New two−photon absorption spectrometer and its application to diphenylbutadiene

We describe a new spectrometer which promises to increase by several orders of magnitude the sensitivity for measurement of aboslute two−photon absorptivities. The spectrometer employs two TEM00 laser beams propagating in opposite directions through the sample. A tunable pulsed laser generates the powerful beam and a continuous krypton ion laser provides a constant frequency probe beam for the two−photon spectrometer. We report the two−photon absorptivity of 1−chloronaphthalene at 35 400 cm−1 to be 1.3×10−50 cm4 sec photon−1 molecule−1, in good agreement with previously reported values. We also report the two−photon absorptivity of 1,4−diphenyl−1,3−butadiene at 28 259 cm−1 to be 1.0×10−50 cm4 sec photon−1 molecule−1. This relatively high value indicates the presence of a previously undetected 1Ag excited state as the lowest excited singlet state of this molecule.