Multi-frequency coherent emission from superstructure thermal emitters

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 2 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.

Collective Phonon–Polaritonic Modes in Silicon Carbide Subarrays

“…Similar to atoms in different arrangements forming molecules, interacting nanostructures in metallic complexes, such as dimers, − trimers, quadrumers, , can give rise to collective modes, enabling the design of resonant properties. More importantly, the polaritonic response of these collectively excited polaritonic modes greatly depends on the spatial arrangement of the nanostructures − as well as the intrinsic optical properties of individual elements . Similarly, to design additional LSPhP resonant properties, more repeatable elements can be added into the unit cell of the polar nanostructures (Figure a), for example, 2 × 2, 3 × 3, and 4 × 4 subarrays of nanopillars as the unit-cell basis.…”

Perspective: Phonon polaritons for infrared optoelectronics

“…Periodic nanostructures have also been proposed as the basis of a thermal lens, whose thermal emission is focussed at a well-defined height above the grating structure [113]. More sophisticated emission patterns can be realized by relaxing the periodicity of gratings, though the partial spatial coherence of the the SPhP mode needs to be accounted for in such designs [114]. Similarly to these delocalised SPhPs in periodic structures, localised SPhPs on individual polar nanoresonators can also be utilised to enhance far-field thermal emission.…”

Lifetime and Molecular Coupling in Surface Phonon Polariton Resonators

“…The lifetimes associated with SPhP modes are typically on time scales in the few to tens of picosecond range, several orders of magnitude longer than free carriers in metal. 21,22 This results in lower loss nanophotonics, which can be directly applied to realize narrowband and efficient optoelectronics 23,24 and sensor technologies. 25 Given the success of prior work exploiting SPPs for SEIRA, SPhPs have also been proposed as promising for sensing.…”

“…Of the SPhP materials, SiC is a prototypical example. , It supports SPhP modes in the spectral range between transverse optic (TO, 797 cm –1 ) and longitudinal optic (LO, 971 cm –1 ) phonon frequencies, known as a Reststrahlen band. The lifetimes associated with SPhP modes are typically on time scales in the few to tens of picosecond range, several orders of magnitude longer than free carriers in metal. , This results in lower loss nanophotonics, which can be directly applied to realize narrowband and efficient optoelectronics , and sensor technologies …”