Tunable highly reflective metasurfaces
International team led by Leibniz University Hannover researchers demonstrate wavelength-selective metamirrors based on sapphire and silicon nanoparticles
Metasurfaces are sheet materials with artificial structures smaller than the electromagnetic wavelength with which the surface interacts. In recent years, significant progress has been made in the analytical and numerical study of highly reflective metasurfaces. A new study led by researchers at the Institute for Gravitational Physics at Leibniz University Hannover, Germany, presents the first experimental validation of the feasibility of realizing a reflective metasurface at selected wavelengths. The metasurface presented in this study is based on a single-layer nanoparticle array consisting of silicon cylinders on a sapphire substrate. It can be tuned and optimized to exhibit the desired behavior: to be highly reflective at wavelengths of 1064 nm or 1550 nm. The fabricated structures have a reflectivity of about 95%, which can be improved by further optimization of the fabrication and characterization processes. The current technology lays the foundation for the development and realization of other potential metasurface designs. This technology has the potential to be used in future gravitational-wave detectors. There, single-layer reflective surfaces mitigate coating thermal noise, an important source of instrumental disturbance.
Paper abstract
The increasing demand for novel mirror coating designs for new generation of gravitational wave detectors is stimulating significant research interest in investigations of reflective properties of metasurfaces. Given this strong interest, this article details a systematic methodology for fabricating reflecting metasurfaces (metamirrors) designed to operate at target wavelengths of 1064 or 1550 nm. The proposed metasurfaces consist of silicon cylindrical nanoparticles placed on a sapphire substrate. First, the dimensional parameters of the structures are thoroughly selected through numerical simulations combined with material characterization. The configurations are subsequently analyzed analytically to reveal the mirror effect, which arises from the excitation of electric and magnetic dipole moments. Following this, the metasurfaces are fabricated and experimentally characterized, demonstrating reflectivity exceeding 95% around the design wavelengths, which is in good agreement with theoretical predictions. Overall, the work demonstrates the feasibility and detailed methodology for the fabrication of thin, lightweight metamirrors capable of achieving near-perfect reflectivity at the specified target wavelengths.
