Terahertz Harmonic Generation from Graphite Pencil Drawings

The third harmonic generation (THG) of graphite layers on paper substrate upon excitation with intense (up to 100 kV cm(-1)) narrowband terahertz (THz) pulses is studied. Highest THG efficiencies are comparable with those of chemical vapor deposition-grown single-layer graphene. Samples are hand drawn, using commercially available pencils. The THG response shows high sensitivity regarding the hatching direction relative to the THz polarization orientation. Using Raman spectroscopy, the occurrence of graphene-like structures in the samples is confirmed. The findings demonstrate the feasibility of virtually no-cost and easy-to-fabricate materials for THz nonlinear optics.