Investigation of third-order nonlinearity of polybenzonitriles by heterodyned femtosecond optical Kerr gate

The femtosecond optical heterodyne detected optical Kerr effect is described in detail. The real and the imaginary parts of complex third-order optical nonlinearity can be effectively separated and their values and signs can be determined. Using this method, we thoroughly investigated the substitution effect by adding different side-groups on the -(-C=N-)- conjugated system, a new class of nonlinear optical material. We discussed the improvement in their third-order susceptibilities. And we found the value of second-order hyperpolarizability depends on the polymerization degree, but the relationship is different for different substituted polymers.