Focusing of in-plane hyperbolic polaritons in van der Waals crystals with tailored infrared nanoantennas.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 34623915.
- Also identified by DOI 10.1126/sciadv.abj0127 and PMC identifier 8500510.
- Licence recorded as CC BY-NC.
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Abstract
Phonon polaritons (PhPs)—light coupled to lattice vibrations—with in-plane hyperbolic dispersion exhibit ray-like propagation with large wave vectors and enhanced density of optical states along certain directions on a surface. As such, they have raised a surge of interest, promising unprecedented manipulation of infrared light at the nanoscale in a planar circuitry. Here, we demonstrate focusing of in-plane hyperbolic PhPs propagating along thin slabs of α-MoO<sub>3</sub>. To that end, we developed metallic nanoantennas of convex geometries for both efficient launching and focusing of the polaritons. The foci obtained exhibit enhanced near-field confinement and absorption compared to foci produced by in-plane isotropic PhPs. Foci sizes as small as λ<sub>p</sub>/4.5 = λ<sub>0</sub>/50 were achieved (λ<sub>p</sub> is the polariton wavelength and λ<sub>0</sub> is the photon wavelength). Focusing of in-plane hyperbolic polaritons introduces a first and most basic building block developing planar polariton optics using in-plane anisotropic van der Waals materials.