Femto-, pico- and nano-second refractive nonlinearities exhibited by Au nanoparticles

Gold nanoparticles (AuNPs) have proven to be powerful tools in various ultrafast photonic, plasmonic and nanomedical applications. Numerous advances in the use of AuNPs include research on their interesting and remarkably fast changes influenced by Surface Plasmon Resonance excitations. Within this work we report theoretical and experimental results for the physical mechanisms that originate a nonlinearity of refractive index during different temporal regimes for a high-purity silica matrix containing Au nanoparticles. The nanocomposites were prepared by ion implantation into a silica matrix, followed by a thermal annealing. We used an optical Kerr gate with 80 fs pulses at 830 nm and a vectorial self-diffraction technique with 26 ps and with 7 ns at 532 nm in order to investigate the magnitude and response time of the resulting third order nonlinearity. In all cases we were able to measure and identify an electronic polarization responsible for the nonlinear refraction. For the pico- and nano-second near resonance irradiations, a contribution of a thermal effect could be stimulated and then the optical Kerr response enhanced. The presence of saturable absorption for the pico- and nano-second experiments was measured. We observe that our samples behave like waveguides in the near infrared spectrum and we estimate that they posses potential applications for all-optical switching devices.