Thermo-optic tuning of directional infrared emissivity

TL;DR

This paper demonstrates thermo-optic tuning of infrared emissivity using InAs-based materials, enabling adjustable directional thermal emission over a broad wavelength range for applications like thermophotovoltaics and thermal imaging.

Contribution

It introduces a novel thermo-optic approach with InAs-based gradient ENZ materials for broadband directional thermal emitters with tunable angular selectivity.

Findings

Achieved 5° and 10° increase in directional emissivity angular extent.

Demonstrated tuning across 12.5 to 15 μm wavelength range.

Operated at moderate temperatures below 400 K.

Abstract

Tuning the spatial extent of directional thermal emission across an arbitrary, and fixed spectral bandwidth is a fundamentally enabling capability for a range of emerging applications such as thermophotovoltaics, thermal imaging, and radiative cooling. However, previous experimental demonstrations were limited to narrow bandwidths, and the resonance frequency itself changed significantly as a function of the reconfigured directional response. Here, we demonstrate thermo-optic tuning of directional infrared emissivity using InAs-based gradient ENZ materials functioning as broadband directional thermal emitters whose angular selectivity can be modified via thermal free-carrier effects. We experimentally demonstrate two emitters achieving a 5{\deg} and 10{\deg} increase in the angular extent of their directional emissivity in the p-polarization across a prescribed, broad wavelength range of operation (12.5 to 15$\mu$m), for moderate temperatures below 400 K. Temperature-driven control of directional emissivity offers a new mode of post-fabrication control of radiative heat transfer that may in turn enable novel device functionalities.