Spatial and temporal phase coexistence in optical bistability

Optical bistability is a first-order nonequilibrium phase transition, which is characterized by the spatial or temporal coexistence of two phases. In systems with resonators this phase coexistence can be realized in the form of transverse patterns of high and low intensity values, whereas in a resonatorless optical bistability the phase coexistence becomes manifest in a longitudinal intensity variation. In systems in which strong diffusion of the elementary excitations suppresses spatial phase coexistence, random fluctuations establish at least in principal a temporal phase coexistence by stochastic switching between the two bistable states.