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Third order nonlinear optical effects in some polybenzidines
Abstract
Third order nonlinear optical properties of organic compounds with $\pi$ electron delocalization are currently receiving much attention in view of potential applications in switching and optical information processing. Polymers of Benzidine were synthesized by hydrogen peroxide reaction catalyzed by horseradish peroxidase enzyme. The polymerization reaction was carried out at room temperature in a monophasic organic solvent with a small amount of water at pH 7.5. The technique of Degenerate Four Wave Mixing with picosecond and nanosecond pulses was employed to measure the third order susceptibility $\chi\sp{(3)}$ of polybenzidine. The observed values for $\chi\sp{(3)}$ are of order 10$\sp{-9}$ to 10$\sp{-8}$ esu. In order to understand the origin of these high values of $\chi\sp{(3)}$, we measured the real and imaginary components of $\chi\sp{(3)}$. Investigation of total energy transmission as a function of incident intensity and fluence at 532 nm for picosecond and nanosecond laser pulses using a frequency doubled Nd:YAG laser indicates reverse saturable absorption. The experiments are carried out for the sample in solution in Dimethyl Sulfoxide and Methanol (DMSO:MeOH) 4:1 ratio. As we observe the nanosecond and picosecond curves to be superimposed for intensity dependence and not for fluence, we conclude that the third order nonlinearity is predominantly due to two photon absorption. Values for Im $\chi\sp{(3)}$ determined by our experiments are of order 10$\sp{-9}$ to 10$\sp{-8}$ esu. We measure the real part of $\chi\sp{(3)}$ by optical Kerr gate technique. The value is about one order lower compared to the imaginary component. In view of the reverse saturable absorption characteristics observed for the samples, the material is a good candidate for applications in optical power limiting.
Subject Area
Optics|Polymers
Recommended Citation
Cheng, Chi Fai, "Third order nonlinear optical effects in some polybenzidines" (1994). Doctoral Dissertations Available from Proquest. AAI9434467.
https://scholarworks.umass.edu/dissertations/AAI9434467