Schiattarella Chiara, Di Gaspare Alessandra, Viti Leonardo, Justo Guerrero M Alejandro, Li Lianhe H, Salih Mohammed, Davies A Giles, Linfield Edmund H, Zhang Jincan, Ramezani Hamideh, Ferrari Andrea C, Vitiello Miriam S
NEST, CNR-NANO and Scuola Normale Superiore, 56127, Pisa, Italy.
School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, UK.
Sci Rep. 2024 Jul 14;14(1):16227. doi: 10.1038/s41598-024-62787-5.
Optical resonators are fundamental building blocks of photonic systems, enabling meta-surfaces, sensors, and transmission filters to be developed for a range of applications. Sub-wavelength size (< λ/10) resonators, including planar split-ring resonators, are at the forefront of research owing to their potential for light manipulation, sensing applications and for exploring fundamental light-matter coupling phenomena. Near-field microscopy has emerged as a valuable tool for mode imaging in sub-wavelength size terahertz (THz) frequency resonators, essential for emerging THz devices (e.g. negative index materials, magnetic mirrors, filters) and enhanced light-matter interaction phenomena. Here, we probe coherently the localized field supported by circular split ring resonators with single layer graphene (SLG) embedded in the resonator gap, by means of scattering-type scanning near-field optical microscopy (s-SNOM), using either a single-mode or a frequency comb THz quantum cascade laser (QCL), in a detectorless configuration, via self-mixing interferometry. We demonstrate deep sub-wavelength mapping of the field distribution associated with in-plane resonator modes resolving both amplitude and phase of the supported modes, and unveiling resonant electric field enhancement in SLG, key for high harmonic generation.
光学谐振器是光子系统的基本组成部分，可用于开发一系列应用的超表面、传感器和传输滤波器。亚波长尺寸（<λ/10）的谐振器，包括平面分裂环谐振器，因其在光操纵、传感应用以及探索基本光与物质耦合现象方面的潜力而处于研究前沿。近场显微镜已成为亚波长尺寸太赫兹（THz）频率谐振器模式成像的重要工具，这对于新兴的太赫兹器件（如负折射率材料、磁镜、滤波器）以及增强光与物质相互作用现象至关重要。在此，我们通过散射型扫描近场光学显微镜（s-SNOM），采用单模或频率梳太赫兹量子级联激光器（QCL），在无探测器配置下，通过自混合干涉测量法，对嵌入谐振器间隙中的单层石墨烯（SLG）的圆形分裂环谐振器所支持的局域场进行相干探测。我们展示了与面内谐振器模式相关的场分布的深亚波长映射，解析了所支持模式的幅度和相位，并揭示了单层石墨烯中谐振电场增强现象，这是高次谐波产生的关键。
