Terahertz Radiation from Graphite Excited by Femtosecond Laser Pulses

We experimentally investigate the terahertz (THz) generation from a graphite surface induced by femtosecond laser pulses, and systematically study the dependence on the excitation power, the crystal orientation of graphite, polarization state and incident angle of optical beam. New evidence related to excitation and detection geometry is found and presented, which supports the THz generation mechanism of transient photocarrier transporting along the basal plane normal. Our observation also suggests other probable contributions by in-plane charge oscillations. The results may be helpful to explore and understand the photoelectric properties of graphite and other allotropes of carbon.