2ND-HARMONIC SPECTROSCOPY OF FULLERENES

Optical second-harmonic generation spectra of C-60 and C-70 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 th an in linear absorption spectra of fullerene solids. We discuss the as signment of the resonances. Allowed and electric dipole forbidden tran sitions are observed for C-60. The resonances observed for C-70 are ve ry weak. Efficient quenching of the signal by the population of excito nic states is observed only for the lowest observed resonance of C-60 at 1.18 eV. (C) 1998 Elsevier Science B.V. All rights reserved.