Nakao Haruaki, Kondoh Satoshi, Suzuki Takehito
Appl Opt. 2021 May 1;60(13):3989-3996. doi: 10.1364/AO.420836.
Terahertz continuous-wave (CW) sources oscillating around the 1.0 THz band at room temperature have rapidly been developed to bridge the terahertz gap. However, reflectionless metasurfaces suitable for integration with terahertz CW sources as optical components have yet to be developed in the terahertz gap. Here, we propose a terahertz-focusing metalens consisting of reflectionless meta-atoms with a discrete distribution of negative refractive indices from ${-}{1.1}$ to ${-}{2.8}$. The proposed 2D gradient-refractive-index metalens converts an incident terahertz Gaussian beam to a line focus. We also experimentally demonstrate a metasurface of reflectionless meta-atoms with a negative refractive index of ${-}{2.8}$ adopted in the periphery of the metalens. The reflectionless metasurface in the terahertz gap would be a welcome contribution to the rapid growth of terahertz industrial applications with terahertz CW sources. Further, the design approach based on reflectionless meta-atoms with negative refractive indices could be applied to various 2D planar optical components with attractive functionalities such as collimating, arbitrary wavefront shaping, and light vortices.
室温下在1.0太赫兹频段附近振荡的太赫兹连续波（CW）源已迅速发展，以弥合太赫兹间隙。然而，在太赫兹间隙中，尚未开发出适合与太赫兹连续波源集成作为光学元件的无反射超表面。在此，我们提出一种太赫兹聚焦金属透镜，它由具有从 -1.1到 -2.8的离散负折射率分布的无反射元原子组成。所提出的二维梯度折射率金属透镜将入射的太赫兹高斯光束转换为线焦点。我们还通过实验展示了在金属透镜周边采用的具有 -2.8负折射率的无反射元原子超表面。太赫兹间隙中的无反射超表面将对太赫兹连续波源的太赫兹工业应用的快速发展做出有益贡献。此外，基于具有负折射率的无反射元原子的设计方法可应用于各种具有诸如准直、任意波前整形和光涡旋等吸引人功能的二维平面光学元件。
