Ultrafast properties of plasmonic nanorod metamaterial

Student thesis: Doctoral ThesisDoctor of Philosophy

Abstract

Plasmonic metamaterials have customized linear and nonlinear optical properties. This thesis investigates the properties of an anisotropic plasmonic metamaterial, consisting of aligned, interacting gold nanorods, to perform ultrafast light modulation, exploiting the intrinsic Kerr nonlinearity of gold. This e ect is based on an illumination-intensity-dependent change in the gold's permittivity, which takes place on ultrafast timescales and induces the intensity-dependent change of the metamaterial's re ection and transmission. A comprehensive theoretical and numerical analysis of the linear and nonlinear response of various con gurations of the metamaterial is performed and compared to experimental results. A new family of hyperbolic waveguided modes above the e ective plasma frequency, enabled by spatial dispersion, is identi ed. The strong nonlinear response and the dynamic modulation capabilities associated with the excitation of the waveguided modes is investigated. The presence of strong electron temperature gradients in the nanorods induced by a control light is shown to determine a stronger nonlinear modulation and to in uence the dynamic response, leading to subpicosecond time recovery components of the nonlinearity. Weak and strong coupling between molecular excitons and the metamaterial's modes can be achieved using core-shell nanorod geometries. The coherent interaction of molecular J-aggregates with coreshell nanorod arrays is analyzed in both the weak and strong coupling regimes. Subpicosecond components of the modulation are determined in the strong coupling conditions. The design of the optical response of the gold nanorod and core-shell metamaterials is studied through the near- to mid- Infrared, key spectral regions for molecular ngerprinting in chemical sensing and absorption spectroscopy. The applicability limits of the analytic approaches using the quasi-static and e ective medium approximations is tested. The results show great potential of the plasmonic nanorod metamaterial for ultrafast nonlinear optics in free-space and integrated applications, in a broad spectral range.
Date of Award2016
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorAnatoly Zayats (Supervisor) & Gregory Wurtz (Supervisor)

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