The nonlinear transmission properties of C 60 and C 70 in toluene solution in the ultraviolet and visible spectral regions have been studied using nanosecond laser pulses. Whereas at 308 and 534 nm both fullerenes behave as reverse saturable absorbers, at 337 nm their behavior changes to that of a saturable absorber. A five-level rate equation model was developed that reproduces adequately the dependence of transmittance with intensity at the different irradiation wavelengths and allows us to estimate the absorption cross sections of the first excited singlet state for each fullerene.

The phase-conjugate properties of solutions of buckminsterfullerene C60 in a number of organic solvents have been investigated in the nanosecond time domain. Thermal grating established theory is shown to explain satisfactorily the experimental results, and evidence was found of the propagation in a nonlinear medium of acoustic waves generated by a nonuniform heating process, suggesting that a thermal mechanism is responsible for the long-lived component of the nonlinearity. Order of magnitude estimations of the thermally induced third-order susceptibility were obtained, and a correlation between effective thermalization yield and solvents' polarizability parameter (n 2 − 1)/(2n 2 + 1) was found.