Developments in Measuring Enhancement and Quenching of Optical Nonlinearities from Gold Nanoantennas

Entin, Nicholas

Undergraduate Honors Thesis

Developments in Measuring Enhancement and Quenching of Optical Nonlinearities from Gold Nanoantennas Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/undergraduate_honors_theses/rx913r50z

Abstract

Researchers have made incredible strides in exploring novel optical regimes involving the localization of electromagnetic fields to only a few nanometers and the corresponding dramatic enhancement of nonlinear optical effects. As scientists begin to unravel the mysteries of light-matter interactions on a nanoscale, many questions about nonlinear optical responses in metallic nanostructures remain unanswered. In Au nanostructures, the optical response from electronic transitions give rise to efficient nonlinear emissions, including the coherent four-wave mixing (FWM) and incoherent hot electron luminescence (HEL). Observations of spectral shift and near-field enhancement of nonlinear emissions have been observed for few nanometer distances, and deviations from the classical predictions are attributed to quantum effects. However, there is debate regarding the nanostructure coherent and incoherent light-matter interaction and how it is modified by quantum effects at small separations. Here, I will discuss the necessary background and foundational tools for experiments that will provide more insight on the emission mechanism for FWM and HEL in Au nanostructures. The fabrication process for Au nanoantennas in these experiments is described in detail, and modifications are made to improve the nanoantenna quality. For the first time, the experimental setup and measurement protocol are described, and we make significant progress in implementing a scanning tunneling microscope (STM) to the experiment. We demonstrate a functional STM system and make key design modifications that will allow the system to be used in future investigations. Finally, we show preliminary measurements and analysis methods that will contribute to understanding the coherent and incoherent near-field light-matter interaction at small interparticle separations. In addition to reviewing the motivational experiments and scientific analysis of successful measurements, these results serve as a valuable resource for future experiments by putting past protocols on paper and establishing foundational work to addressing the open science questions.

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