Optical nonlinearity of Au nanoparticles fabricated by negative ion implantation

Dispersion of the nonlinear dielectric function of Au nanoparticle composites in Al2O3, fabricated by negative ion implantation, was studied. Negative ion, Au−, with 60 keV was applied for implantation at a flux of 10 μA/cm2, achieving a fluence up to 2 × 1017 ions/cm2 to fabricate the Au nanoparticles. The surface plasmon resonance of Au:Al2O3 composite showed a blue shift due to a shallow distribution of Au nanoparticles in Al2O3. Transient transmission and reflection spectra were measured with the pump–probe method using a femtosecond laser system. The dispersion of the nonlinear dielectric function of Au:Al2O3 composite is evaluated from these transient spectra with total differential. The evaluated dispersion around the surface plasmon resonance was compared with calculated dispersions including interband and intraband transitions and a local electric field factor. The dispersion reflects the overlap with these transitions.