Characterization Of Nonlinear Absorption And Refraction In Advanced Materials

We discuss the characterization of nonlinear optical processes in materials associated with loss and index changes using the Z-scan. The primary problem addresses is, given a new material, how do you determine the dominant nonlinearities present and their physical mechanisms. In particular, in extensive studies of a wide variety of materials we have found that there is seldom a single nonlinear process occurring. Often several processes occur simultaneously sometimes in unison, sometimes competing. Distinguishing and separating these processes is important for understanding and modeling the interaction. There are a variety of methods and techniques for determining the nonlinear optical response, each with its own weaknesses and advantages. In general it is advisable to use as many complementary techniques as possible and vary as many experimental parameters as possible in order to unambiguously determine the active nonlinearities. Here we show as examples the two cases of semiconductors and reverse saturable absorbing dyes. We concentrate on the use of the Z-scan in determining the responses, but utilize knowledge from other experiments to help in the interpretation