Terahertz Imaging and Spectroscopy of Large-Area Single-Layer Graphene

The high electron mobility of graphene points to potential for high-speed electronic and opto-electronic devices operating at terahertz (THz) switching rates. Therefore, there is great interest in probing the electronic properties of large-area graphene at ultrafast time scales. We have demonstrated THz imaging and spectroscopy of a 15x15-mm$^{2}$ single-layer graphene film using broadband THz pulses. The THz images clearly map out the THz carrier dynamics of the graphene-on-Si sample, allowing us to measure sheet conductivity with sub-mm resolution without fabricating electrodes. The THz carrier dynamics are dominated by intraband transitions and the THz-induced electron motion is characterized by a flat spectral response. A theoretical analysis based on the Fresnel coefficients for a metallic thin film shows that the local sheet conductivity varies across the sample from 1.7 -- 2.4 x 10$^{-3}$ Ohm$^{-1}$ (sheet resistance 420 - 590 Ohm/sq).