Small-particle composites. II. Nonlinear optical properties

Five Orders-of-Magnitude Enhancement of Two-Photon Absorption for Dyes on Silver Nanoparticle Fractal Clusters

“…10 This is consistent with the fact that the nanoparticle aggregates formed in colloidal solution through the mechanism of cluster-cluster aggregation (CCA) have a fractal geometry 32 that closely approximates that of the simulated CCA aggregates for which extremely large enhancements have been calculated. 33 In contrast, the evaporated films have a far more regular "droplet-like" structure. 34 The large enhancement of two-photon absorption by metal nanoparticle fractal clusters has potential for application in ultrasensitive detection of molecular binding, 35 imaging, and localized activation of photochemical processes.…”

Electromagnetic field fluctuations and optical nonlinearities in metal-dielectric composites

“…(2.21) and (2.22), do not require long-range spatial correlations (such, for example, as in fractal structures) in particle positions. The large "eld #uctuations have been seen in computer simulations, in particular, for the so-called random gas of metal particle [26,24], i.e., for metal particles randomly distributed in space. This, however, is not true when the contrast is large " "< ; we show below that in this case the internal structure of a composite becomes crucial.…”

“…Since distribution of the local "eld does not change when bond conductances are multiplied by the same factor it is convenient to consider the lattice where a bond conductance takes value "!1#i with probability p (¸bonds) and "1 with probability 1!p (C bonds). Since the absolute values of and are very close, the standard method, using the percolation theory scaling approach [12,20,24,64] and based on the assumption of large di!erence between the two components conductivities, cannot be used, even to estimate the spatial distribution of the "eld in the system. This is the reason why computer simulation has been used in the works [36,37,44].…”

Direct observation of localized dipolar excitations on rough nanostructured surfaces

“…[6][7][8] Resonant dipolar excitations in fractal structures also can be localized in subwavelengthsized regions but, being the result of multiple scattering, exhibit strong frequency and polarization dependence of their spatial location. 9,10 This also means that the spatial location of light-induced dipole excitations is determined not only by the local topography, but also by the large-scale geometrical structure. Note that these features of light localization in fractals are similar to those observed for localization of surface plasmon polaritons ͑SPP's͒, 11,12 which is also an interference phenomenon related to multiple scattering of SPP's ͑in the surface plane͒ caused by the surface roughness.…”