Nonlinear optical properties of Cu nanoparticles in various insulators fabricated by negative ion implantation

Linear and nonlinear optical properties were studied for Cu nanoparticle composites with numerical calculation of the local electric field inside a nanoparticle. Negative Cu ions of 60 keV were implanted into amorphous SiO2 and single crystals of SrTiO3 and TiO2 at a fixed dose rate of 10 μA/cm2 to a total dose of 1×1017 ions/cm2. The surface plasmon peak shifted to red and was enhanced with increasing refractive index values of the substrate. Complex nonlinear optical constants were evaluated by the z-scan method with a tunable femtosecond laser system over a range from 2.0 to 2.3 eV. The complex third-order optical susceptibility of the Cu:SiO2 nanoparticle composite exhibited values of +1.6 to −3.1×10−9 esu around the surface plasmon resonance and took a maximum at 2.1 eV. The real part indicated negative values over the range and the imaginary part changed from positive to negative toward the higher photon energy. Both parts steeply vary with the photon energy near the surface plasmon resonance. The dispersion roughly reflects the local field factor.