Martín-Sánchez Javier, Duan Jiahua, Taboada-Gutiérrez Javier, Álvarez-Pérez Gonzalo, Voronin Kirill V, Prieto Iván, Ma Weiliang, Bao Qiaoliang, Volkov Valentyn S, Hillenbrand Rainer, Nikitin Alexey Y, Alonso-González Pablo
Department of Physics, University of Oviedo, Oviedo, Spain.
Center of Research on Nanomaterials and Nanotechnology, CINN (CSIC-University of Oviedo), El Entrego 33940, Spain.
Sci Adv. 2021 Oct 8;7(41):eabj0127. doi: 10.1126/sciadv.abj0127.
Phonon polaritons (PhPs)—light coupled to lattice vibrations—with in-plane hyperbolic dispersion exhibit ray-like propagation with large wave vectors and enhanced density of optical states along certain directions on a surface. As such, they have raised a surge of interest, promising unprecedented manipulation of infrared light at the nanoscale in a planar circuitry. Here, we demonstrate focusing of in-plane hyperbolic PhPs propagating along thin slabs of α-MoO. To that end, we developed metallic nanoantennas of convex geometries for both efficient launching and focusing of the polaritons. The foci obtained exhibit enhanced near-field confinement and absorption compared to foci produced by in-plane isotropic PhPs. Foci sizes as small as λ/4.5 = λ/50 were achieved (λ is the polariton wavelength and λ is the photon wavelength). Focusing of in-plane hyperbolic polaritons introduces a first and most basic building block developing planar polariton optics using in-plane anisotropic van der Waals materials.
声子极化激元（PhPs）——与晶格振动耦合的光——具有面内双曲线色散，表现出沿表面特定方向的大波矢类射线传播以及增强的光学态密度。因此，它们引发了人们极大的兴趣，有望在平面电路中对纳米尺度的红外光进行前所未有的操控。在此，我们展示了沿α-MoO薄平板传播的面内双曲线PhPs的聚焦。为此，我们开发了凸面几何形状的金属纳米天线，用于极化激元的高效发射和聚焦。与面内各向同性PhPs产生的焦点相比，所获得的焦点表现出增强的近场限制和吸收。实现了小至λ/4.5 = λ/50的焦点尺寸（λ为极化激元波长，λ为光子波长）。面内双曲线极化激元的聚焦引入了使用面内各向异性范德华材料发展平面极化激元光学的首个也是最基本的构建模块。
