Terahertz Bessel metalens with an extended non-diffractive length and a high efficiency

In this paper, we propose a reflective terahertz (THz) Bessel metalens that utilizes polarization-insensitive sub-wavelength metal resonator-dielectric-metal structures. The Bessel metalens is configured with the superposition of hyperboloidal and conical phase profiles, resulting in a high-efficiency and long non-diffractive length Bessel beam. Our experimental results demonstrate that the proposed Bessel metalens has a focusing efficiency of 72.1% and a non-diffractive length of 239λ. This device has promising aspects in the fields of THz imaging systems and other miniaturized and integrated scenes that require non-diffractive Bessel beams.