Exact Partial Wave Expansion of Optical Beams with Respect to an   Arbitrary Origin
  Using an analytical expression for an integral involving Bessel and Legendre functions we succeeded to obtain the partial wave decomposition of a general optical beam at an arbitrary location from the origin. We also showed that the solid angle integration will eliminate the radial dependence of the expansion coefficients. The beam shape coefficients obtained are given by an exact expression in terms of single or double integrals. These integrals can be evaluated numerically in a short time scale. We presented the results for the case of linear polarized Gaussian beam. 
Antonio Alvaro Ranha Neves, Adriana Fontes, Lazaro Aurelio Padilha,   Eugenio Rodriguez, Carlos Henrique Brito Cruz, Luiz Ca...