Energy flow around a small particle investigated by classical Mie theory

Abstract

The field lines of Poynting vector around a small particle are investigated on the basis of classical Mie theory. A particle can effectively absorb incident energy near the optical resonance, where its optical absorption cross-section becomes much greater than its geometrical cross-section. It is shown that absorbed energy flows into the particle through some limited portion of its surface (``input window'') instead of the whole surface as it follows from the dipole approximation. This ``input window'' expands with the increasing value of the imaginary part ${\ensuremath{\epsilon}}^{\ensuremath{''}}$ of the dielectric function of the particle. For a small ${\ensuremath{\epsilon}}^{\ensuremath{''}}$ the absorbed energy is released by the plasmon radiation. Interference of this radiation with the incident wave creates complex patterns of energy flux in the near-field region. These patterns cannot be understood within the frame of a dipole approximation and the terms of higher orders with respect to size parameter $q=2\ensuremath{\pi}a∕\ensuremath{\lambda}$ ($a$ is the radius of the particle and $\mathit{\ensuremath{\lambda}}$ is radiation wavelength) should be taken into account.