Femtosecond nonlinear optical properities of PbS nanoparticles

We report on the ultrafast carrier dynamics and the nonlinear optical properties of PbS nanoparticles at various energy fluences. At low pump fluences both photo-induced absorption of biexciton and photobleaching of the exciton were observed at the same time. On the contrary, the induced absorption dominates the temporal behavior in the femtosecond domain, indicating that biexciton effect was strongly dependent on the density of excited carriers and started to play a significant role at the multiple e-h pair excitation per nanoparticle. The magnitude of χ (3) for PbS nanoparticles doped SiO2 thin film was calculated to be 5.1x10-10 esu, which came from the contribution of biexciton effect at high pump intensity