Three-wave simultons: Quasi-particles in quadratic media

Self-guided multi-frequency waves or simultons can form and propagate in media exhibiting a quadratic nonlinear susceptibility and, specifically, able to generate second harmonic. Some of their relevant properties are discussed, illustrating beam cleanup, instability, switching, steering, collisional interactions and other features in the spatial and temporal domains, including energy localization and gap solitons in periodic structures