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-urethane)]—commonly known as poly(3-BCMU)—in the wavelength range lambda = 1.6–0.7 µm. We find that the TPA coefficient of the film, which was prepared by spin coating, increases from [approximate] 2 cm/GW at 1.45 µm to 170 cm/GW at 0.8 µm. 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