Nonlinear optical properties of soluble substituted polysilanes and polygermanes

Abstract

The third order susceptibilities of a number of polysilanes and polygermanes for frequency tripling have been measured by Maker fringe techniques on thin polymer films coated on quartz substrates. This technique allows the measurement of the χ(3) value for the polymer relative to the known value of quartz by determining the intensity of the corresponding third harmonic signal generated as a function of the angle of incidence of the polarized laser light on the sample. The desired fringes were created by the rotation of the sample around an axis which was parallel to the polarization of the fundamental beam. The values are quite large for a sigma bonded system as predicted by the highly polarizable nature of the polymer backbone and the intense σ-σ* electronic transition in the ultraviolet. In many cases, the numbers are as large as those measured for polymers containing conjugated pi systems.