Metal nanoparticles–silica composites: Z-scan determination of non-linear refractive index

Metal quantum-dot composite glasses can exhibit an enhanced optical Kerr susceptibility, χ(3), whose real part is related to the n2I coefficient of the intensity-dependent refractive index. We used the Z-scan technique for measuring the n2I’s of micrometric composites films formed by copper with nanometer sized particles embedded in silica glass by means of radiofrequency magnetron sputtering technique, followed by thermal annealing in reducing atmosphere, to promote cluster growth. A single 6 ps long pulse at a repetition rate of 1 Hz was used to determine the picosecond fast (noncumulative, electronic) response of the composites. We obtain n2I from (0.48±0.24)×10−11 to (2.0±1.0)×10−11 cm2/W and β of (3.1±1.6)×10−7 to (8.5±4.2)×10−7 cm/W in the explored range of Cu/SiO2 composition.