Excited-state nonlinearity measurements of ZnPcBr4/DMSO

Excited-state absorptive and refractive nonlinearities of a ZnPcBr4/DMSO solution are studied using a modified picosecond time-resolved pump-probe system based on a 4f nonlinear imaging technique with phase object. With the help of additional nanosecond laser Z-scan measurements, the parameters associated with the five-level model used to interpret the experimental results are uniquely determined. Unusually large absorption cross sections for the first singlet excited state and for the lowest triplet excited state as well as a rather short intersystem crossing time are found in this system, suggesting ZnPcBr4 (a phthalocyanine) to be an effective optical limiter. The intensity-dependent refractive index of neat dimethyl sulfoxide (DMSO) and the excited-state contribution to the nonlinear refractive index of the solution are also determined. (c) 2009 Optical Society of America