title: Gaussian beam formulas from diffraction theory.
abstract: A simple, single-mode, coherent Gaussian laser beam with wavefronts that are spherical as they pass through a reference plane is assumed, and then by using only the Huygen's principle and scalar diffraction theory, the propagation characteristics are found, and the formulas for the beam at a distance from the reference plane are derived. The action of a lens on a wavefront is discussed, and the lens formula is derived.
authors.forename: C S
authors.initials: CS
authors.lastname: Williams