Degree Name

Department

Chemistry and Biochemistry

College

Physical and Mathematical Sciences

Defense Date

2018-11-07

Publication Date

2018-12-07

First Faculty Advisor

James E. Patterson

First Faculty Reader

David T. Fullwood

Honors Coordinator

Merritt B. Andrus

Keywords

spectroscopy, materials, aluminum, silicon, sum frequency generation, second harmonic generation, nonlinear optics, beta phase aluminum

Abstract

Vibrational Sum Frequency Generation (VSFG) and the similar Second Harmonic Generation (SHG) are both classified as nonlinear optical phenomena, with the hallmark trait being that the input and output frequencies are different. Both of these systems are remarkable tools due to their surface specific nature. Still, there is much that is not known about the response from these systems, especially the nonresonant SFG response. We have worked to better understand SFG signal, specifically the nonresonant temporal profile. We have also collected results that call into question some underlying assumptions about time-based suppression methods when working with single crystal substrates.

As an extension of this work we have also investigated the limits of SHG as a possible method for stress testing. Nondestructive testing (NDT) is the assessment of a component to determine its viability of use without damaging the component itself. Early results have shown that SHG has the capability to be used as an NDT platform. SHG sensitivity to surface and interface changes has been shown in mechanical deformation in aerospace grade aluminum, and in chemical changes in naval grade aluminum. SHG signals from a metal surface change as the chemical or physical makeup of the surface changes. Results show that SHG has the potential to be dramatically more sensitive than current methods and allows us to identify the earliest stages of material response to mechanical and chemical stress.

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