A Broadband Plasmonic Metasurface Superabsorber at Optical Frequencies: Analytical Design Framework and Demonstration

摘要

Plasmonic metasurface based superabsorbers exhibit high absorbance. Whilernthe absorption peak can be tuned by the geometry/size of the sub-wavelengthrnresonator, broadband absorption can be obtained by harnessing spectrallyrnshifted resonances of multiple resonators of various size/shapes in a unit cell.rnMetal dispersion hinders high-performance broadband absorption at opticalrnfrequencies and careful designing is essential to achieve good structures.rnA novel analytical framework is proposed for designing a broadbandrnsuperabsorber which is much faster than the time consuming full-wavernsimulations that are employed so far. Analytical expressions are derived forrnthe wavelength dependency of the design parameters, which are then usedrnin the optimization of broadband absorption. Numerical simulations reportrnan average polarization-independent absorption of ≈97% in the 450–950 nmrnspectral region with a near unity absorption (99.36%) in the 500–850 nmrnregion. Experimentally, an average absorption over 98% is demonstrated in thern450–950 nm spectral region at 20° incident angle. The designed superabsorberrnis polarization insensitive and has a weak launch angle dependency. Thernproposed framework simplifies the design process and provides a quickerrnoptimal solution for high-performance broadband superabsorbers.