Near-Unity Light-Matter Interaction in Mid-Infrared van der Waals Metasurfaces.

Accessing mid-infrared radiation is of great importance for a range of applications, including thermal imaging, sensing, and radiative cooling. Here, we study light interaction with hexagonal boron nitride (hBN) nanocavities and reveal strong and tunable resonances across its hyperbolic transition. In addition to conventional phonon-polariton excitations, we demonstrate that the high refractive index of hexagonal boron nitride outside the Reststrahlen band allows enhanced light-matter interactions in deep subwavelength (<λ/15) nanostructures across a broad 7-8 µm range. Emergence and interplay of Fabry-Perot and Mie-like resonances are examined experimentally and theoretically. Near-unity absorption and high quality (Q ≥ 80) resonance interaction in the vicinity of the hBN transverse optical phonon is further observed. Our study provides avenues to design highly efficient and ultracompact structures for controlling mid-infrared radiation and accessing strong light-matter interactions with hBN.

Ultra-wideband graphene-based absorber in the terahertz regime based on elliptical slots and a complementary sinusoidal-patterned dielectric layer.

A graphene-based absorber is presented based on elliptical slots and a complementary sinusoidal-patterned dielectric layer. The proposed absorber structure includes upper dielectric and metal film layers resulting in a Fabry-Perot cavity. The produced cavity enhances the confinement of electromagnetic waves. The presented absorber yields an absolute bandwidth of 4.02 THz (0.51-4.53 THz) considering an 0.88 absorbance level together with normal incidence. The presented structure benefits from an almost insensitive ultra-wideband absorbing performance as θ varies up to 50°and 60° for TE and TM polarizations, respectively. Moreover, the considered symmetry in the design procedure results in an almost insensitive structure with respect to the φ incident angle. Finally, the obtained 160% fractional bandwidth is much greater compared to mentioned previous works in literature.

Ultra-wideband terahertz metamaterial absorber based on Snowflake Koch Fractal dielectric loaded graphene.

In this paper, an ultra-wideband terahertz metamaterial absorber is introduced based on a Snowflake Koch Fractal (SKF) dielectric loaded on a sheet of graphene. Instead of multilayered-graphene conventional structures, a single-layered non-structured graphene absorber is presented based on gradient width modulation and cavity method. The structure of the absorber is composed of four layers, which are upper SKF dielectric and metal film layer form two mirrors of an asymmetric Fabry-Perot cavity to confine terahertz electromagnetic (EM) waves. Full wave simulations demonstrate that the proposed structure is highly efficient whereas a 161% fractional bandwidth of over 0.9 absorbance is achieved under normal incident wave considering both TE and TM polarizations. The proposed structure is polarization insensitive yielding the same absorbance for both TE and TM polarizations. The absorbance and bandwidth of the structure is almost independent of altering the incident angle θ up to 60° and 30° for TM and TE polarizations, respectively. Avoiding graphene processing and simple shape geometry are the interesting advantages of this structure resulting in feasible fabrication. The proposed structure provides much greater absorbance bandwidth in comparison to previous works.