Single-beam z-scan and transient absorption experiments were carried out be
tween 400 and 1000 nm in Gd-2 at C-80 thin films and solutions. The third-o
rder nonlinearity was large, negative, and strongly dependent on pulse dura
tion and wavelength. Transient absorption results suggest that the fast non
linear response is enhanced by two-photon-induced ground-state absorption a
nd excited-state bleaching effects. (C) 2001 American Institute of Physics.