Nonlinear optical properties of novel oxide/chalcogenide materials and structures.

摘要

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 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 thesis, I present my work on the characterization of nonlinear optical dispersions of novel oxide and chalcogenide semiconductors probed with a broadband picosecond excitation source. In Chapter 1, I describe the basic theory of nonlinear optics. In Chapter 2, the experimental apparatus for my measurement in described. In Chapter 3, I present a measurement of the two-photon absorption coefficient dispersion in tetrapod ZnO along with a broadband dispersion of the second-order nonlinear susceptibility chi(2) for Al-doped ZnO thin films. In Chapter 4, chi(2) and chi(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. In Chapter 5, chi(2) dispersions of monolayer transition metal dichalcogenides were obtained and found to be resonantly enhanced near the exciton states. For assessment in practical device applications, laser-induced damage thresholds were evaluated. Finally, the second-order nonlinear optical properties of MoS2 microcavities were measured.