Photorefractive Spatial Solitons
Light solitons in space (spatial solitons) exhibit a dual behavior of both waves and particles. They form when light interacts with the medium of propagation in a manner that exactly compensates for diffraction. This results in self-trapping of the light beam. It is obvious, however, that, since the medium is required to modify its properties in the presence of light, a strong light-matter interaction is required, i.e., the material must possess optical nonlinearities. All optical solitons that have thus far been discovered are a consequence of material non-linearities that are proportional to the absolute light intensity (Kerr-like solitons). Therefore, they typically require intensities of the order of kW-MW/ cm2 for their operation threshold. On the other hand, photorefractive (PR) materials, which have been studied over the last two decades, possess strong nonlocal nonlinearities that do not depend upon the absolute light intensity. It was not initially obvious, however, that these materials are also capable of forming optical solitons.
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