Nonlinear optical effects occur when strong electromagnetic waves induce changes in a medium that affect its own propagation or that of another wave. Third order optical nonlinearities scale linearly with irradiance and lead to effects like two-photon absorption and nonlinear refraction. This work focuses on the experimental and theoretical study of two-photon absorption in crystalline solids. We begin by detailing the quantum mechanical states of electrons in solids along with the computational approaches to calculate their band structure. Next, a theoretical model for the linear and nonlinear optical interaction of light with matter is presented in a many-body formalism. This first-principles approach derives first and third order nonlinear optical coefficients directly from the many-body Schrödinger equation coupled to the electromagnetic wave equation through the current densities excited by incident electromagnetic fields. The following work examines nondegenerate two-photon absorption in semiconductor quantum well waveguides to determine their suitability as a two-photon lasing medium under population inversion. Experimental pump-probe measurements are presented for a structure comprising GaAs/32% AlGaAs quantum wells. The data is first analyzed by devising a theoretical model for the co-propagation of a strong pump and weak probe pulse within the wave guide sample. After, we present a quantum mechanical model for the electronic states and corresponding optical response of our system to compare to the two-photon absorption coefficients determined from the experimental investigation. The model's excellent agreement with the measured results allows us to extrapolate to the extremely nondegenerate regime, predicting large enhancements in the nondegenerate two-photon absorption coefficients when one pulse has a mid-infrared wavelength. Next, we detail phonon-assisted nondegenerate two-photon absorption in silicon, with the goal of determining which transition pathway best explains the dispersion of ND-2PA coefficients near the band gap energy. After discovering many cases where simplified models break down, we introduce a tool to calculate linear and nonlinear optical properties of materials using density functional theory. This work focuses on the efficient calculation of one- and two-photon absorption, as well as the nonlinear effects arising from excited carrier populations. Finally, a theoretical model is proposed to determine the exact many-body quantum states of materials including electron-electron Coulomb interactions.
| Identifer | oai:union.ndltd.org:ucf.edu/oai:stars.library.ucf.edu:etd2020-2367 |
| Date | 01 January 2022 |
| Creators | Cox, Nicholas |
| Publisher | STARS |
| Source Sets | University of Central Florida |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Electronic Theses and Dissertations, 2020- |
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