Anisotropic nonlinear optical absorption of gold nanorods in a silica matrix

Nanocomposite films consisting of gold nanospheres or gold nanorods embedded in a silica matrix have been prepared using a hybrid deposition technique consisting of plasma-enhanced chemical vapor deposition Of SiO2 and co-sputtering of gold, followed by annealing at 900 degrees C. Subsequent irradiation with 30 MeV heavy ions (CU5+) was used to form gold nanorods. Linear and nonlinear optical properties of this material are closely related with the surface plasmon resonance in the visible. The nonlinear absorption coefficient (alpha(2)@532 nm) for the films containing gold nanospheres was measured by Z-scan and P-scan techniques, and it was found to be isotropic and equal to -4.8 x 10(-2) cm/W. On the contrary, gold nanorods films exhibited two distinct surface plasmon resonance absorption bands giving rise to a strong anisotropic behavior, namely a polarization-dependent linear absorption and saturable absorption. Z-scan and P-scan measurements using various light polarization directions yielded nonlinear absorption coefficient (alpha(2)@532 nm) values varying from -0.9 x 10(-2) cm/W up to -3.0 x 10(-2) cm/W. Linearity of the P-scan method in the context of nanocomposite saturable absorption is also discussed. (c) 2007 Elsevier B.V. All rights reserved.