Linear and Femtosecond Optical Nonlinear Properties of Au/Al2O3 Thin Films Prepared by a Sputtering Method

Au nanoparticles embedded in Al2O3 thin films (Au/Al2O3 films) with a high concentration of Au particles (8-28 at. %) were prepared by a multitarget sputtering method. The size of Au nanoparticles was controlled by the deposition time of Au during the sputtering. In the optical absorption spectra of the Au/Al2O3 film with the mean Au particle diameter of 4.2 nm, the absorption peak due to the localized surface plasmon resonance (LSPR) of the Au particles was observed at 557 nm. The real and imaginary parts of the third-order nonlinear susceptibility, Re[chi((3))] and lm[chi((3))] of the film measured at 540 nm by the femtosecond Z-scan technique were estimated to be 2.1 x 10(-9) and -6.5 x 10(-9) esu, respectively. The nonlinear response time derived from the recovery time of the nonlinear absorption was estimated to be 1.7 ps at the absorption peak of the LSPR. (C) 2011 The Japan Society of Applied Physics