Measurement of near-field thermal emission spectra using an internal reflection element

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-internalreflection 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.

Probing Near-Field Thermal Emission of Localized Surface Phonons from Silicon Carbide Nanopillars

“…Another factor contributing to the differences between the measured and predicted spectra is related to the effect of the IRE on the captured near-field signal. As mentioned before, the measured spectra only include thermally emitted electromagnetic waves with k ρ in the range of sin (20.4°) n I k 0 < k ρ < sin (69.6°) n I k 0 . However, the simulated energy density includes contributions from all thermally emitted electromagnetic waves with any k ρ .…”

“…However, the simulated energy density includes contributions from all thermally emitted electromagnetic waves with any k ρ . Furthermore, the measured electromagnetic waves go through multiple reflections between the sample and the IRE before being captured by the FTIR spectrometer, while the theoretical energy density is simulated in a free space above the samples . The difference between the range of simulated and captured wavevectors and the multiple reflections of thermal field between the IRE and the sample result in broadening and redshift of the measured near-field peaks in comparison with the predicted spectra in the free space …”

“…The spectra of near-field thermal radiation are measured using an experimental technique utilizing an IRE for guiding the thermally emitted evanescent waves to an FTIR spectrometer . A schematic of the setup used for implementing this spectroscopy technique is shown in Figure .…”

“…It is theoretically shown that metamaterials made of nanoparticles of polaritonic materials can emit localized surface phonons (LSPhs) in their Reststrahlen band, causing narrow-band peaks in the near-field spectra. ,, It is proposed that the spectral location of the thermally emitted LSPhs can be modulated by varying the size and shape of the nanoparticles. ,, Tuning the spectrum of far-field thermal radiation by engineering the geometry of the polaritonic metamaterials has been demonstrated experimentally. ,− However, near-field thermal emission of LSPhs from polaritonic metamaterials has not been experimentally demonstrated yet. Indeed, while there have been several experimental studies on total (spectrally-integrated) near-field radiative heat transfer, ,,,− measurements of the spectrum of near-field thermal radiation have been scarce. ,− A limited number of studies have experimentally explored the near-field response of polaritonic metamaterials to an external illumination using scattering-scanning near-field optical microscopy (sSNOM). ,, Using sSNOM, an external infrared electromagnetic field is shined to an AFM tip which is located at a subwavelength distance from the metamaterials. The backscattered field from the AFM tip is guided to a Fourier transform infrared spectrometer to determine the near-field response of the metamaterials.…”

Radiative Resistance at The Nano-scale: Thermal Barrier

“…In recent years, many studies have been conducted on radiative heat transfer between objects with separation distances less than the thermal wavelength [1][2][3][4][5] . Because the radiative flux at this scale violates Stephen Boltzmann's law, heat flux management by controlling geometrical parameters and system-specific features has attracted much attention.…”