Non-Planck thermal emission from two-level media

TL;DR

This paper presents a theoretical study showing that thermal emission from two-level media structures deviates from Planck's law and exhibits universal high-temperature behavior, impacting thermal energy applications.

Contribution

It introduces a theoretical framework for understanding non-Planckian thermal emission from two-level media in various geometries, highlighting universal high-temperature asymptotics.

Findings

Thermal emission from two-level media is fundamentally non-Planckian.

High-temperature thermal emission exhibits universal asymptotic behavior.

Results have implications for thermal energy harvesting and thermal vision systems.

Abstract

Thermal emission is a universal phenomenon of stochastic electromagnetic emission from an object composed of arbitrary materials at elevated temperatures. A defining feature of this emission is the monotonic and rapid growth of its intensity with the object's temperature for most known materials. This growth originates from the Bose-Einstein statistics of the thermal photonic field. The fact that the material's ability to absorb and emit light may change with temperature, however, is often ignored. Here, we carry out a theoretical study of thermal emission from structures incorporating ensembles of two-level media. We investigate this effect in a range of geometries including thin films and compact nanoparticles, and establish the general dependencies in the evolution of thermal emission from systems including two-level media. Thermal emission from such structures is essentially Non-Planckian and exhibits a universal asymptotic behavior in the limit of high temperatures. These results might have important implications for the design of thermal energy harvesting and thermal vision systems.