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.