THz Emission from Graphite Surfaces

Graphite formed by Van der Waals force between adjacent graphene sheets has been studied for more than six decades due to its relatively simple quasi-two-dimensional structure. Lately, because of its close relationship to carbon nanotubes and new physics originating from graphene's linear excitation spectrum and the 4-fold degeneracy graphitic materials have attracted much of research attention. However, still little is known about the high-freqency transport properties of these materials. In this work, we investigate graphite materials in THz regime by THz emission spectroscopy. Picosecond THz pulses were observed from a highly oriented pyrolytic graphite (HOPG) surface when it was illuminated by intenseultrafast optical pulses at an oblique angle. The emission was mostly p-polarized and increased linearly with pump fluence. Several potential mechanisms for the emission including surface nonlinearility will be discussed in the talk.