High-aperture beams

Beams of a high angle of convergence and divergence are called high-apertur e beams. Different ways of defining high-aperture generalizations to paraxi al beams are reviewed for both scalar beams and electromagnetic beams. The different approaches are divided into three types. The particular examples of Gaussian beams and Bessel beams are discussed. For Gaussian beams, beams that exhibit a Gaussian variation in the waist necessarily include evanesc ent components, which rules out their use in describing propagation over al l space. Generalizations of the definitions of beam width and the beam-prop agation factor M-2 for high-aperture beams are described. The similarities among the three types of high-aperture beams and the different models of ul trashort-pulsed beams are discussed. (C) 2001 Optical Society of America.