Multi-frequency coherent emission from superstructure thermal emitters

TL;DR

This paper demonstrates how superstructure gratings can be engineered to control the spectral and angular emission properties of thermal emitters, enabling simultaneous multi-frequency and directional emission through tailored polariton interactions.

Contribution

It introduces superstructure gratings with tailorable Bragg components that enable precise control over thermal emission spectra and angles, including the creation of polaritonic band gaps and defect states.

Findings

Superstructure gratings can launch multiple polariton frequencies simultaneously.

Design flexibility allows tailoring of emission profiles within coherence length constraints.

Strong polariton interactions lead to band gaps and defect states with specific emission properties.

Abstract

Long-range spatial coherence can be induced in thermal emitters by embedding a periodic grating into a material supporting propagating polaritons or dielectric modes. However, the emission angle and frequency cannot be defined simultaneously and uniquely, resulting in emission at unusable angles or frequencies. Here, we explore superstructure gratings (SSGs) to control the spatial and spectral properties of thermal emitters. SSGs have long-range periodicity, but a unit cell that provides tailorable Bragg components to interact with light. These Bragg components allow simultaneous launching of polaritons with different frequencies/wavevectors in a single grating, manifesting as additional spatial and spectral bands upon the emission profile. As the unit cell period approaches the spatial coherence length, the coherence properties of the superstructure will be lost. Whilst the 1D k-space representation of the grating provides insights into the emission, the etch depth of the grating can result in strong polariton-polariton interactions. An emergent effect of these interactions is the creation of polaritonic band gaps, and defect states that can have a well-defined frequency and emission angle. In all, our results show experimentally how even in simple 1D gratings there is significant design flexibility for engineering the profile of thermal emitters, bound by finite coherence length.