4nm single-walled carbon nanotubes ( SWNTs ) of three possible structures were fabricated. The
frequency-domain transmission spectrum of SWNTs was obtained by Fourier transform in terahertz time-domain
spectroscopy (THz-TDS) system. By analyzing the spectrum, we can see that the absorption coefficient of SWNTs
augments with an increase in the frequency. It increases slowly at low frequency, and almost be linear. But after 1.1THz,
the absorption coefficient rises rapidly with the frequency. The result is generally corresponding with the theory
Drude-Lorentz model combined with the Maxwell-Garnett model. But there is some difference at low frequency, further
discuss is needed.