Large local optical activity in fractal aggregates of nanoparticles

Large local optical activity in fractal aggregates of silver nanoparticles has been observed by means of photon scanning tunneling microscopy. The effect occurs because resonant plasmon modes in random fractals can have handedness in spatial distribution of their amplitudes. In agreement with experimental observations, numerical simulations show dramatic difference in dipole-moment distributions for right- and left-circularly polarized incident light when the cluster size is comparable with or larger than the wavelength. Variations in the local parameter describing the circular intensity difference of scattered light show that fractal aggregates are characterized by broad and random distributions of chiral plasmon modes.

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