Fractals in microcavities: Giant coupled, multiplicative enhancement of optical responses

A novel class of optical materials, microcavities doped with nanostructured fractal aggregates, was studied. Fractal aggregate optical excitations may be concentrated in regions smaller than the diffraction limit of conventio nal optics, resulting in large local fields. Seeding the aggregates into mi crocavities further increases the local fields because of light trapping by microcavity resonance modes. These microcomposites possess unique optical properties, including very large probabilities of radiative processes. In o ur experiments, lasing at extremely low pump intensities, below 1 mW, and s trongly enhanced Raman scattering was observed in fractal-microcavity-dye c omposites.