We have measured the absorption and dispersion of single- walled carbon nanotubes (SWCNTs) films using an optoelectronic THz beam system for THz time-domain spectroscopy (THz- TDS). The angle-dependent conductivities of anisotropically aligned nanotube films, which were prepared by a mechanical squeezing with a bar coater, were also characterized. Samples were prepared raw SWCNT and purified SWCNT, respectively.
As the frequency increases, the power absorption coefficient of SWCNT increases. Also, the power absorption shows maximum at parallel orientation of the film to the THz beam polarization and minimum at perpendicular orientation, which was explained by a 'wire grid' model indicating that SWCNTs were aligned. The refractive indices decrease with increasing frequency. This trend is similar to that yielded by lightly doped semiconductors. The real conductivities increase with increasing frequency in the low frequency ranges. This is not congruent with the simple Drude theory.