Optics with Gaussian Beams

Abstract

The general public holds the notion of a laser beam as a cylindrical bundle of rays that travels arbitrary distances without any change of its diameter so that it delivers the same power density wherever it hits. Take note, James Bond: There is no such thing as a cylindrical beam. The laws of diffraction make sure that any beam with a finite diameter widens as it propagates; the wider the beam starts out, the more gradual is its spreading, but it is always there.