▎ 摘　　要

Accessing the nonradiative near-field electromagnetic interactions with high in-plane momentum (q) is the key to achieve super resolution imaging far beyond the diffraction limit. At far-infrared and terahertz (THz) wavelengths (e.g., 300 mu m = 1 terahertz = 4 meV), the study of high q response and nanoscale near-field imaging is still a nascent research field. In this work, we report on THz nanoimaging of exfoliated single and multilayer graphene flakes by using a state-of-the-art scattering-type near-field optical microscope (s-SNOM). We experimentally demonstrated that the single layer graphene is close to a perfect near-field reflector at ambient environment, comparable to that of the noble metal films at the same frequency range. Further modeling and analysis considering the nonlocal graphene conductivity indicate that the high near-field reflectivity of graphene is a rather universal behavior: graphene operates as a perfect high-q reflector at room temperature. Our work uncovers the unique high-q THz response of graphene, which is essential for future applications of graphene in nano-optics or tip-enhanced technologies.