Vectorial analytical description of propagation of a highly nonparaxial beam

We present a formalism describing optical propagation in a homogeneous medium of a fully vectorial highly nonparaxial field, characterized by a waist smaller than the wavelength. The method allows us to derive an analytical expression for a field possessing an initial Gaussian transverse distribution of width w, in the extreme nonparaxial regime w < lambda, valid for propagation distances z greater than or similar to d, where d = w(2)/lambda is the diffraction length. (C) 2002 Elsevier Science B.V. All rights reserved.