Dynamic terahertz polarization in single-walled carbon nanotubes

Single-walled carbon nanotubes SWNTs have attracted much attention owing to their striking chemical and physical properties 1 and their potential applications in nanoelectrics and biosensors. 1–3 Like other low-dimensional materials, including organic polymers, organic small molecular crystals, or quantum dot chains, 4–6 this quasi-one-dimensional material has intrinsically anisotropic physical properties. Anisotropy in the dielectric properties of SWNTs at visible and near-infrared frequencies has recently attracted much attention 7–11 and aligned SWNTs have been shown to act as effective terahertz THz polarizers. 12 An understanding of transient anisotropy in the dielectric response in SWNTs is of importance for the design of new ultrafast devices. Current high-speed devices based on inorganic semiconductor technology are limited to operating at frequencies below 100 GHz. Technologies based on SWNTs have the potential to revolutionize high-speed optoelectronic devices and achieve operating frequencies in the THz band. Therefore it is important to characterize the electrical and optical properties of SWNTs at THz frequencies. Optical pump THz probe spectroscopy OPTPS is an ideal tool for investigating such materials. The technique can be used to measure the complex dielectric response of a material over a wide frequency band on picosecond time scales after optical excitation.