Failure of the optical theorem for Gaussian-beam scattering by a spherical particle

摘要: It is shown that when an electromagnetic wave with some degree of amplitude rolloff in the transverse direction scattered by a spherical particle, optical theorem not valid. For such shaped beams extinction cross section may be written as infinite series powers reciprocal beam width. The imaginary part forward-scattering to first term this series. Two approximations are presented for special case Gaussian-beam scattering. one based on dominance diffraction forward w0 ≳ a, where half-width and target particle radius. second approximation, valid ≲ transmission-compensating field interference.