The Measurement of Near-Field Thermal Emission Spectra using an Infrared Waveguide

TL;DR

This paper introduces a simple infrared waveguide method to measure near-field thermal emission spectra, revealing narrow peaks from surface phonon-polaritons and broadband hyperbolic modes in various materials.

Contribution

It presents a novel, robust measurement technique using an internal reflection element as an infrared waveguide for near-field thermal emission spectra.

Findings

Spectrally-narrow peaks from surface phonon-polaritons in quartz and silica

Broadband hyperbolic modes in hexagonal boron nitride

Theoretical modeling with fluctuational electrodynamics and Green's functions

Abstract

We describe a simple and robust method using an internal reflection element acting as an infrared waveguide to measure the spectra of near-field thermal emission. We experimentally demonstrate the spectrally-narrow peaks of near-field thermal emission by isotropic media due to the excitation of surface phonon-polaritons in quartz and amorphous silica and due to the frustrated total-internal-reflection modes in amorphous silica and polytetrafluoroethylene. Additionally, we demonstrate the broadband near-field thermal emission of hyperbolic modes in hexagonal boron nitride which is an anisotropic uniaxial medium. We also present a theoretical approach based on the fluctuational electrodynamics and dyadic Green's functions for one-dimensional layered media for accurate modeling of the measured spectra.