We have investigated the third order nonlinear optical properties of carbon nanotubes thick films. Nanosecond Degenerate Four Wave Mixing (DFWM) measurements have been performed at 532 and 355 nm yielding effective χ (3) values of the order of 10-11 esu. and indicating the resonant nature of the excitation involved. The determination of the CNTs sample density by means of Scanning Electronic Microscope technique allowed to relate sample bulk properties like χ(3) to the single CNT second order polarizability coefficient. Copyright © 2003 John Wiley & Sons, Ltd.
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