Off-resonant third-order optical nonlinearities of Au : SiO2 nanocomposite films

Abstract

Metal nanocomposites containing An nanoparticles embedded in SiO2 were deposited on fused silica substrates by alternating sputtering of SiO2 and An at a substrate temperature of 300 degrees C and a constant volume fraction of 1 %. The nanocomposite films were prepared with different An mean diameters between 2.3 nm and 5.7 nm while the overall thickness was kept constant at 600 nm. The linear absorption peaks induced by surface plasmon resonance were shifted toward longer wavelengths from 500 nm to 560 nm with increasing Au particle sizes. To estimate third-order optical nonlinearities of the Au:SiO2 nanocomposite films, such as nonlinear refraction and nonlinear absorption at off-resonant wavelengths, we applied the z-scan technique by using laser pulses from a Kerr lens mode-locked femtosecond Ti:sapphire laser at 780 nm and 820 nm and its second harmonics at 410 nm. The sign and the magnitude of experimentally obtained off-resonant third-order susceptibilities were compared with the theoretical results