Internal and near-surface electromagnetic fields for a spherical particle irradiated by a focused laser beam

Theoretical expressions for the internal and external electromagnetic fields for an arbitrary electromagnetic beam incident upon a homogeneous spherical particle are derived, and numerical calculations based upon this theoretical development are presented. In particular, spatial distributions of the internal and near-surface electric field magnitude (source function) for a focused fundamental (TEM₀₀ mode) Gaussian beam of 1.06 μm wavelength and 4 μm beam waist diameter incident upon a 5-μm-diam water droplet in air are presented as a function of the location of the beam focal point relative to the sphere center. The calculations indicate that the internal and near-surface electric field magnitude distribution can be strongly dependent upon relative focal point positioning and may differ significantly from the corresponding electric field magnitude distribution expected from plane-wave irradiation.