Vertical split-ring resonator perfect absorber metamaterial for IR frequencies realized via femtosecond direct laser writing

Perfect electromagnetic metamaterial absorbers based on three-dimensional (3D) vertical split-ring resonators for an infrared spectral range were fabricated using a combination of high-resolution direct laser write lithography and a simple metalization by sputtering. In accordance with theoretical predictions, the fabricated samples exhibit perfect absorption resonances tunable in the wavelength range of 4.5–9.2 µm by changing the dimensions and spacing of the resonators. The structures exhibit polarization and incidence angle-invariant operation with absorbance in excess of 0.85 for incidence angles up to 30°. In the future, they may find applications as narrow-band thermal emitters and for signal enhancement in mid-IR photodetectors.