title: Origin of third-order optical nonlinearity in Au:SiO(2) composite films on femtosecond and picosecond time scales.
abstract: Three sorts of probe laser, which have pulse durations of 200 fs, 35 ps, and 70 ps, were employed in the measurement of the third-order nonlinear optical susceptibility x((3)) in Au:SiO(2) composite films in a degenerate four-wave mixing scheme. We found that the composite films at their absorption peak (~550 nm) had a maximum x((3)) , which depends strongly on the pulse width of the probe laser. The value of x((3)) measured with a 70-ps laser was ~30 times larger than that measured with a 200-fs laser. The time-resolved measurements revealed that the optical nonlinearity on the femtosecond time scale is attributable mainly to contributions from the interband electric-dipole transition (especially at low concentrations) and partly to those from hot electrons rather than being dominated by hot-electron excitation in the picosecond regime.
authors: H B
authors: HB
authors: Liao
authors: R F
authors: RF
authors: Xiao
authors: J S
authors: JS
authors: Fu
authors: H
authors: H
authors: Wang
authors: K S
authors: KS
authors: Wong
authors: G K
authors: GK
authors: Wong