DISPERSION OF THE 3RD-ORDER OPTICAL NONLINEARITY OF C-60 - A 3RD-HARMONIC GENERATION STUDY

We report the \chi(3)(-3-omega; omega, omega, omega)\ of a thin film of polycrystalline C60 on glass measured over the fundamental energy range of 0.52-1.18 eV. The dispersion clearly shows a three-photon resonance at HBAR-omega=0.94 eV, whose third-harmonic energy corresponds to the dipole allowed transition at 2.8 eV in the solid C60. The dispersion can be fit by a two-level model, and a good correlation exists between the nonlinearity and the linear optical absorption spectrum. Away from resonance, \chi(3)(-3-omega; omega, omega, omega) \= (4.1 +/- 0.6) x 10(-12) esu, while at the peak, \chi(3)(-3-omega; omega, omega, omega)\ = (2.7 +/- 0.4) x 10(-11) esu.