Second-harmonic spectroscopy of fullerenes

Optical second-harmonic generation spectra of C60 and C70 films are presented for the fundamental energy range 1.0–2.3 eV. The linewidths of the observed resonances are around 0.1 eV and thus much narrower than in linear absorption spectra of fullerene solids. We discuss the assignment of the resonances. Allowed and electric dipole forbidden transitions are observed for C60. The resonances observed for C70 are very weak. Efficient quenching of the signal by the population of excitonic states is observed only for the lowest observed resonance of C60 at 1.18 eV.