TEMPORAL BEHAVIOR OF BIDIMENSIONAL PHOTOREFRACTIVE BRIGHT SPATIAL SOLITONS

The time behavior of bright spatial solitons in biased photorefractive media is investigated within the framework of a bidimensional band tr ansport model. Biasing the photorefractive media requires an externall y applied electric field or the presence of a photovoltaic effect. The se two basically different phenomena are shown to be equivalent and ad ditive. The mechanism of space-charge field buildup is analytically ex pressed, leading to a time-dependent wave propagation equation in gene ric photorefractive media. The temporal behavior of the soliton soluti ons to this equation is investigated. It shows the evolution of the so liton beam from the time the external electric field is applied to the final steady-state soliton. On the way, the so-called quasisteady sol iton is retrieved, along with its properties. Furthermore, the photovo ltaic soliton is described by the wave propagation equation: its behav ior is the same as that of the steady-state soliton, the transient sta tes included. Finally, low-power photorefractive bright spatial solito ns are generated in a Bi12TiO20 crystal with a He-Ne laser and their t emporal behavior is investigated, thus providing an experimental valid ation of our theoretical considerations.