The optical properties of single-wall carbon nanotube sheets in the far-infrared (FIR) have been investigated with THz time-domain spectroscopy. Over a wide frequency range from 1 to 40 THz, the complex dielectric function of the nanotube sample has been derived. Our data can be excellently reproduced by a model based on a Drude and a Lorentz contribution to the overall signal. The extracted fit parameters such as Drude scattering rate and Lorentz center frequency are consistent with values obtained by scanning tunneling techniques. Our results show that direct optical transitions in small band gap tubes as expressed by the Lorentzian part dominate the FIR absorption properties of carbon nanotubes with tube species of different electric properties.
The publication is available at link DOI 10.1002/pssb.200776112