The two-dimensional (2D) array of resonant dielectric nanostructures they describe in a paper titled "Directional lasing in resonant semiconductor nanoantenna arrays" published in Nature Nanotechnology consists of GaAs nanopillars about
250nm high and 100nm in diameter on a fused silica substrate. Under optical excitation from a 780nm pulsed femtosecond laser, light was localized within the structure by so-called Bound states In the Continuum (BICs) of coupled nanopillars, and so-called supercavities or leaky resonances where light can be amplified, were controlled by design so the light would only lase perpendicular (vertically) to the 2D array instead of diffusely across the array.
By design, the researchers were able to control the directionality of the emitted light while maintaining a high quality factor (Q = 2,750). The experiment was done at cryogenic temperatures and lasing was triggered optically by an external laser, so much work remains to make those arrays practical for integration in photonic devices (where an electrically pumped laser is preferable), but the researchers note that their design can be applied to various active high-index semiconductor materials to achieve lasing at visible and infrared wavelengths.
What's more, because the actual footprint of the sparsely distributed nanocolumns is very small on the silica substrate, this makes for a highly transparent laser structures, in excess of 85% over the 750 to 900nm emission range. This means such surface-emitting lasers could potentially be designed in multi-layered photonic devices.
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