Applied and extended modeling of optical interference effects towards sum frequency generation in multilayer thin films

Abstract

Sum frequency generation is a powerful technique to elucidate the molecular order and orientation of interfacial molecules where a bulk media typically prevents characterization. Additionally, optical interference effects further complicate analysis of the sum frequency response as constructive and destructive interference alter the intensity of the measured signal. Quantitative assignment of the interfacial molecules requires an accounting of the optical properties of the films to solve the present interference. Performance of this analysis requires a modeling routine. Current routines struggle with performance issues including slow functionality and a lack of user friendliness. Within this work, construction of a novel fitting routine is documented. The routine uses transfer matrix formalism to describe the optical propagation of light throughout the relevant thin film systems. It is applied to resolve interfacial questions for prototypical electronic materials. In the first chapter, the modeling is used to determine the packing of interfacial molecules as the thickness of the vibrationally active material is varied. In the second, I studied a system with a temperature-dependent packing structure. Following, the model is extended to explore the refractive indices: both their value and treatment. In Chapter 4, I offer a novel perspective by leveraging the optical inferences in a sum frequency generation experiment to solve the refractive indices, as the descriptive transfer matrix formalism is highly dependent on the complex terms. Finally, the description of the material boundary is explored, ranging from distinct to continuous, and the effects on the sum frequency signal are demonstrated in Chapter 5.