Third-order optical nonlinearity of a transparent glass ceramic containing sodium niobate nanocrystals

Measurements of the third-order nonlinear refractive index, ${n}_{2},$ and the two-photon absorption coefficient, ${\ensuremath{\alpha}}_{2},$ of a transparent niobic silicate nanocomposite are reported. Samples with various filling factors, $f,$ of sodium niobate nanocrystals were studied at 1064 nm, 800 nm, and 532 nm. $Z$-scan and Kerr gate techniques were applied using picosecond and femtosecond lasers. The response time of the nonlinearity was demonstrated to be smaller than 100 fs. An explanation is given for the observed spectral behavior of ${n}_{2}$ and ${\ensuremath{\alpha}}_{2},$ and a quantitative approach of their dependence with $f$ is presented in terms of a generalized Maxwell-Garnet model. Possible uses of the nanocomposite for all-optical switching applications are evaluated.