Direct laser writing of electromagnetic metasurfaces for infra-red frequency range

Electromagnetic metasurfaces allow realization of various photonic functionalities using sub-wavelength thick layers of artificially structured material. Recently, metasurfaces consisting of three-dimensional metallic inclusions arranged into two-dimensional periodic arrays were proposed as a way to realize metasurfaces that have no ground plane and are optically transparent in a wide spectral range. However, practical patterning of such structures is beyond the reach of traditional planar patterning techniques. To address this challenge, we have employed femtosecond direct laser write (DLW) technique combined with simple metallization process. Here, we report fabrication and properties of functional metasurfaces consisting of metallic helices and vertical split-ring resonators that can be used as perfect absorbers and polarization converters. In accordance with theoretical predictions, our samples exhibit perfect absorption resonances tunable in the wavelength range of 4:5 - 9:2 mu m by scaling the unit cell size. Perfect absorber structures exhibit polarization and incidence angle-invariant operation with measured absorbance in excess of 0.85 for incidence angles up to 30 degrees. Similar structures may find applications innarrow-band infra-red detectors and emitters, spectral filters, and be combined into multi-functional, multi-layered structures.