Since Ebbesen's seminal work in 1998 observing extraordinary optical transmission (EOT) through nanohole arrays, much research has focused on the role of surface plasmon polaritons (SPPs) in EOT. While the energy and momentum conditions have become clear, no consensus has been reached on the role of incident light polarization. This study presents a simple model that captures Bloch-SPP excitation, including the role of polarization, in general periodic plasmonic structures. Our model predicts that under certain conditions polarization conversion should occur in EOT light transmitted through the nanohole array. We experimentally measure polarization conversion in EOT and compare the experimentally obtained results to the predictions of our model. Using numerical simulations, we tie the far field experimental results to the near field underlying physics described by our model. In using polarization conversion to provide evidence supporting our model, we also establish a novel approach to achieving polarization conversion based on SPPs instead of hole shape or other techniques in literature, and present reasons why this approach to achieving polarization conversion may be better suited for applications in biomedical sensing and optical elements. / Master of Science / In 1998, Ebbesen et al¹ observed that when light is shown on a metal nanofilm perforated with nanoholes more light appears on the other side of the metal film than was incident on the nanoholes. The unexpectedly high transmission of light through the nanohole array was termed extraordinary optical transmission (EOT), and quickly found applications in diverse fields such as biomedical sensing<sup>13,14</sup>, energy harvesting<sup>12,31</sup>, and nonlinear optics<sup>12–14,24</sup> . As the importance of EOT in applications became clear, interest developed in understanding the fundamental physics involved. Over the next 20 years, researchers showed that the incident light (made up of electromagnetic fields) excites conduction electrons on the surface of the metal film¹¹ . Specifically, the light and the electrons couple to form quasiparticles known as surface plasmon polaritons (SPP) which propagate along the surfaces of the metal film. The SPPs on the back surface of the metal film then radiate free space transmitted light, which is observed as EOT. However, much of the physics involved how SPPs mediate EOT has remained unclear.
The first focus of this work is theoretical, presenting a microscopic model for SPP mediated EOT. In contrast to many groups which aim to characterize SPPs from their far field properties, our model focuses on the near field microscopic physics and presents the far field properties as a consequence of the near field physics. Since the near field cannot be probed iv experimentally, we use numerical simulations to both verify our model’s predictions in the near field and predict the properties that should be measured in the far field.
The second focus of this work is more applications driven. We notice that our model predicts that under certain conditions SPPs should cause a phenomenon known as polarization conversion to occur, which is when the polarization of the transmitted light is different from the polarization of the incident light. We experimentally measure the predicted polarization conversion, thereby providing substantial experimental evidence in support of our theoretical model. Our novel approach to achieving polarization conversion based on the behavior of SPPs differs substantially from the approaches in literature (usually based on hole shape²⁴). We present the reasons why our SPP-based approach to achieving polarization conversion is more robust to fabrication imperfections than the conventional approaches, and describe how our approach could affect various applications.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/83408 |
| Date | 29 May 2018 |
| Creators | Debroux, Romain L. |
| Contributors | Electrical Engineering, Zhou, Wei, Poon, Ting-Chung, Economou, Sophia E. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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