Fabry-Pérot and ring cavity configurations and transverse optical patterns

The properties of travelling- and standing-wave resonators and their influence on the modal composition and propagation of transverse patterns are analysed and a prescription for constructing a travelling-wave resonator 'equivalent' to a standing-wave resonator is given. It is shown that the presence of an intracavity nonlinear medium invalidates the equivalence between the two kinds of cavity, even when the interference between the counterpropagating waves can be neglected. Therefore great care has to be taken when comparing experimental and theoretical results obtained in different types of cavity, since in general their properties differ. Some implications concerning the appearance of phase singularities in the two kinds of resonator are discussed.