Graphene Nano-Optics in the Terahertz Gap

Graphene nano-optics at terahertz (THz) frequencies (nu) is theoretically anticipated to feature extraordinary effects. However, interrogating such phenomena is nontrivial, since the atomically thin graphene dimensionally mismatches the THz radiation wavelength reaching hundreds of micrometers. Greater challenges happen in the THz gap (0.1-10 THz) wherein light sources are scarce. To surpass these barriers, we use a nanoscope illuminated by a highly brilliant and tunable free-electron laser to image the graphene nano-optical response from 1.5 to 6.0 THz. For nu < 2 THz, we observe a metal-like behavior of graphene, which screens optical fields akin to noble metals, since this excitation range approaches its charge relaxation frequency. At 3.8 THz, plasmonic resonances cause a field-enhancement effect (FEE) that improves the graphene imaging power. Moreover, we show that the metallic behavior and the FEE are tunable upon electrical doping, thus providing further control of these graphene nano-optical properties in the THz gap.

Automated summary

In this study, we used a highly brilliant and tunable free-electron laser to illuminate a nanoscope and observe the graphene nano-optical response from 1.5 to 6.0 THz. At frequencies below 2 THz, graphene exhibited a metal-like behavior and screened optical fields similar to noble metals. At 3.8 THz, plasmonic resonances caused a field-enhancement effect that improved the imaging power of graphene. Furthermore, we demonstrated tunability of the metallic behavior and the field-enhancement effect through electrical doping, providing additional control over graphene's nano-optical properties in the THz gap.