Saturation effects in silver-particle aggregates due to nonliearity

We present results for the extinction and absorption spectra of fractal aggregates consisting of silver particles, calculated in the quasistatic dipole approximation. We have solved the coupled-dipole equations iteratively, taking into account the nonlinear susceptibility kai3(Kerr), which is introduced in terms of an intensity-dependent dielectric function. To achieve self consistency, we used a modified version of Broyden's mixing method. Nonlinearity is seen to supress the giant enchancement effects found for linear polarizability. At intermediate intensitites, we observe a tendency toward saturation and some hysteretic behaviour which is reminiscent of ferro-electrics. For fractal aggregates of particle radii in the 3-5 nm range, the behaviour is determined by saturation and nohysteretic effects are observed. \newline \newline [1] G. Amoretti et al., Phys. Rev. B 15 (1989) 1856