Femtosecond optical spectroscopy of fullerites

The spectral dependence of ultrafast relaxation of excitations in a C60 thin film was discovered with the help of femtosecond laser spectroscopy. The dependence can be explained by the relaxation of excitations in different energy bands. The temporal dependence of photoinduced darkening is characterized by peak at delays of the order of pulse duration (approximately 50 fs). The peak is replaced at greater delays by a decrease with characteristic times (tau) 1 equals 0.4 ps and (tau) 2 equals 30 ps, determined by the relaxation of electrons on intramolecular and intermolecular oscillations. The spectral dependence of two- photon absorption is investigated.