Si3N4 Dielectric Hemi-sphere Arrayed Plasmonic Metasurface With Top Metal Coating for Multiresonant Absorption in NIR Regime
摘要
Present report focuses on the design and optical perfect absorption/reflection properties of novel plasmonic metasurface made of square array of Si3N4 hemi-spheres on flat Si3N4 surface. The whole structure is sandwiched between flat gold layer and top gold coating. Theoretical study using Finite Difference Time Domain (FDTD) computation shows multiple near perfect absorptions (80–100%) with narrow line width (~ 50 nm) between 550 to 1500 nm. Four distinct absorption peaks (or reflection dips) are observed at 1020 nm (A1), 888 nm (A2), 614 nm (A3), 740 nm (A4) which can be manipulated by varying structural parameters such as period, hemi-sphere diameter and top gold coating thickness. These multiple absorptions arise due to electric dipolar resonance, magnetic resonance, excitation of various surface plasmon modes (such as (1,0); (2,0); (1,1)) and cavity mode, as evident from near-field analysis. With appropriate structural parameters, multiband well resolved near perfect absorptions are achieved at desired wavelengths. The proposed metasurface is insensitive to the polarization of excitation beam, and has relatively large launch angle tolerance (~ 20°), making it suitable for optical and optoelectronic device integration.