Focused electromagnetic beams are frequently modeled by either an angular spectrum of plane waves or a partial-wave sum of spherical multipole waves. The connection between these two beam models is explored here. The partial-wave expansion of an angular spectrum containing evanescent components is found to possess only odd partial waves. On the other hand, the partial-wave expansion of an alternate angular spectrum constructed so as to be free of evanescent components contains all partial waves but describes a propagating beam with a small amount of standing-wave component mixed in. A procedure is described for minimizing the standing-wave component so as to more accurately model a purely forward propagating experimental beam.
© 2006 Optical Society of America
Original Manuscript: March 16, 2006
Revised Manuscript: May 22, 2006
Manuscript Accepted: May 23, 2006
James A. Lock, "Partial-wave expansions of angular spectra of plane waves," J. Opt. Soc. Am. A 23, 2803-2809 (2006)