Duan J, Álvarez-Pérez G, Tresguerres-Mata A I F, Taboada-Gutiérrez J, Voronin K V, Bylinkin A, Chang B, Xiao S, Liu S, Edgar J H, Martín J I, Volkov V S, Hillenbrand R, Martín-Sánchez J, Nikitin A Y, Alonso-González P
Department of Physics, University of Oviedo, Oviedo, Spain.
Center of Research on Nanomaterials and Nanotechnology, CINN (CSIC-Universidad de Oviedo), El Entrego, Spain.
Nat Commun. 2021 Jul 15;12(1):4325. doi: 10.1038/s41467-021-24599-3.
Refraction between isotropic media is characterized by light bending towards the normal to the boundary when passing from a low- to a high-refractive-index medium. However, refraction between anisotropic media is a more exotic phenomenon which remains barely investigated, particularly at the nanoscale. Here, we visualize and comprehensively study the general case of refraction of electromagnetic waves between two strongly anisotropic (hyperbolic) media, and we do it with the use of nanoscale-confined polaritons in a natural medium: α-MoO. The refracted polaritons exhibit non-intuitive directions of propagation as they traverse planar nanoprisms, enabling to unveil an exotic optical effect: bending-free refraction. Furthermore, we develop an in-plane refractive hyperlens, yielding foci as small as λ/6, being λ the polariton wavelength (λ/50 compared to the wavelength of free-space light). Our results set the grounds for planar nano-optics in strongly anisotropic media, with potential for effective control of the flow of energy at the nanoscale.
各向同性介质之间的折射表现为，光从低折射率介质进入高折射率介质时会向边界法线方向弯曲。然而，各向异性介质之间的折射是一种更奇特的现象，目前几乎尚未得到研究，尤其是在纳米尺度上。在这里，我们通过在天然介质α-MoO₃中利用纳米级受限极化激元，可视化并全面研究了两个强各向异性（双曲线形）介质之间电磁波折射的一般情况。当折射极化激元穿过平面纳米棱镜时，其传播方向呈现出非直观的特性，从而揭示了一种奇特的光学效应：无弯曲折射。此外，我们开发了一种面内折射超透镜，能产生小至λ/6的焦点，其中λ为极化激元波长（与自由空间光波长相比为λ/50）。我们的研究结果为强各向异性介质中的平面纳米光学奠定了基础，具有在纳米尺度上有效控制能量流动的潜力。
