Measurement of the Optical Absorption Spectra of Epitaxial Graphene from   Terahertz to Visible
  We present experimental results on the optical absorption spectra of epitaxial graphene from the visible to the terahertz (THz) frequency range. In the THz range, the absorption is dominated by intraband processes with a frequency dependence similar to the Drude model. In the near IR range, the absorption is due to interband processes and the measured optical conductivity is close to the theoretical value of $e^{2}/4\hbar$. We extract values for the carrier densities, the number of carbon atom layers, and the intraband scattering times from the measurements. 
Jahan M. Dawlaty, Shriram Shivaraman, Jared Strait, Paul George, Mvs   Chandrashekhar, Farhan Rana, Michael G. Spencer, Dmit...