Abstract

Au and Cu ions implanted in Corning 7940 glass and fused silica form metallic nanoclusters exhibiting a large third-order optical nonlinearity. The sign and magnitude of all components of χ⁽³⁾ were measured for linearly and circularly polarized picosecond laser pulses at wavelengths near the surface plasmon resonance, by using both Z-scan and degenerate four wave mixing techniques. The data show that clusters over ~30 Å diameter retain bulk crystalline structure with a cubic class m3m symmetry. For smaller clusters χ⁽³⁾ has isotropic symmetry. The nonlinear index of refraction is size dependent for clusters with crystalline structure; for the smaller clusters, the size dependence is not so apparent. Detailed analysis of the results shows that the main contribution to χ⁽³⁾ arises from hot electrons and interband transitions.

© 1992 Optical Society of America