Nonlinear optical properties of the fullerenes ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{70}$ at 1.064 μm

Time-resolved degenerate-four-wave-mixing experiments were conducted on films of pure ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{70}$ using a 35-ps laser at 1.064 μm. The fullerenes exhibit a two-photon resonantly enhanced third-order optical response that is primarily laser-pulse-limited. At high laser intensities, a fifth-order component to the nonlinear optical signal is observed and is attributed to a two-photon excited-state transient grating. The large two-photon absorption coefficients measured for ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{70}$ at 1.064 μm by nonlinear transmittance are consistent with this assignment.