All-metallic epsilon-near-zero graded-index converging lens at terahertz frequencies

In this communication, an all-metallic epsilon-near-zero graded-index lens is demonstrated working at terahertz (THz) frequencies. The lens is designed using an array of narrow hollow rectangular waveguides working near cut-off of their fundamental mode emulating an epsilon-near-zero medium. The prototype is evaluated both experimentally and numerically demonstrating a good agreement between them with a focal length of 6 mm at the frequency of 0.675 THz. An experimental power enhancement at the focal length of 42 times is achieved compared to the case without the lens. The results presented here may open doors to the design of novel devices within the terahertz frequency range using such artificial metastructures.