We demonstrate terahertz (THz) imaging and spectroscopy of a 15 × 15-mm2 single-layer graphene film on Si 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 σ(s) = 1.7 × 10(-3) to 2.4 × 10(-3) Ω(-1) (sheet resistance, ρ(s) = 420 - 590 Ω/sq).

We developed a tabletop source of intense, narrow band terahertz pulses via type-II difference-frequency generation in ZnTe crystal using two linearly chirped and orthogonally polarized optical pulses. The pulse energy is in the range of 1-3 nJ depending on the variable pulse duration from 1 to 5 ps. The amplitude of electric field reaches ϳ10 kV/ cm. The central frequency of the spectrum is continuously tunable from 0.3 to 2.5 THz with the bandwidth at 0.2-0.5 THz.