Abstract

Light beams whose transverse intensity profile is given by the zero-order Bessel function of the first kind, J₀(r), exhibit the striking feature that although their intensity is sharply peaked on the optic axis, the transverse profile is propagation-invariant. The beam exhibits no spreading over distances orders of magnitude longer than the Rayleigh range, which led to the term 'diffraction-free beam'.^1,2 It can be produced in several ways, for instance by illuminating a conical lens (axicon) with an expanded laser beam. Immediately behind the axicon, where the plane waves of the cone mutually intersect, an interference pattern appears, which is a Bessel beam. The central lobe of the Bessel function lies on the optic axis, with a typical diameter (radius at which the first zero of J₀ (r) appears) of a few microns, depending on the cone angle. When optical nonlinearities come into play, the sharp intensity peak on the optic axis gives rise to novel effects owing to the 'diffraction-free' character of the beam.³

© 1994 IEEE