Femtosecond Third-Order Optical Nonlinearity of Au:Bi₂O₃ Nanocomposite Films

Ultrafast third-order optical nonlinearities of the as-deposited and annealed Au:Bi₂O₃ nanocomposite films deposited by magnetron cosputtering are investigated by using femtosecond time-resolved optical Kerr effect (OKE) and pump--probe techniques. The third-order optical nonlinear susceptibility is estimated to be 2.6×10^-10 esu and 1.8×10^-9 esu at wavelength of 800nm, for the as-deposited and the annealed film, respectively. The OKE signal of the as-deposited film is nearly temporally symmetrical with a peak centred at zero delay time, which indicates the dominant contribution from intraband transition of conduction electrons. For the annealed film, the existence of a decay process in OKE signal implies the important contribution of hot electrons. These characteristics are in agreement with the hot electron dynamics observed in pump--probe measurement.