Non-diffraction-limited hyperbolic metamaterials are not only finding applications as hyperlenses and photonic funnels but can also be used as highly efficient radiation absorbers, with nearly all incident light "sucked" into the metamaterial medium. The material was predicted by Purdue University (West Lafayette, IN) researcher Evgenii Narimanov and demonstrated by researchers at Norfolk State University (Norfolk, VA). Because a uniaxial dielectric metamaterial can be designed such that one of the components of the dielectric permittivity tensors is negative, that metamaterial can have an infinite value of the density of states for every frequency where different components of the dielectric permittivity have opposite signs. This infinite density of states dramatically suppresses light scattering from the metamaterial.
Radiation absorption was experimentally verified using a hyperbolic metamaterial consisting of arrays of 35 nm thick silver (Ag) nanowires (with dimensions 1 cm × 1 cm × 51 µm) grown in anodic alumina membranes using an electroplating technique. After filling with Ag and adding surface-roughness treatments, reflectance was significantly reduced to less than 1% at an 873 nm wavelength. While comparable to the darkest media available so far, such as carbon nanotubes or other traditional nonreflective coatings, the unique feature of the new metamaterial is its ability to not only sustain but even see improved performance if damaged in a real-life environment. Contact Mikhail A. Noginov at [email protected].