Third-Order Nonlinear Optical Response of Fullerenes as a Function of the Carbon Cage Size (C₆₀ to C₉₆) at 0.532 μm

We report the results of our degenerate four-wave-mixing measurements (DFWM) on the fullerene series from C 60 to C 96 dissolved in CS 2 . The DFWM measurements were carried out using 70 ps laser pulses at the wavelength of 0.532 μm under the optimized experimental conditions. The second hyperpolarizabilities γ 1111 of all these fullerenes were determined to be on the order of 10 -31 −10 -30 esu, and overall they increase smoothly with the carbon cage size except for C 70 and C 78, which show anomalously larger γ 1111 values than those of their neighboring cage sizes we investigated. The number of π-conjugated electrons, geometrical structure, and resonance enhancement are discussed as possible factors responsible for the observed third-order optical nonlinearities of the fullerenes.