ABSTRACT
This chapter presents an alternative treatment based purely on geometrical optics. Because of the deep underlying similarity between geometrical optics and classical mechanics, it outlines the same formalism may be applied to the analysis of laser beams. A method is presented for the description of laser beams in phase space in combination with exact ray tracing algorithms. With this method, it is possible to trace single mode and multimode Gaussian beams, as well as beams from unstable resonators. A parallel light beam only exists in theory and an exact ray tracing analysis of an optical system is as good or as bad as the description of the ray ensemble of the actual light source. The reliability of the results from beam tracing depends on the accuracy of the definition of the input ray ensemble. When one has to design optics for a specific laser it is necessary to determine the characteristics of the beam.
