Enhancement of third-order nonlinear optical susceptibilities in silica-capped Au nanoparticle films with very high concentrations

Third-order nonlinear optical susceptibilities (χ(3)) and response times have been investigated for silica-capped Au nanoparticles for various volume fractions, p, of Au nanoparticles ranging from 0.027 to 0.66. The imaginary part of χ(3)(Im χ(3)) around the surface plasmon resonance increases with increasing p up to 0.34, and decreases for p>0.39. In addition to the local field enhancement around the surface plasmon resonance in the composite system, an additional enhancement of Im χ(3) due to the interaction between nanoparticles for p<0.39 is observed.