ABSTRACT
This entry presents the paraxial approach and its most relevant uses. A combination of optical systems may be described by the paraxial approach. Some implications of the paraxial approach in the framework of the physical optics are analyzed. Equations describing the propagation of an electromagnetic wave are expanded and analyzed; they demonstrate that Fraunhofer diffraction lies within the paraxial regime. Finally, a discussion is presented on the relation of the paraxial approach with geometrical optics.
