Contribution of the two-photon absorption to the third order nonlinearity of au nanoparticles embedded in TiO₂ films and in ethanol suspension

We measured the absorptive and refractive nonlinearities in Au nanoparticles when they are embedded in a TiO₂ film and when they are suspended in ethanol. The morphology of the nanoparticles was estimated by using HRTEM microscopy. Different contributions related to electronic polarization and two-photon absorption were observed in the samples using a self-diffraction technique with pulses of 26 ps at 532 nm. Transmittance experiments were performed in order to confirm the mechanisms of optical absorption. The Au nanoparticles were grown by the photoreduction of TiO ₂ sol-gel solutions which contain Au³⁺ ions. The thin films were prepared by using the dip coating technique with fresh UV exposed sol-gel solutions. We observed that when the sample does not present any important nonlinear absorption it is possible to enhance the participation of the nanoparticles in the optical Kerr response of the media.