Phase Domains and Phase Solitons

Abstract

The radiation emitted by lasers and other laser-like nonlinear optical systems, such as nondegenerate optical parametric oscillators and photorefractive oscillators, has a free phase: above the generation threshold the field intensity is fixed, but the phase can take an arbitrary value. The generation threshold in laser-like systems is usually characterized by a supercritical Hopf bifurcation (Fig. 8.1a). As a consequence, the corresponding order parameter equation is the complex Ginzburg—Landau or the complex Swift—Hohenberg equation (or a generalization of one of those equations) as discussed in Chaps. 2 and 3. In Chaps. 8–10 we have seen that for some kinds of systems (e.g. in the presence of an intracavity saturable absorber or with an intracavity focusing/defocusing material), the bifurcation from the nonlasing to the lasing state can also be subcritical (Fig. 8.1b). Owing to this subcriticality, or equivalently owing to the amplitude bistability, switching waves between bistable states, amplitude domains, and spatial solitons in the form of amplitude domains of minimum size are possible.