Depolarization of Light at the Frequency of Localized Surface Plasmon Resonance as the Probe of Interparticle Interaction

Spectroscopic ellipsometry with the account of depolarization applied for few disordered layers of nanoparticles demonstrated different level of depolarization at the frequency of the localized plasmon depending on the temperature of annealing. The temperature of annealing higher the level of depolarization lower. Scanning electron microscopy revealed the shape and size distribution of nanoparticles, which approaches the layer of practically round nanoparticles produced at highest annealing temperature and rather shapeless particles for lowest annealing temperature.

We speculate that for the creation of depolarized light scattered by the layer of nanoparticles the energy of localized plasmon should be stored and the excitation should be dephased in some noninstant process. We propose the model of the Forster energy transfer between plasmons localized at different nanoparticles as such a process. This process can easily create dephasing at the energy migration and storing. Additionally such a transfer should be greatly enhanced at the frequency of the resonance as it is proportional to the multiplication of dipole moments of participating particles what we observe in the experiment.

At the same time, only dephasing is not enough for the creation of depolarization as even completely incoherent light may be totally polarized. It is the particle shape, which can give us the necessary disorientation of dephased dipoles. If all particles are round the direction of the excitation at the resonance frequency is degenerated. In such a case the transferred excitation would have the same orientation of the dipole moment as the initial one, so all scattered light will keep the polarization. The opposite situation is for shapeless particles. In this case the dipole moment of the resonance of the acceptor may be disoriented according to the dipole moment of the resonance of the donor, what gives the second necessary element for the creation of depolarization.

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