Enhancing the Nonlinear Optical Response in Metasurfaces using Epsilon-Near-Zero Materials Open Access

Abstract

The creation of strong nonlinear optical effects is essential for the advancement of

nanophotonic devices. These devices are often limited in efficiency and form-factor

due to the high excitation powers and long propagation lengths required by tradi-

tional materials. This thesis explores the integration of an ENZ material, indium tin

oxide (ITO), into a metasurface geometry with a goal to enhance nonlinear responses,

specifically focusing on third harmonic generation (THG). ENZ materials exhibit an

array of tunable field enhancement properties stemming from the real part of their

permittivity becoming vanishingly small near the ENZ wavelength.

We combine simulations with experimental measurements to design, fabricate,

and characterize the ENZ-based metasurface. The proposed metasurface achieved an

estimated normalized THG conversion efficiency of 4.18 × 10^−9 W^−2; over two orders

of magnitude larger than previously published results from a similar metasurface

without an ENZ material. Distinct long temporal dynamics were also observed on

resonance, further indicating the impact of ITO on the nonlinear response.

The results of this thesis demonstrate the potential of ENZ materials for signifi-

cantly enhancing nonlinear responses in nanophotonic environments that require high

tunability, low excitation powers, and a compact form-factor.

Table of Contents

Introduction Introduction to Nonlinear Optics Epsilon-Near-Zero Materials Drude Model Drude-Lorentz Model Electric Field Enhancement, Relaxed Phase Matching, High Dispersion ENZ Mode and Berreman Mode Bound States in the Continuum Symmetry Protected Bound State in the Continuum Accidental Bound State in the Continuum True BIC vs. Quasi-BIC Material and Structure Marriage Combining Intrinsic and Extrinsic Factors Materials and Methods Simulations COMSOL Multiphysics and RETICOLO Simulation Methods Experimental Methods Sample Fabrication Linear Measurements Nonlinear Measurements Pump-Probe Measurements Results Conclusion and Next Steps Bibliography

About this Master's Thesis

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School	Laney Graduate School
Department	Physics
Degree	M.S.
Submission	Master's Thesis
Language	English
Research Field	Physics, Condensed Matter Physics, Electricity and Magnetism Physics, Optics
Keyword	Nanophotonics Nonlinear Optical epsilon-near-zero Metasurfaces
Committee Chair / Thesis Advisor	Hayk Harutyunyan, Emory University
Committee Members	Lili Wang, Emory University Wladimir Benalcazar, Emory University Sergei Urazhdin, Emory University

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