Third-order optical nonlinearity of the carbon nanotubes was investigated with both 30-ps-wide and 8-ns-wide Nd:YAG laser beams. Both 1064 and 532 nm were used in each case. The nonlinear optical temporal response was obtained both on the picosecond scale and on the nanosecond scale, and the corresponding mechanism is discussed. Finally, we have compared the average contribution of one carbon atom to the third-order optical nonlinearity in the carbon nanotubes with that in C60, finding some enhancement of the third-order optical nonlinearity in the carbon nanotubes.
A classical point dipole model is used to calculate the local field effect on the optical properties of adsorbed molecules on a substrate. The spatially non-varying component of the local field at the:molacules can be described by using a local-field correction factor. Equally important is the spatially varying component of the local field which arises mainly from the molecule.-substrate interaction. The rapid variation over the molecular dimension can appreciably modify the transition matrix elements and break down the electric dipole selection rules. The effect be-41 *
An improvement on the simplified theory of all-optical poling [Chem. Phys. Lett. 286, 415 (1998)] is proposed. In this improvement the influence of the cis isomer is taken into account in the process of photoinduced molecular polar alignment. An analytical expression for the induced polar order in the steady-state regime is derived. This expression shows that, although the contribution to the photoinduced second-order susceptibility from the cis state itself can be neglected, the population of the cis state plays an important role. This result suggests the possibility that one can improve the induced polar order by increasing the poling temperature, so that thermal-assisted optical poling can be explained.
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