Lasing at extremely low pump intensities, below 1 mW, and dramatically enhanced Raman scattering were observed for a novel class of optical materials, microcavities doped with nano-structured fractal aggregates. Nano-structured fractal aggregates lead to giant local-fields concentrated in "hot spots" much smaller in size than the size of the fractal and the wavelength. Coupling the localized plasmon modes in fractal aggregates with microcavity resonances further increases the local fields. These microcomposites possess unique optical characteristics, including extremely large probabilities of radiative processes. An extremely pronounced time-dependent lasing effect of dye molecules adsorbed on silver particles was also observed in oar experiment This time dependence is likely due to photo-stimulated aggregation of silver colloid particles and the gradient forces pulled fractal aggregates into the high-field area associated with the morphology-dependent resonance mode.
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