Parallel propagation of coherent bright beams in a self-defocusing photorefractive crystal

Summary form only given. Photorefractive crystals are very versatile media for experiments on spatial soliton because they need very low intensities (/spl mu/W/cm/sup 2/) and the sign of the nonlinearity can be switched from positive to negative changing the polarity of the external electric field applied to the crystal. With the parallel propagation of bright beams with a separation shorter than the width it is possible to generate output intensity distributions similar to dark spatial solitons when the relative phase between the beams is /spl Pi/.