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Leveraging Phonon Polariton Modes in Polar Materials for Selective Thermal Emission and Absorption

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posted on 2021-11-09, 00:00 authored by Irfan Khan

The growing interest in the mid-infrared portion of the electromagnetic spectrum, 3–30 µm, is due in large part to the potential for advancing applications in spectroscopy and sensing, optical free-space and on-chip communications, and passive radiative cooling. Much of the recent progress made in these areas have leveraged surface plasmon polaritons in metals and doped semiconductors at shorter wavelengths (λ < 10 µm). Recent efforts have also used surface phonon polaritons (SPhPs) as well as the epsilon-near-zero (ENZ) response of polar materials to increase light-matter interaction at longer wavelengths, but this work is limited due to the lack of an optical infrastructure at these wavelengths.

In this thesis, we leverage both the SPhP modes in nanoparticles (NPs) and the Berreman mode in ENZ films to realize selective thermal emission and absorption. We identify and characterize SPhP modes in finite crystals of ZnO. We model the absorption of ZnO NPs using Mie theory and Discrete Dipole Approximation (DDA) method. We characterize these nanoparticles experimentally using FTIR spectroscopy. We study and discuss the effects of anisotropy, surrounding medium, temperature, shape, and agglomeration of the nanoparticles on the SPhP modes.

We also demonstrate coupling to and control over the broadening and dispersion of the Berreman mode in sub-wavelength films of AlN, a mid-infrared ENZ material. By engineering the dielectric environment above and below the ENZ film, we demonstrate the ability to engineer many aspects of the optical characteristics of the Berreman mode including resonant frequency, coupling strength, broadening, and dispersion.

Finally, we experimentally evaluate the role of ENZ substrates on the thermal emission profile of multi-mode optical antennas and provide a platform for engineering both the spectral response as well as the radiation pattern. We leverage the coupling between the Berreman mode and the resonant mode of the antenna to obtain narrowband normal thermal emission with higher spacial coherence.

The work presented here could lead to new ways of engineering absorption, emission, and scattering in the mid- and far-infrared and offers an approach to make novel narrowband infrared sources and detectors.

History

Date Modified

2021-12-09

Defense Date

2021-08-23

CIP Code

  • 14.1001

Research Director(s)

Anthony J. Hoffman

Committee Members

Scott Howard Ryan K. Roeder David Burghoff

Degree

  • Doctor of Philosophy

Degree Level

  • Doctoral Dissertation

Alternate Identifier

1287936739

Library Record

6153641

OCLC Number

1287936739

Program Name

  • Electrical Engineering

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