The paraxial wave equation describes many problems in Physics and Engineering. For instance, the Schrödinger equation describing non-relativistic particles can be considered as a paraxial approximation of the relativistic quantum mechanics. The paraxial equation also emerges in the study of the electromagnetic waves propagation in a large number of physical situations. In this contribution we present an overview of the paraxial wave equation and its derivation in relevant problems for Physics and Engineering. Analogies between the electromagnetic paraxial equation and the quantum mechanical Schrödinger equation are discussed, as well as the relationship between paraxiality and transversality of electromagnetic waves. Finally, a few interesting examples of wave propagation in the paraxial limit are considered.
electromagnetic waves; paraxial equation; Schrödinger equation
