Metasurface makes thermal sources emit laser-like light

Amazing stuff!

"... the new metasurface uses a periodic structure with tailored local perturbations to transform ordinary thermal emissions into something more like a laser beam – an achievement heralded as “just the beginning” for thermal radiation control. ...

The final structure was made from silicon and structured as an array of rectangular pillars (for the non-local interactions) interspersed with elliptical pillars (for the asymmetric emission). Using this structure, the team demonstrated coherent directed emission for six different polarizations, at frequencies of their choice. They also used it to send circularly polarized light in arbitrary directions, and to split thermal emissions into orthogonally polarized components travelling in different directions. While this so-called photonic Rashba effect has been demonstrated before in circularly polarized light, the new thermal metasurface produces the same effect for arbitrary polarizations – something not previously thought possible. ..."

"In a groundbreaking advancement, researchers with the CUNY ASRC have experimentally demonstrated that metasurfaces (two-dimensional materials structured at the nanoscale) can precisely control the optical properties of thermal radiation generated within the metasurface itself. ...

Metasurfaces offer a solution for greater utility by controlling electromagnetic waves through meticulously engineered shapes of nanopillars that are arrayed across their surfaces. By varying these structures, researchers can achieve control over light scattering, effectively “shaping” light in customizable ways. ...

While conventional thermal radiation is unpolarized, a significant focus of the research was enabling thermal radiation with circularly polarized light, where the electric field oscillates in a rotating manner. Recent works had shown that opposite circular polarizations (rotating respectively with left-handed and right-handed features) could be split into opposite directions, but there seemed to be a fundamental limit to further control the polarization of emitted light. The team’s new design transcends this limitation, allowing for asymmetric emission of circular polarization towards a single direction, demonstrating full control over thermal emission. ..."

From the abstract:

"Thermal emission from a hot body is inherently challenging to control due to its incoherent nature. Recent advances have shown that patterned surfaces can transform thermal emission into partially coherent beams with tailored directionality and frequency selectivity. Here we experimentally demonstrate polarization-selective, unidirectional and narrowband thermal emission using single-layer metasurfaces. By implementing polarization gradients across the surface, we unveil a generalization of the photonic Rashba effect from circular polarizations to any pair of orthogonal polarizations and apply it to thermal emission. Leveraging pointwise specification of arbitrary elliptical polarization, we implement a thermal geometric phase and leverage it to prove previous theoretical predictions that asymmetric chiral emission is possible without violating reciprocity. This general platform can be extended to other frequency regimes in efforts to compactify metasurface optics technologies without the need for external coherent sources."

Metasurface makes thermal sources emit laser-like light – Physics World

Researchers Demonstrate Metasurfaces That Control Thermal Radiation in Unprecedented Ways (original news release) "The advance shows promise for creating compact, inexpensive, and portable light sources, which are crucial for space-based applications, biological and geological field research, and military operations."

Local control of polarization and geometric phase in thermal metasurfaces (no public access, but article above contains link to PDF)

Thermal emission control: A thermal metasurface is made of a single layer of nanostructured silicon (gray) on top of glass (blue) and a metal mirror. The nanostructured surface is tailored so that it thermally emits circularly polarized light in the desired direction.