Pulse duration dependence of the third order optical nonlinearity of a cadmium sulfide dendrimer nanocomposite

Open and close aperture Z-scans were performed on various CdS quantum dots embedded in either generation 4 (G4) and G5 poly(propyleneimine) dendrimer films using picosecond and femtosecond pulses between 350 nm and 1 &mgr;m. The films had an average thickness of 400nm. The measured values of the third order nonlinear coefficient were among the highest off-resonance nonlinearities reported for organic and/or hybrid composites materials. However, the nonlinear response with picosecond pulses were about an order of magnitude higher than the femtosecond counterpart. We show that the nonlinear response in these materials is also a function of the dynamics of the excited states involved and that measurements of the nonlinear optical coefficient with pulses of different duration is directly correlated to the dynamics of the excited states.