Energy flow around a small particle investigated by classical Mie theory

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 ${\epsilon }^{″}$ of the dielectric function of the particle. For a small ${\epsilon }^{″}$ 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 $q=2\pi a∕\lambda$ ($a$ is the radius of the particle and $\mathit{\lambda }$ is radiation wavelength) should be taken into account.