INTERNAL ELECTRIC ENERGY IN A SPHERICAL-PARTICLE ILLUMINATED WITH A PLANE-WAVE OR OFF-AXIS GAUSSIAN-BEAM

The electric energy in a lossless or lossy spherical particle that is illuminated with a plane wave or a Gaussian beam is investigated. The analysis uses a combination of the plane-wave spectrum technique and t he T-matrix method. Expressions for the electric energy in any mode al l well as the total electric energy inside the particle are given. The amount of energy coupling into the particle for different beam illumi nations is also investigated. The high-Q (low-order) resonant modes ca n dominate the electric energy inside a spherical particle many linewi dths away from the resonance location, particularly if the beam is foc used at the droplet edge or outside the droplet. If the sphere is loss y, low-order modes can still dominate the electric energy if the beam is focused far enough outside the sphere. As the absorption coefficien t of the particle increases, the energy in a high-Q mode decreases muc h faster at the resonance frequency than it does at near or off-resona nce frequencies. The effects of the absorption on the dominance of the internal fields by a high-Q mode decreases as the beam is shifted far ther away from the particle. As the beam is shifted farther away from the particle the fraction of the incident energy coupled into the sphe re at resonance first increases and then decreases. Although the coupl ed energy decreases as the beam is shifted farther from the sphere, mo st of that energy is in the lowest-order mode.