Measurement of the optical properties of graphene from THz to near-IR

We present experimental results on the optical absorption spectrum of graphene from near-IR to THz frequencies for the first time. At near-IR and mid-IR wavelengths the interband optical absorption is found to have a flat spectrum consistent with the relativistic massless Dirac-Fermion energy dispersion relation of electrons and holes in graphene. At THz frequencies intraband absorption dominates and is well described by a plasmon model. We relate the measured optical features to the dispersion of electrons, holes, and plasmons in graphene.