Center for Functional Nanomaterials Seminar

The nonlinear interaction between intense light and a dispersive medium is inherently frequency-dependent and can significantly vary across optical resonances in a material; therefore it is critical to examine the wavelength dependence of nonlinear parameters when characterizing new materials for nonlinear optical applications. To completely assess the working spectral ranges and nonlinear optical efficiencies of potential materials, a broadband excitation source must be available. I will show that all of the relevant nonlinear optical parameters (second- and third-order susceptibilities, multiphoton absorption coefficients, laser-induced damage thresholds, and phase-matching ranges) that should be considered for potential nonlinear optical applications can be probed with a nonlinear optical characterization technique involving wavelength and intensity dependence. The importance of this work relies on the fact that this technique is not limited to materials with specific physical morphologies, but can be used for any type of sample in question (i.e. monolayer, thin film, powder, or bulk crystal form). Specifically in this presentation, I will present my work on the characterization of nonlinear optical dispersions of novel oxide and chalcogenide semiconductors probed with a broadband picosecond excitation source. The basic theory of nonlinear optics will be described as well as the experimental apparatus for these measurements. A measurement of the two-photon absorption coefficient dispersion in tetrapod ZnO along with a broadband dispersion of the second-order susceptibility χ^((2) ) for Al-doped ZnO thin films will be presented. χ^((2) ) and χ^((3) ) were evaluated for promising infrared quaternary chalcogenides as well as laser-induced damage thresholds and Type-I phase-matching ranges. These nonlinear optical parameters are shown to be strongly correlated to the bandgaps of these chalcogenides. Finally, χ^((2) ) dispersions of monolayer transitio