Abstract

The Z-scan technique for measuring third-order optical nonlinearities has been proposed and demonstrated recently.¹ Using this technique, we measured the optically induced index change Δn for derivatives of imidazole-2-thione at a wavelength of 532 nm. In these materials, which are optically clear, we detected a quadratic relationship between the index change and the intensity in a 30–100-MW/cm² range, as opposed to the linear relationship we observed in absorptive materials. We also observed that the distance between peak and valley of the Z-scan data was less than predicted for third-order effect. This implies that the index change is a result of either the higher-order nonlinear effect or a combination of lower-order effects. Further investigation of the possible mechanisms and measurements in related compounds is discussed.

© 1991 Optical Society of America