Effect of electromagnetic radiation on an array of weakly interacting carbon nanotubes in the presence of nanosecond pulses

For metallic “zigzag”-type carbon nanotubes, the dependence of a nonlinear current on an ac electric field with an inclined-leading-edge width of $\Delta T$ = 3 $\times$ 10$^{-11}$ s and wavelength of $\lambda\approx$ 1 mm is studied. It is theoretically and numerically shown that the surface current is almost independent of the nanotube radius. In the case of semiconductor zigzag-type nanotubes, the radiation of a two-frequency CO$_2$ laser with a constant amplitude is considered as an ac electric field. The dependence on the relaxation time in the Boltzmann kinetic equation is studied. The optimal conditions for terahertz-radiation generation are achieved when the relaxation time is 40 fs. It is numerically found that the amplified radiation amplitude behaves as beats.