The story has it that, when Schwinger learned of the Feynman diagrams, he remarked that quantum electrodynamics had been brought to the masses. A similar statement could be applied to photorefractive (PR) solitons. In fact, among the family of known optical self-trapped waves, PR solitons are of an altogether peculiar nature: they are the consequence of an extended buildup in time of optical nonlinearity. As a consequence, although the generation of a spatial soliton in conventional nonlinear media requires the use of high optical powers and sophisticated experimental techniques, its observation in PR media requires a few milliwatts of continuous-wave laser power and accessible experimental apparatus. In other words, the discovery that PR crystals support spatial nonlinear waves has profoundly altered the rules of the game and has rapidly shifted attention from soliton generation physics to the rich realm of soliton phenomenology. This circumstance has produced the involvement of a relatively large number of experimental groups, making the topic a field in its own right.
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