methyl-urethae)] -commonly known as poly(3-BCMU)-in the wavelength range lambda=1.6-0.7 mu m. We find that the TPA coefficient of the film, which was prepared by spin coating, increases from approximate to 2 cm/GW at 1.45 mu m to 170 cm/GW at 0.8 mu m. The main features of the spectrum can be accounted for by a three-level model with a two-photon state positioned at 2.8 eV. (C) 1998 American Institute of Physics. [S0021-9606(98)51110-5].