Ultrafast nonlinear optical response of silver/bismuth oxide nanocomposite films with different silver concentrations

The ultrafast nonlinear optical properties of co-sputtered silver/bismuth oxide (Ag:Bi₂O₃) nanocomposite films with different Ag concentration (13.2-59.3 at%) were investigated by femtosecond (fs) pump-probe and fs optical Kerr effect (OKE) techniques. The pump-probe measurements revealed the Ag concentration-related energy relaxation dynamics: for films with high concentration of Ag (> 50%), the relaxation dynamics consist of a fast excitation power-dependent component (1-2 ps) and a long-lived component (< 100 ps). While for films with relative low Ag concentration (<40%), the energy relaxation behaves as a single exponential process, nearly completed within 1 ps. This Ag concentration related dynamical behavior was suggested to be originated from the differences in the structural and thermal properties of both Ag nanoparticles and Bi₂O₃ matrices. The result of the femtosecond OKE measurements showed that the third-order susceptibilities (χ(3)) of Ag:Bi₂O₃ films have a maximum of 4.1×10^-10 esu at Ag concentration of 35.7%.