Spectral dependence of selective photomodification and localization of optical excitation in silver fractal clusters

Summary form only given. Irradiation of a nanocomposite medium, consisting of metal fractal clusters, by a strong laser pulse leads to the photoburning of a dichroic hole in the absorption spectrum near the laser wavelength. This phenomenon was interpreted as resulting from the localization of excitations in fractal clusters. It was shown theoretically that the dipole (polar) eigenmodes formed by the interaction of monomers in cluster are localized in domains that are smaller than both the optical wavelength and the cluster size. The threshold photoburning of resonance eigenmodes responsible for light absorption results in the appearance of a hole in the absorption spectrum. In the present paper, we demonstrate experimentally for the first time that photomodification of Ag fractal clusters occurs. The number of resonance monomers varies inversely to the detuning of the exciting laser from the plasmon resonance.