Analytic expressions for the time-averaged electromagnetic energy within a dispersive and absorbing sphere on which a plane wave is incident are derived. Numerical results are presented for diatomic ionic crystal spheres and for metallic, nearly free-electron-like spheres. It is found that the stored energy exhibits resonant enhancement near resonances of the sphere’s extinction cross section. In the Rayleigh region the energy increase at resonance may amount to more than three orders of magnitude. The energy formula is applied to the calculation of the energy transport velocity in a disordered medium containing dispersive spheres.
© 1998 Optical Society of America
R. Ruppin, "Electromagnetic energy in dispersive spheres," J. Opt. Soc. Am. A 15, 524-527 (1998)