THE NONLINEAR OPTICAL PROPERTIES OF CLUSTERS (N-BU4N)4[MO8CU12O8S24] AND (N-BU4N)2[MOCU3OS3(NCS)3]

Abstract

The aim of this thesis is to determine the nonlinear optical properties of clusters (n-Bu4N)4[Mo8Cu12O8S24] and (n-Bu4N)2(MoCu3OS3(NCS)3] experimentally, and identify the responsible mechanisms. To measure the nonlinear optical properties of the two clusters, we established an automatic Z-Scan measurement system. We also developed a set of software to control data acquisition processes. With these hardware and software, we conducted open-aperture and closed-aperture Z-scan experiments at different wavelengths and incident irradiances to observe the nonlinear absorptive and refractive behavior of the clusters. We found that the two samples possess both nonlinear absorption and self-defocusing effects. We also monitored time-resolved nonlinear transmission to determine if the nonlinear absorption is an accumulated process, and whether the self-defocusing effect is an electronic or thermal process. The result of our experiments indicates that the nonlinear absorption is an accumulated process and the self-defocusing is an electronic process in nature. In the theoretical analysis, we assumed that energy structures of our samples are similar to that of Cao. We proposed a five-energy-level model to explain the nonlinear optical behavior of the samples. By comparing the model calculation with the experimental data, we found that the nonlinear absorption can be explained by excited triplet state absorption and the nonlinear refraction is caused by the saturation of an excited singlet state.