Abstract
The frequency dependence of third harmonic generation (THG) in C60 is calculated, making use of a tight-binding model for π-electrons. The magnitudes of the THG, about 10-12 esu, near zero frequency, agree with those in experiments for the low-energy region. We can also explain the order of the magnitude, 10-11 esu, around the three-photon resonance peak due to the lowest allowed excitation, recently measured by Meth et al. At higher energies, we predict a large enhancement of the THG at 3ω∼6 eV as a result of double resonance enhancement.