Nonlinear Optical Properties of Ladder Polymers and Their Model Compound

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Abstract
The third order nonlinear optical properties of thin films of polybenzimidazobenzophenanthroline ladder (BBL) and semi–ladder (BBB) polymers and their model compound cis–BBB were investigated by picosecond, third harmonic generation. The χ(3) (−3ω, ω ω, ω) spectrum of BBL, BBB, and cis-BBB was obtained in the wavelength range 1.0–2.4µm and shown to exhibit a three–photon peak at respectively 1.695, 1.695, and 1.50 µm. The magnitude of the three–photon enhanced χ(3) was 6.40×10−11, 3.15×10−11, and 0.77×10−11 esu, respectively, for BBL, BBB, and cis–BBB. The results show that the χ(3) of BBL and BBB is enhanced by a factor of 50 and 17, respectively, relative to the model compound cis–BBB at 1.05µm.