Nanocrystal size dependence of the third-order nonlinear optical response of Cu:Al2O3 thin films

Metal nanocomposite thin films formed by Cu nanocrystals embedded in an amorphous ${\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ host have been synthesized by pulsed laser deposition. The mean nanocrystal diameter d was varied in the range 3.0±0.6 to 6±1 nm. The linear and nonlinear optical properties of the films were studied in the vicinity of the surface plasmon resonance and the size dependence of the third-order nonlinear optical susceptibility of the metal nanocrystals has been determined. The observed dependence ${\text{(1/d}}^3)$ indicates that in the studied diameter interval, the nonlinear response is due to quantum confinement effects in which the major contribution is associated with electronic intraband transitions.