Optical properties of well-aligned multiwalled carbon nanotube bundles

The optical properties of well-aligned multiwalled carbon nanotube bundles are studied within the gradient approximation. The imaginary (real) part of the transverse dielectric function exhibits a special peak (dip) at frequency $\omega \sim 2{\gamma }_0$ $({\gamma }_0$ is the nearest-neighbor overlap integral). Consequently the loss function shows a prominent π-plasmon peak at $\omega >2\mathrm{}{\gamma }_0.$ The π plasmon also induces a strong and abrupt edge in the reflectance spectrum. These features are similar to those of graphite. The optical properties are hardly affected by the chiral angle of carbon nanotube; moreover, they are insensitive to small variation in the radius of carbon nanotube. On the other hand, the optical properties strongly depend on the polarization direction of an external electric field. The well-aligned multiwalled carbon nanotubes with high radius uniformity, which were recently reported by Fan et al. [Science 283, 512 (1999)], could be used to verify the predicted optical properties.