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Bilayer Metasurfaces for Dual- and Broadband Optical Antireflection
Optical antireflection has long been
pursued for a wide range of applications, but existing approaches
encounter issues in the performance, bandwidth, and structure complexity,
particularly in the long-wavelength infrared regime. Here we present
the demonstration of bilayer metasurfaces that accomplish dual- and
broadband optical antireflection in the terahertz and mid-infrared
spectral ranges. By simply tailoring the structural geometry and dimensions,
we show that subwavelength metal/dielectric structures enable dramatic
reduction of Fresnel reflection and significant enhancement of transmission
at a substrate surface, operating either at two discrete narrow bands
or over a broad bandwidth up to 28%. We also use a semianalytical
interference model to interpret the obtained results, in which we
find that the dispersion of the constituent structures plays a critical
role in achieving the observed broadband optical antireflection