Surface Plasmon Polaritons at Terahertz Frequencies on Metal and Semiconductor Surfaces

Table of Contents

1 Introduction

1.1 Electromagnetic interface excitations

1.2 Surface plasmon polariton

1.3 Terahertz frequency range

1.4 Conceptual formulation of this thesis

2 Theory of Surface Plasmon Polaritons

2.1 Classical field equations

2.2 Surface plasmon polaritons at a single interface system

2.3 Surface plasmon polaritons at a two interface system

2.4 The Drude model

2.4.1 A classical model for metals

2.4.2 Modified Drude model for doped semiconductors

2.4.3 Optical properties of investigated materials

2.4.4 Limitations of the Drude model

2.5 Numerical results for single and two interface systems

2.5.1 SPPs at gold and semiconductor surfaces

2.5.2 SPPs at dielectric covered gold surfaces

2.6 Coupling between free electromagnetic waves and surface plasmon polaritons

2.6.1 Aperture coupling

2.6.2 Prism coupling

2.6.3 Grating coupling

3 Experimental Setup

3.1 Terahertz time-domain SPP spectroscopy

3.2 Sample fabrication

4 Experimental Results

4.1 Coupling of Free Electromagnetic Radiation to Surface Plasmon Polaritons

4.1.1 Aperture coupling

4.1.2 Prism coupling

4.2 Study of dielectric coated gold surfaces

4.3 Study of semiconductor surfaces

4.3.1 SPP decay perpendicular to the semiconductor surface into air

4.3.2 SPP damping along the propagation direction

Research Objectives and Scope

This thesis provides the first experimental investigation into the propagation characteristics and spatial field distribution of surface plasmon polaritons (SPPs) within the terahertz (THz) frequency range. The primary research objective is to demonstrate the generation and systematic analysis of SPPs at flat surfaces of diverse materials, including metallic and semiconducting structures, to establish a foundational understanding of their behavior in the THz spectral gap.

• Design and implementation of a THz time-domain spectroscopy setup tailored for SPP investigation.
• Theoretical modeling of SPPs using the Drude model for various materials and interfaces.
• Experimental evaluation of aperture coupling efficiency for broadband THz radiation into SPP modes.
• Analysis of SPP confinement and decay properties at gold surfaces and dielectric-coated interfaces.
• Investigation of semiconductor surfaces (doped Si and InSb) for tunable SPP field characteristics.

Excerpt from the Book

Summary of Chapters

1 Introduction: Provides a qualitative overview of interface excitations, introduces surface plasmon polaritons, discusses the THz frequency range, and outlines the thesis structure.

2 Theory of Surface Plasmon Polaritons: Establishes the theoretical framework using classical electrodynamics, the Drude model, and boundary conditions to describe SPP behavior on single and two-interface systems.

3 Experimental Setup: Details the design and implementation of the THz time-domain SPP spectroscopy system, including the generation of pulses and the fabrication of material samples.

4 Experimental Results: Presents measurements of SPP coupling efficiencies, decay lengths at dielectric-coated gold interfaces, and investigates semiconductor surfaces with tunable carrier concentrations.

Keywords

Surface Plasmon Polaritons, THz time-domain spectroscopy, Drude model, electromagnetic interface excitations, terahertz frequency range, aperture coupling, semiconductor surfaces, dielectric coating, charge carrier concentration, field confinement, plasmonic revolution, optical constants, thin film analysis, electromagnetic field distribution.

Frequently Asked Questions

What is the core focus of this research?

The work focuses on the experimental study of surface plasmon polaritons (SPPs) in the terahertz frequency range, investigating their propagation and field distribution on various material surfaces.

What are the primary thematic areas explored?

Key themes include theoretical electromagnetics of interface modes, experimental THz spectroscopy techniques, the influence of dielectric thin films on SPP confinement, and the manipulation of SPP properties in semiconductors via doping.

What is the main objective of the thesis?

The primary goal is to conduct a fundamental investigation into THz SPPs, establishing how they can be efficiently generated and characterizing their behavior through systematic experimental measurements.

Which scientific methods are utilized?

The research utilizes THz time-domain spectroscopy (THz-TDS) and applies the Drude model for calculating permittivities and predicting field behavior.

What topics are covered in the main body?

The main body covers the theoretical foundation of Maxwell's equations and Drude theory, the development of a specific measurement setup, and the subsequent analysis of SPP coupling and decay at gold and semiconductor surfaces.

Which keywords best characterize this work?

Surface Plasmon Polaritons, THz spectroscopy, Drude model, thin films, aperture coupling, and field confinement.

Why is the THz frequency range particularly significant for this study?

The THz range presents a unique spectral gap where traditional electronic and optical generation techniques are less efficient, making it a frontier for exploring resonant molecular transitions and new sensing capabilities.

How does dielectric coating influence the SPPs observed on gold?

Dielectric coating leads to a drastic reduction in the decay length of the SPP into air, resulting in much stronger confinement to the conductor surface, which enhances sensitivity for thin film spectroscopy.