PLANE-WAVE SPECTRUM OF ELECTROMAGNETIC BEAMS

A plane wave spectrum method of Gaussian beams can be derived by using Davis' approximations for the vector potential. An equivalent vector potential is introduced by considering the inverse Fourier transform o f the spectrum function of the original vector potential in a given pl ane. The electromagnetic field, which corresponds to the equivalent ve ctor potential, satisfies Maxwell's equations and can be written as a sum of plane waves. The beam shape coefficients, or the expansion coef ficients in terms of regular spherical vector wave functions, are expr essed as simple integrals. This version of the plane wave spectrum met hod offers the possibility to compute higher-order corrections for Gau ssian beams.