Systems of small metal particles: Optical properties and their structure dependences

Experiments on small particles usually require samples containing large numbers of particles. The properties of such samples are determined both by the properties of the individual particle and by collective effects, if particles are packed closely together. Collective optical effects strongly depend on the topography of the samples. It is shown that they can be classified according to the effective local electromagnetic field. Recent experiments and calculations are presented for optical extinction spectra in the spectral region of plasmon polariton excitations, which clearly show the different behaviour of effective medium-like samples and of samples containing particle aggregates.