Optical nonlinearities of a high concentration of small metal particles dispersed in glass: copper and silver particles

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Abstract
Third-order nonlinearities of glasses doped with a large number of copper or silver particles are studied by degenerate four-wave mixing with an emphasis on particle-size dependence. The nonlinear susceptibility χ(3) exhibits a peak at the wavelength of the absorption peak, with a maximum value of the order of 10−7 esu. The value of χ(3)/α is roughly independent of the absorption coefficient α and increases as the particle radius increases. This result is well explained by the size dependence of the imaginary part of the dielectric constant of metal particles and the local-field factor. The time response of the nonlinearity exhibits two-component behavior: the fast decay time is shorter than the pulse width of the laser (~12 ps), whereas the slow one is 120–200 ps, being weakly dependent on the radius.