Theoretical modelling of nonlinear refraction and two-photon absorption insingle-wall carbon nanotube bundles

The nonlinear refractive index n(2) and the two-photon absorption coefficie nt alpha (2) are calculated for a bundle of diameter-distributed and aligne d single-wall carbon nanotubes. The dispersion of the nanotube circumferenc e length is shown to have important effects on the resonant behaviour of bo th quantities under consideration, giving rise to a strong broadening, inte nsity decrease, and 'red' shift of the position of the positive and negativ e resonant peaks in the n(2)(omega) and alpha (2)(omega) spectra. It is pre dicted that a relatively large refractive-index change (similar to 1 cm(2) GW(-1)) from a positive to a negative peak value produced by a relatively s mall variation of pump frequency can be achieved for real samples of carbon nanotubes in the frequency range where they are almost transparent. The re sults indicate that carbon nanotubes are a promising novel class of nanosca le materials that could be used in practical optical switching applications .