Dual-Band Terahertz Auto-Focusing Airy Beam Based on Single-Layer Geometric Metasurfaces with Independent Complex Amplitude Modulation at Each Wavelength

The Airy beam has attracted considerable interests due to its remarkable non-diffracting, self-bending, and self-healing properties. An auto-focusing Airy (AFA) beam can be achieved by constructing two counter-propagation Airy beams, which is a novel method to generate focusing effect. Traditionally, because of the complexity of the generation mechanism, it is hard to realize the Airy beam with complex amplitude modulation. The reported ones usually require bulky optical systems and typically work at one single wavelength. Here, a general scheme is proposed to launch dual-band Airy and AFA beams based on the single-layer geometric metasurface, consisting of a newly designed meta-atom that can realize independent complex amplitude modulations at two arbitrary terahertz wavelengths. Based on the proposed meta-atom, the aforementioned attractive properties of the Airy beam are demonstrated at two terahertz wavelengths. Besides, the dual-band AFA beams are illustrated to have the practically important adjustability of the focal length. Furthermore, owing to the self-healing property, the proposed focusing scheme (i.e., AFA beam) shows a much better capability of circumventing the PEC obstacles compared to the conventional metalens, which could have potential applications in various important scenarios such as biomedical imaging/therapy and nondestructive evaluation with compact size and multiwavelength functionalities.