Manipulating coherence of near-field thermal radiation in time-modulated systems

TL;DR

This paper demonstrates that time-modulated photonic systems can actively control the spatial coherence and frequency correlations of near-field thermal radiation, enabling new applications in thermal management and emission control.

Contribution

The authors develop a fluctuational electrodynamics framework for time-modulated systems, revealing unique coherence and correlation effects not present in static systems.

Findings

Time modulation transfers coherence between different frequencies.

Correlations between different frequency components are enabled.

Decay rates of optical emitters can be dynamically controlled.

Abstract

We show that the spatial coherence of thermal radiation can be manipulated in time-modulated photonic systems supporting surface polaritons. We develop a fluctuational electrodynamics formalism for such systems to calculate the cross-spectral density tensor of the emitted thermal electromagnetic fields in the near-field regime. Our calculations indicate that, due to time-modulation, spatial coherence can be transferred between different frequencies, and correlations between different frequency components become possible. All these effects are unique to time-modulated systems. We also show that the decay rate of optical emitters can be controlled in the proximity of such time-modulated structure. Our findings open a promising avenue toward coherence control in thermal radiation, dynamical thermal imaging, manipulating energy transfer among thermal or optical emitters, efficient near-field radiative cooling, and engineering spontaneous emission rates of molecules.