Observation of interaction forces between one-dimensional spatial solitons in photorefractive crystals.

We propagate two coherent and parallel beams of a He-Ne laser through a Bi(12)TiO(20) photorefractive crystal in the presence of drift nonlinearity. Our experimental results demonstrate that the beams attract or repel each other according to their initial phase difference. They attract each other when they are initially in phase and they repel each other when they are initially out of phase.